Citrix Xen Xen

Xen Hypervisor VGA Memory Access Deadlock Vulnerability

CVE-2024-45818 - December 19, 2024

The hypervisor contains code to accelerate VGA memory accesses for HVM guests, when the (virtual) VGA is in "standard" mode. Locking involved there has an unusual discipline, leaving a lock acquired past the return from the function that acquired it. This behavior results in a problem when emulating an instruction with two memory accesses, both of which touch VGA memory (plus some further constraints which aren't relevant here). When emulating the 2nd access, the lock that is already being held would be attempted to be re-acquired, resulting in a deadlock. This deadlock was already found when the code was first introduced, but was analysed incorrectly and the fix was incomplete. Analysis in light of the new finding cannot find a way to make the existing locking discipline work. In staging, this logic has all been removed because it was discovered to be accidentally disabled since Xen 4.7. Therefore, we are fixing the locking problem by backporting the removal of most of the feature. Note that even with the feature disabled, the lock would still be acquired for any accesses to the VGA MMIO region.

Xen Hypervisor ACPI Table Construction Information Disclosure Vulnerability

CVE-2024-45819 - December 19, 2024

PVH guests have their ACPI tables constructed by the toolstack. The construction involves building the tables in local memory, which are then copied into guest memory. While actually used parts of the local memory are filled in correctly, excess space that is being allocated is left with its prior contents.

Arm provides multiple helpers to clean & invalidate the cache for a given region

CVE-2023-34321 3.3 - Low - January 05, 2024

Arm provides multiple helpers to clean & invalidate the cache for a given region. This is, for instance, used when allocating guest memory to ensure any writes (such as the ones during scrubbing) have reached memory before handing over the page to a guest. Unfortunately, the arithmetics in the helpers can overflow and would then result to skip the cache cleaning/invalidation. Therefore there is no guarantee when all the writes will reach the memory.

Buffer Overflow

For migration as well as to work around kernels unaware of L1TF (see XSA-273), PV guests may be run in shadow paging mode

CVE-2023-34322 7.8 - High - January 05, 2024

For migration as well as to work around kernels unaware of L1TF (see XSA-273), PV guests may be run in shadow paging mode. Since Xen itself needs to be mapped when PV guests run, Xen and shadowed PV guests run directly the respective shadow page tables. For 64-bit PV guests this means running on the shadow of the guest root page table. In the course of dealing with shortage of memory in the shadow pool associated with a domain, shadows of page tables may be torn down. This tearing down may include the shadow root page table that the CPU in question is presently running on. While a precaution exists to supposedly prevent the tearing down of the underlying live page table, the time window covered by that precaution isn't large enough.

Improper Check for Dropped Privileges

When a transaction is committed, C Xenstored will first check the quota is correct before attempting to commit any nodes

CVE-2023-34323 5.5 - Medium - January 05, 2024

When a transaction is committed, C Xenstored will first check the quota is correct before attempting to commit any nodes. It would be possible that accounting is temporarily negative if a node has been removed outside of the transaction. Unfortunately, some versions of C Xenstored are assuming that the quota cannot be negative and are using assert() to confirm it. This will lead to C Xenstored crash when tools are built without -DNDEBUG (this is the default).

NULL Pointer Dereference

Closing of an event channel in the Linux kernel can result in a deadlock

CVE-2023-34324 4.9 - Medium - January 05, 2024

Closing of an event channel in the Linux kernel can result in a deadlock. This happens when the close is being performed in parallel to an unrelated Xen console action and the handling of a Xen console interrupt in an unprivileged guest. The closing of an event channel is e.g. triggered by removal of a paravirtual device on the other side. As this action will cause console messages to be issued on the other side quite often, the chance of triggering the deadlock is not neglectable. Note that 32-bit Arm-guests are not affected, as the 32-bit Linux kernel on Arm doesn't use queued-RW-locks, which are required to trigger the issue (on Arm32 a waiting writer doesn't block further readers to get the lock).

Resource Exhaustion

The fixes for XSA-422 (Branch Type Confusion) and XSA-434 (Speculative Return Stack Overflow) are not IRQ-safe

CVE-2023-46836 4.7 - Medium - January 05, 2024

The fixes for XSA-422 (Branch Type Confusion) and XSA-434 (Speculative Return Stack Overflow) are not IRQ-safe. It was believed that the mitigations always operated in contexts with IRQs disabled. However, the original XSA-254 fix for Meltdown (XPTI) deliberately left interrupts enabled on two entry paths; one unconditionally, and one conditionally on whether XPTI was active. As BTC/SRSO and Meltdown affect different CPU vendors, the mitigations are not active together by default. Therefore, there is a race condition whereby a malicious PV guest can bypass BTC/SRSO protections and launch a BTC/SRSO attack against Xen.

Arm provides multiple helpers to clean & invalidate the cache for a given region

CVE-2023-46837 3.3 - Low - January 05, 2024

Arm provides multiple helpers to clean & invalidate the cache for a given region. This is, for instance, used when allocating guest memory to ensure any writes (such as the ones during scrubbing) have reached memory before handing over the page to a guest. Unfortunately, the arithmetics in the helpers can overflow and would then result to skip the cache cleaning/invalidation. Therefore there is no guarantee when all the writes will reach the memory. This undefined behavior was meant to be addressed by XSA-437, but the approach was not sufficient.

Buffer Overflow

[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE

CVE-2023-34325 7.8 - High - January 05, 2024

[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] libfsimage contains parsing code for several filesystems, most of them based on grub-legacy code. libfsimage is used by pygrub to inspect guest disks. Pygrub runs as the same user as the toolstack (root in a priviledged domain). At least one issue has been reported to the Xen Security Team that allows an attacker to trigger a stack buffer overflow in libfsimage. After further analisys the Xen Security Team is no longer confident in the suitability of libfsimage when run against guest controlled input with super user priviledges. In order to not affect current deployments that rely on pygrub patches are provided in the resolution section of the advisory that allow running pygrub in deprivileged mode. CVE-2023-4949 refers to the original issue in the upstream grub project ("An attacker with local access to a system (either through a disk or external drive) can present a modified XFS partition to grub-legacy in such a way to exploit a memory corruption in grubs XFS file system implementation.") CVE-2023-34325 refers specifically to the vulnerabilities in Xen's copy of libfsimage, which is decended from a very old version of grub.

Memory Corruption

The caching invalidation guidelines

CVE-2023-34326 7.8 - High - January 05, 2024

The caching invalidation guidelines from the AMD-Vi specification (48882Rev 3.07-PUBOct 2022) is incorrect on some hardware, as devices will malfunction (see stale DMA mappings) if some fields of the DTE are updated but the IOMMU TLB is not flushed. Such stale DMA mappings can point to memory ranges not owned by the guest, thus allowing access to unindented memory regions.

[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE

CVE-2023-34327 5.5 - Medium - January 05, 2024

[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] AMD CPUs since ~2014 have extensions to normal x86 debugging functionality. Xen supports guests using these extensions. Unfortunately there are errors in Xen's handling of the guest state, leading to denials of service. 1) CVE-2023-34327 - An HVM vCPU can end up operating in the context of a previous vCPUs debug mask state. 2) CVE-2023-34328 - A PV vCPU can place a breakpoint over the live GDT. This allows the PV vCPU to exploit XSA-156 / CVE-2015-8104 and lock up the CPU entirely.

[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE

CVE-2023-34328 5.5 - Medium - January 05, 2024

[This CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] AMD CPUs since ~2014 have extensions to normal x86 debugging functionality. Xen supports guests using these extensions. Unfortunately there are errors in Xen's handling of the guest state, leading to denials of service. 1) CVE-2023-34327 - An HVM vCPU can end up operating in the context of a previous vCPUs debug mask state. 2) CVE-2023-34328 - A PV vCPU can place a breakpoint over the live GDT. This allows the PV vCPU to exploit XSA-156 / CVE-2015-8104 and lock up the CPU entirely.

The current setup of the quarantine page tables assumes

CVE-2023-46835 5.5 - Medium - January 05, 2024

The current setup of the quarantine page tables assumes that the quarantine domain (dom_io) has been initialized with an address width of DEFAULT_DOMAIN_ADDRESS_WIDTH (48) and hence 4 page table levels. However dom_io being a PV domain gets the AMD-Vi IOMMU page tables levels based on the maximum (hot pluggable) RAM address, and hence on systems with no RAM above the 512GB mark only 3 page-table levels are configured in the IOMMU. On systems without RAM above the 512GB boundary amd_iommu_quarantine_init() will setup page tables for the scratch page with 4 levels, while the IOMMU will be configured to use 3 levels only, resulting in the last page table directory (PDE) effectively becoming a page table entry (PTE), and hence a device in quarantine mode gaining write access to the page destined to be a PDE. Due to this page table level mismatch, the sink page the device gets read/write access to is no longer cleared between device assignment, possibly leading to data leaks.

Cortex-A77 cores (r0p0 and r1p0) are affected by erratum 1508412 where software

CVE-2023-34320 5.5 - Medium - December 08, 2023

Cortex-A77 cores (r0p0 and r1p0) are affected by erratum 1508412 where software, under certain circumstances, could deadlock a core due to the execution of either a load to device or non-cacheable memory, and either a store exclusive or register read of the Physical Address Register (PAR_EL1) in close proximity.

Improper Locking

An attacker with local access to a system (either through a disk or external drive)

CVE-2023-4949 6.7 - Medium - November 10, 2023

An attacker with local access to a system (either through a disk or external drive) can present a modified XFS partition to grub-legacy in such a way to exploit a memory corruption in grubs XFS file system implementation.

Memory Corruption

The fix for XSA-423 added logic to Linux'es netback driver to deal with a frontend splitting a packet in a way such

CVE-2023-34319 7.8 - High - September 22, 2023

The fix for XSA-423 added logic to Linux'es netback driver to deal with a frontend splitting a packet in a way such that not all of the headers would come in one piece. Unfortunately the logic introduced there didn't account for the extreme case of the entire packet being split into as many pieces as permitted by the protocol, yet still being smaller than the area that's specially dealt with to keep all (possible) headers together. Such an unusual packet would therefore trigger a buffer overrun in the driver.

Memory Corruption

Information exposure through microarchitectural state after transient execution in certain vector execution units for some Intel(R) Processors may

CVE-2022-40982 6.5 - Medium - August 11, 2023

Information exposure through microarchitectural state after transient execution in certain vector execution units for some Intel(R) Processors may allow an authenticated user to potentially enable information disclosure via local access.

Side Channel Attack

A division-by-zero error on some AMD processors can potentially return speculative data resulting in loss of confidentiality

CVE-2023-20588 5.5 - Medium - August 08, 2023

A division-by-zero error on some AMD processors can potentially return speculative data resulting in loss of confidentiality. 

Divide By Zero

An issue in Zen 2 CPUs, under specific microarchitectural circumstances, may

CVE-2023-20593 5.5 - Medium - July 24, 2023

An issue in Zen 2 CPUs, under specific microarchitectural circumstances, may allow an attacker to potentially access sensitive information.

The AdSanity plugin for WordPress is vulnerable to arbitrary file uploads due to missing file type validation in the 'ajax_upload' function in versions up to

CVE-2022-4949 8.8 - High - June 07, 2023

The AdSanity plugin for WordPress is vulnerable to arbitrary file uploads due to missing file type validation in the 'ajax_upload' function in versions up to, and including, 1.8.1. This makes it possible for authenticated attackers with Contributor+ level privileges to upload arbitrary files on the affected sites server which makes remote code execution possible.

Unrestricted File Upload

Mishandling of guest SSBD selection on AMD hardware The current logic to set SSBD on AMD Family 17h and Hygon Family 18h processors requires

CVE-2022-42336 3.3 - Low - May 17, 2023

Mishandling of guest SSBD selection on AMD hardware The current logic to set SSBD on AMD Family 17h and Hygon Family 18h processors requires that the setting of SSBD is coordinated at a core level, as the setting is shared between threads. Logic was introduced to keep track of how many threads require SSBD active in order to coordinate it, such logic relies on using a per-core counter of threads that have SSBD active. When running on the mentioned hardware, it's possible for a guest to under or overflow the thread counter, because each write to VIRT_SPEC_CTRL.SSBD by the guest gets propagated to the helper that does the per-core active accounting. Underflowing the counter causes the value to get saturated, and thus attempts for guests running on the same core to set SSBD won't have effect because the hypervisor assumes it's already active.

x86 shadow paging arbitrary pointer dereference In environments where host assisted address translation is necessary but Hardware Assisted Paging (HAP) is unavailable

CVE-2022-42335 7.8 - High - April 25, 2023

x86 shadow paging arbitrary pointer dereference In environments where host assisted address translation is necessary but Hardware Assisted Paging (HAP) is unavailable, Xen will run guests in so called shadow mode. Due to too lax a check in one of the hypervisor routines used for shadow page handling it is possible for a guest with a PCI device passed through to cause the hypervisor to access an arbitrary pointer partially under guest control.

NULL Pointer Dereference

x86 shadow plus log-dirty mode use-after-free In environments where host assisted address translation is necessary but Hardware Assisted Paging (HAP) is unavailable

CVE-2022-42332 7.8 - High - March 21, 2023

x86 shadow plus log-dirty mode use-after-free In environments where host assisted address translation is necessary but Hardware Assisted Paging (HAP) is unavailable, Xen will run guests in so called shadow mode. Shadow mode maintains a pool of memory used for both shadow page tables as well as auxiliary data structures. To migrate or snapshot guests, Xen additionally runs them in so called log-dirty mode. The data structures needed by the log-dirty tracking are part of aformentioned auxiliary data. In order to keep error handling efforts within reasonable bounds, for operations which may require memory allocations shadow mode logic ensures up front that enough memory is available for the worst case requirements. Unfortunately, while page table memory is properly accounted for on the code path requiring the potential establishing of new shadows, demands by the log-dirty infrastructure were not taken into consideration. As a result, just established shadow page tables could be freed again immediately, while other code is still accessing them on the assumption that they would remain allocated.

Dangling pointer

x86/HVM pinned cache attributes mis-handling T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42333 8.6 - High - March 21, 2023

x86/HVM pinned cache attributes mis-handling T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] To allow cachability control for HVM guests with passed through devices, an interface exists to explicitly override defaults which would otherwise be put in place. While not exposed to the affected guests themselves, the interface specifically exists for domains controlling such guests. This interface may therefore be used by not fully privileged entities, e.g. qemu running deprivileged in Dom0 or qemu running in a so called stub-domain. With this exposure it is an issue that - the number of the such controlled regions was unbounded (CVE-2022-42333), - installation and removal of such regions was not properly serialized (CVE-2022-42334).

Allocation of Resources Without Limits or Throttling

x86/HVM pinned cache attributes mis-handling T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42334 6.5 - Medium - March 21, 2023

x86/HVM pinned cache attributes mis-handling T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] To allow cachability control for HVM guests with passed through devices, an interface exists to explicitly override defaults which would otherwise be put in place. While not exposed to the affected guests themselves, the interface specifically exists for domains controlling such guests. This interface may therefore be used by not fully privileged entities, e.g. qemu running deprivileged in Dom0 or qemu running in a so called stub-domain. With this exposure it is an issue that - the number of the such controlled regions was unbounded (CVE-2022-42333), - installation and removal of such regions was not properly serialized (CVE-2022-42334).

Allocation of Resources Without Limits or Throttling

x86: speculative vulnerability in 32bit SYSCALL path Due to an oversight in the very original Spectre/Meltdown security work (XSA-254)

CVE-2022-42331 5.5 - Medium - March 21, 2023

x86: speculative vulnerability in 32bit SYSCALL path Due to an oversight in the very original Spectre/Meltdown security work (XSA-254), one entrypath performs its speculation-safety actions too late. In some configurations, there is an unprotected RET instruction which can be attacked with a variety of speculative attacks.

Guests can cause Xenstore crash via soft reset When a guest issues a "Soft Reset" (e.g

CVE-2022-42330 7.5 - High - January 26, 2023

Guests can cause Xenstore crash via soft reset When a guest issues a "Soft Reset" (e.g. for performing a kexec) the libxl based Xen toolstack will normally perform a XS_RELEASE Xenstore operation. Due to a bug in xenstored this can result in a crash of xenstored. Any other use of XS_RELEASE will have the same impact.

Xenstore: Cooperating guests can create arbitrary numbers of nodes T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42322 5.5 - Medium - November 01, 2022

Xenstore: Cooperating guests can create arbitrary numbers of nodes T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Since the fix of XSA-322 any Xenstore node owned by a removed domain will be modified to be owned by Dom0. This will allow two malicious guests working together to create an arbitrary number of Xenstore nodes. This is possible by domain A letting domain B write into domain A's local Xenstore tree. Domain B can then create many nodes and reboot. The nodes created by domain B will now be owned by Dom0. By repeating this process over and over again an arbitrary number of nodes can be created, as Dom0's number of nodes isn't limited by Xenstore quota.

Memory Leak

x86: unintended memory sharing between guests On Intel systems

CVE-2022-42327 7.1 - High - November 01, 2022

x86: unintended memory sharing between guests On Intel systems that support the "virtualize APIC accesses" feature, a guest can read and write the global shared xAPIC page by moving the local APIC out of xAPIC mode. Access to this shared page bypasses the expected isolation that should exist between two guests.

Xenstore: Cooperating guests can create arbitrary numbers of nodes T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42323 5.5 - Medium - November 01, 2022

Xenstore: Cooperating guests can create arbitrary numbers of nodes T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Since the fix of XSA-322 any Xenstore node owned by a removed domain will be modified to be owned by Dom0. This will allow two malicious guests working together to create an arbitrary number of Xenstore nodes. This is possible by domain A letting domain B write into domain A's local Xenstore tree. Domain B can then create many nodes and reboot. The nodes created by domain B will now be owned by Dom0. By repeating this process over and over again an arbitrary number of nodes can be created, as Dom0's number of nodes isn't limited by Xenstore quota.

Memory Leak

Oxenstored 32->31 bit integer truncation issues Integers in Ocaml are 63 or 31 bits of signed precision

CVE-2022-42324 5.5 - Medium - November 01, 2022

Oxenstored 32->31 bit integer truncation issues Integers in Ocaml are 63 or 31 bits of signed precision. The Ocaml Xenbus library takes a C uint32_t out of the ring and casts it directly to an Ocaml integer. In 64-bit Ocaml builds this is fine, but in 32-bit builds, it truncates off the most significant bit, and then creates unsigned/signed confusion in the remainder. This in turn can feed a negative value into logic not expecting a negative value, resulting in unexpected exceptions being thrown. The unexpected exception is not handled suitably, creating a busy-loop trying (and failing) to take the bad packet out of the xenstore ring.

Incorrect Conversion between Numeric Types

Xenstore: Guests can create arbitrary number of nodes

CVE-2022-42325 5.5 - Medium - November 01, 2022

Xenstore: Guests can create arbitrary number of nodes via transactions T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] In case a node has been created in a transaction and it is later deleted in the same transaction, the transaction will be terminated with an error. As this error is encountered only when handling the deleted node at transaction finalization, the transaction will have been performed partially and without updating the accounting information. This will enable a malicious guest to create arbitrary number of nodes.

Memory Leak

Xenstore: Guests can create arbitrary number of nodes

CVE-2022-42326 5.5 - Medium - November 01, 2022

Xenstore: Guests can create arbitrary number of nodes via transactions T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] In case a node has been created in a transaction and it is later deleted in the same transaction, the transaction will be terminated with an error. As this error is encountered only when handling the deleted node at transaction finalization, the transaction will have been performed partially and without updating the accounting information. This will enable a malicious guest to create arbitrary number of nodes.

Memory Leak

Xenstore: Guests can crash xenstored Due to a bug in the fix of XSA-115 a malicious guest can cause xenstored to use a wrong pointer during node creation in an error path

CVE-2022-42309 8.8 - High - November 01, 2022

Xenstore: Guests can crash xenstored Due to a bug in the fix of XSA-115 a malicious guest can cause xenstored to use a wrong pointer during node creation in an error path, resulting in a crash of xenstored or a memory corruption in xenstored causing further damage. Entering the error path can be controlled by the guest e.g. by exceeding the quota value of maximum nodes per domain.

Release of Invalid Pointer or Reference

Xenstore: Guests can create orphaned Xenstore nodes By creating multiple nodes inside a transaction resulting in an error

CVE-2022-42310 5.5 - Medium - November 01, 2022

Xenstore: Guests can create orphaned Xenstore nodes By creating multiple nodes inside a transaction resulting in an error, a malicious guest can create orphaned nodes in the Xenstore data base, as the cleanup after the error will not remove all nodes already created. When the transaction is committed after this situation, nodes without a valid parent can be made permanent in the data base.

Insufficient Cleanup

Xenstore: Guests can get access to Xenstore nodes of deleted domains Access rights of Xenstore nodes are per domid

CVE-2022-42320 7 - High - November 01, 2022

Xenstore: Guests can get access to Xenstore nodes of deleted domains Access rights of Xenstore nodes are per domid. When a domain is gone, there might be Xenstore nodes left with access rights containing the domid of the removed domain. This is normally no problem, as those access right entries will be corrected when such a node is written later. There is a small time window when a new domain is created, where the access rights of a past domain with the same domid as the new one will be regarded to be still valid, leading to the new domain being able to get access to a node which was meant to be accessible by the removed domain. For this to happen another domain needs to write the node before the newly created domain is being introduced to Xenstore by dom0.

Insufficient Cleanup

Xenstore: Guests can crash xenstored via exhausting the stack Xenstored is using recursion for some Xenstore operations (e.g

CVE-2022-42321 6.5 - Medium - November 01, 2022

Xenstore: Guests can crash xenstored via exhausting the stack Xenstored is using recursion for some Xenstore operations (e.g. for deleting a sub-tree of Xenstore nodes). With sufficiently deep nesting levels this can result in stack exhaustion on xenstored, leading to a crash of xenstored.

Stack Exhaustion

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42312 6.5 - Medium - November 01, 2022

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Malicious guests can cause xenstored to allocate vast amounts of memory, eventually resulting in a Denial of Service (DoS) of xenstored. There are multiple ways how guests can cause large memory allocations in xenstored: - - by issuing new requests to xenstored without reading the responses, causing the responses to be buffered in memory - - by causing large number of watch events to be generated via setting up multiple xenstore watches and then e.g. deleting many xenstore nodes below the watched path - - by creating as many nodes as allowed with the maximum allowed size and path length in as many transactions as possible - - by accessing many nodes inside a transaction

Allocation of Resources Without Limits or Throttling

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42313 6.5 - Medium - November 01, 2022

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Malicious guests can cause xenstored to allocate vast amounts of memory, eventually resulting in a Denial of Service (DoS) of xenstored. There are multiple ways how guests can cause large memory allocations in xenstored: - - by issuing new requests to xenstored without reading the responses, causing the responses to be buffered in memory - - by causing large number of watch events to be generated via setting up multiple xenstore watches and then e.g. deleting many xenstore nodes below the watched path - - by creating as many nodes as allowed with the maximum allowed size and path length in as many transactions as possible - - by accessing many nodes inside a transaction

Allocation of Resources Without Limits or Throttling

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42314 6.5 - Medium - November 01, 2022

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Malicious guests can cause xenstored to allocate vast amounts of memory, eventually resulting in a Denial of Service (DoS) of xenstored. There are multiple ways how guests can cause large memory allocations in xenstored: - - by issuing new requests to xenstored without reading the responses, causing the responses to be buffered in memory - - by causing large number of watch events to be generated via setting up multiple xenstore watches and then e.g. deleting many xenstore nodes below the watched path - - by creating as many nodes as allowed with the maximum allowed size and path length in as many transactions as possible - - by accessing many nodes inside a transaction

Allocation of Resources Without Limits or Throttling

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42315 6.5 - Medium - November 01, 2022

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Malicious guests can cause xenstored to allocate vast amounts of memory, eventually resulting in a Denial of Service (DoS) of xenstored. There are multiple ways how guests can cause large memory allocations in xenstored: - - by issuing new requests to xenstored without reading the responses, causing the responses to be buffered in memory - - by causing large number of watch events to be generated via setting up multiple xenstore watches and then e.g. deleting many xenstore nodes below the watched path - - by creating as many nodes as allowed with the maximum allowed size and path length in as many transactions as possible - - by accessing many nodes inside a transaction

Allocation of Resources Without Limits or Throttling

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42316 6.5 - Medium - November 01, 2022

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Malicious guests can cause xenstored to allocate vast amounts of memory, eventually resulting in a Denial of Service (DoS) of xenstored. There are multiple ways how guests can cause large memory allocations in xenstored: - - by issuing new requests to xenstored without reading the responses, causing the responses to be buffered in memory - - by causing large number of watch events to be generated via setting up multiple xenstore watches and then e.g. deleting many xenstore nodes below the watched path - - by creating as many nodes as allowed with the maximum allowed size and path length in as many transactions as possible - - by accessing many nodes inside a transaction

Allocation of Resources Without Limits or Throttling

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42317 6.5 - Medium - November 01, 2022

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Malicious guests can cause xenstored to allocate vast amounts of memory, eventually resulting in a Denial of Service (DoS) of xenstored. There are multiple ways how guests can cause large memory allocations in xenstored: - - by issuing new requests to xenstored without reading the responses, causing the responses to be buffered in memory - - by causing large number of watch events to be generated via setting up multiple xenstore watches and then e.g. deleting many xenstore nodes below the watched path - - by creating as many nodes as allowed with the maximum allowed size and path length in as many transactions as possible - - by accessing many nodes inside a transaction

Allocation of Resources Without Limits or Throttling

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42318 6.5 - Medium - November 01, 2022

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Malicious guests can cause xenstored to allocate vast amounts of memory, eventually resulting in a Denial of Service (DoS) of xenstored. There are multiple ways how guests can cause large memory allocations in xenstored: - - by issuing new requests to xenstored without reading the responses, causing the responses to be buffered in memory - - by causing large number of watch events to be generated via setting up multiple xenstore watches and then e.g. deleting many xenstore nodes below the watched path - - by creating as many nodes as allowed with the maximum allowed size and path length in as many transactions as possible - - by accessing many nodes inside a transaction

Allocation of Resources Without Limits or Throttling

Xenstore: Guests can cause Xenstore to not free temporary memory When working on a request of a guest

CVE-2022-42319 6.5 - Medium - November 01, 2022

Xenstore: Guests can cause Xenstore to not free temporary memory When working on a request of a guest, xenstored might need to allocate quite large amounts of memory temporarily. This memory is freed only after the request has been finished completely. A request is regarded to be finished only after the guest has read the response message of the request from the ring page. Thus a guest not reading the response can cause xenstored to not free the temporary memory. This can result in memory shortages causing Denial of Service (DoS) of xenstored.

Memory Leak

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-42311 6.5 - Medium - November 01, 2022

Xenstore: guests can let run xenstored out of memory T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Malicious guests can cause xenstored to allocate vast amounts of memory, eventually resulting in a Denial of Service (DoS) of xenstored. There are multiple ways how guests can cause large memory allocations in xenstored: - - by issuing new requests to xenstored without reading the responses, causing the responses to be buffered in memory - - by causing large number of watch events to be generated via setting up multiple xenstore watches and then e.g. deleting many xenstore nodes below the watched path - - by creating as many nodes as allowed with the maximum allowed size and path length in as many transactions as possible - - by accessing many nodes inside a transaction

Allocation of Resources Without Limits or Throttling

P2M pool freeing may take excessively long The P2M pool backing second level address translation for guests may be of significant size

CVE-2022-33746 6.5 - Medium - October 11, 2022

P2M pool freeing may take excessively long The P2M pool backing second level address translation for guests may be of significant size. Therefore its freeing may take more time than is reasonable without intermediate preemption checks. Such checking for the need to preempt was so far missing.

Improper Resource Shutdown or Release

Arm: unbounded memory consumption for 2nd-level page tables Certain actions require e.g

CVE-2022-33747 3.8 - Low - October 11, 2022

Arm: unbounded memory consumption for 2nd-level page tables Certain actions require e.g. removing pages from a guest's P2M (Physical-to-Machine) mapping. When large pages are in use to map guest pages in the 2nd-stage page tables, such a removal operation may incur a memory allocation (to replace a large mapping with individual smaller ones). These memory allocations are taken from the global memory pool. A malicious guest might be able to cause the global memory pool to be exhausted by manipulating its own P2M mappings.

Improper Resource Shutdown or Release

lock order inversion in transitive grant copy handling As part of XSA-226 a missing cleanup call was inserted on an error handling path

CVE-2022-33748 5.6 - Medium - October 11, 2022

lock order inversion in transitive grant copy handling As part of XSA-226 a missing cleanup call was inserted on an error handling path. While doing so, locking requirements were not paid attention to. As a result two cooperating guests granting each other transitive grants can cause locks to be acquired nested within one another, but in respectively opposite order. With suitable timing between the involved grant copy operations this may result in the locking up of a CPU.

Improper Handling of Exceptional Conditions

insufficient TLB flush for x86 PV guests in shadow mode For migration as well as to work around kernels unaware of L1TF (see XSA-273)

CVE-2022-33745 8.8 - High - July 26, 2022

insufficient TLB flush for x86 PV guests in shadow mode For migration as well as to work around kernels unaware of L1TF (see XSA-273), PV guests may be run in shadow paging mode. To address XSA-401, code was moved inside a function in Xen. This code movement missed a variable changing meaning / value between old and new code positions. The now wrong use of the variable did lead to a wrong TLB flush condition, omitting flushes where such are necessary.

Intel microprocessor generations 6 to 8 are affected by a new Spectre variant

CVE-2022-29901 6.5 - Medium - July 12, 2022

Intel microprocessor generations 6 to 8 are affected by a new Spectre variant that is able to bypass their retpoline mitigation in the kernel to leak arbitrary data. An attacker with unprivileged user access can hijack return instructions to achieve arbitrary speculative code execution under certain microarchitecture-dependent conditions.

Exposure of Resource to Wrong Sphere

Mis-trained branch predictions for return instructions may

CVE-2022-29900 6.5 - Medium - July 12, 2022

Mis-trained branch predictions for return instructions may allow arbitrary speculative code execution under certain microarchitecture-dependent conditions.

Improper Removal of Sensitive Information Before Storage or Transfer

Linux disk/nic frontends data leaks T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-26365 7.1 - High - July 05, 2022

Linux disk/nic frontends data leaks T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Linux Block and Network PV device frontends don't zero memory regions before sharing them with the backend (CVE-2022-26365, CVE-2022-33740). Additionally the granularity of the grant table doesn't allow sharing less than a 4K page, leading to unrelated data residing in the same 4K page as data shared with a backend being accessible by such backend (CVE-2022-33741, CVE-2022-33742).

Memory Leak

Linux disk/nic frontends data leaks T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-33740 7.1 - High - July 05, 2022

Linux disk/nic frontends data leaks T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Linux Block and Network PV device frontends don't zero memory regions before sharing them with the backend (CVE-2022-26365, CVE-2022-33740). Additionally the granularity of the grant table doesn't allow sharing less than a 4K page, leading to unrelated data residing in the same 4K page as data shared with a backend being accessible by such backend (CVE-2022-33741, CVE-2022-33742).

Improper Removal of Sensitive Information Before Storage or Transfer

Linux disk/nic frontends data leaks T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-33741 7.1 - High - July 05, 2022

Linux disk/nic frontends data leaks T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Linux Block and Network PV device frontends don't zero memory regions before sharing them with the backend (CVE-2022-26365, CVE-2022-33740). Additionally the granularity of the grant table doesn't allow sharing less than a 4K page, leading to unrelated data residing in the same 4K page as data shared with a backend being accessible by such backend (CVE-2022-33741, CVE-2022-33742).

Information Disclosure

Linux disk/nic frontends data leaks T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-33742 7.1 - High - July 05, 2022

Linux disk/nic frontends data leaks T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Linux Block and Network PV device frontends don't zero memory regions before sharing them with the backend (CVE-2022-26365, CVE-2022-33740). Additionally the granularity of the grant table doesn't allow sharing less than a 4K page, leading to unrelated data residing in the same 4K page as data shared with a backend being accessible by such backend (CVE-2022-33741, CVE-2022-33742).

Information Disclosure

network backend may cause Linux netfront to use freed SKBs While adding logic to support XDP (eXpress Data Path), a code label was moved in a way

CVE-2022-33743 7.8 - High - July 05, 2022

network backend may cause Linux netfront to use freed SKBs While adding logic to support XDP (eXpress Data Path), a code label was moved in a way allowing for SKBs having references (pointers) retained for further processing to nevertheless be freed.

Incomplete cleanup in specific special register write operations for some Intel(R) Processors may

CVE-2022-21166 5.5 - Medium - June 15, 2022

Incomplete cleanup in specific special register write operations for some Intel(R) Processors may allow an authenticated user to potentially enable information disclosure via local access.

Insufficient Cleanup

Incomplete cleanup of microarchitectural fill buffers on some Intel(R) Processors may

CVE-2022-21125 5.5 - Medium - June 15, 2022

Incomplete cleanup of microarchitectural fill buffers on some Intel(R) Processors may allow an authenticated user to potentially enable information disclosure via local access.

Insufficient Cleanup

Incomplete cleanup in specific special register read operations for some Intel(R) Processors may

CVE-2022-21127 5.5 - Medium - June 15, 2022

Incomplete cleanup in specific special register read operations for some Intel(R) Processors may allow an authenticated user to potentially enable information disclosure via local access.

Insufficient Cleanup

Incomplete cleanup of multi-core shared buffers for some Intel(R) Processors may

CVE-2022-21123 5.5 - Medium - June 15, 2022

Incomplete cleanup of multi-core shared buffers for some Intel(R) Processors may allow an authenticated user to potentially enable information disclosure via local access.

Insufficient Cleanup

x86 pv: Race condition in typeref acquisition Xen maintains a type reference count for pages, in addition to a regular reference count

CVE-2022-26362 6.4 - Medium - June 09, 2022

x86 pv: Race condition in typeref acquisition Xen maintains a type reference count for pages, in addition to a regular reference count. This scheme is used to maintain invariants required for Xen's safety, e.g. PV guests may not have direct writeable access to pagetables; updates need auditing by Xen. Unfortunately, the logic for acquiring a type reference has a race condition, whereby a safely TLB flush is issued too early and creates a window where the guest can re-establish the read/write mapping before writeability is prohibited.

Race Condition

x86 pv: Insufficient care with non-coherent mappings T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-26363 6.7 - Medium - June 09, 2022

x86 pv: Insufficient care with non-coherent mappings T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Xen maintains a type reference count for pages, in addition to a regular reference count. This scheme is used to maintain invariants required for Xen's safety, e.g. PV guests may not have direct writeable access to pagetables; updates need auditing by Xen. Unfortunately, Xen's safety logic doesn't account for CPU-induced cache non-coherency; cases where the CPU can cause the content of the cache to be different to the content in main memory. In such cases, Xen's safety logic can incorrectly conclude that the contents of a page is safe.

x86 pv: Insufficient care with non-coherent mappings T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-26364 6.7 - Medium - June 09, 2022

x86 pv: Insufficient care with non-coherent mappings T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Xen maintains a type reference count for pages, in addition to a regular reference count. This scheme is used to maintain invariants required for Xen's safety, e.g. PV guests may not have direct writeable access to pagetables; updates need auditing by Xen. Unfortunately, Xen's safety logic doesn't account for CPU-induced cache non-coherency; cases where the CPU can cause the content of the cache to be different to the content in main memory. In such cases, Xen's safety logic can incorrectly conclude that the contents of a page is safe.

Racy interactions between dirty vram tracking and paging log dirty hypercalls Activation of log dirty mode done by XEN_DMOP_track_dirty_vram (was named HVMOP_track_dirty_vram before Xen 4.9) is racy with ongoing log dirty hypercalls

CVE-2022-26356 5.6 - Medium - April 05, 2022

Racy interactions between dirty vram tracking and paging log dirty hypercalls Activation of log dirty mode done by XEN_DMOP_track_dirty_vram (was named HVMOP_track_dirty_vram before Xen 4.9) is racy with ongoing log dirty hypercalls. A suitably timed call to XEN_DMOP_track_dirty_vram can enable log dirty while another CPU is still in the process of tearing down the structures related to a previously enabled log dirty mode (XEN_DOMCTL_SHADOW_OP_OFF). This is due to lack of mutually exclusive locking between both operations and can lead to entries being added in already freed slots, resulting in a memory leak.

Improper Locking

race in VT-d domain ID cleanup Xen domain IDs are up to 15 bits wide

CVE-2022-26357 7 - High - April 05, 2022

race in VT-d domain ID cleanup Xen domain IDs are up to 15 bits wide. VT-d hardware may allow for only less than 15 bits to hold a domain ID associating a physical device with a particular domain. Therefore internally Xen domain IDs are mapped to the smaller value range. The cleaning up of the housekeeping structures has a race, allowing for VT-d domain IDs to be leaked and flushes to be bypassed.

Race Condition

IOMMU: RMRR (VT-d) and unity map (AMD-Vi) handling issues T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-26358 7.8 - High - April 05, 2022

IOMMU: RMRR (VT-d) and unity map (AMD-Vi) handling issues T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Certain PCI devices in a system might be assigned Reserved Memory Regions (specified via Reserved Memory Region Reporting, "RMRR") for Intel VT-d or Unity Mapping ranges for AMD-Vi. These are typically used for platform tasks such as legacy USB emulation. Since the precise purpose of these regions is unknown, once a device associated with such a region is active, the mappings of these regions need to remain continuouly accessible by the device. This requirement has been violated. Subsequent DMA or interrupts from the device may have unpredictable behaviour, ranging from IOMMU faults to memory corruption.

IOMMU: RMRR (VT-d) and unity map (AMD-Vi) handling issues T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-26359 7.8 - High - April 05, 2022

IOMMU: RMRR (VT-d) and unity map (AMD-Vi) handling issues T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Certain PCI devices in a system might be assigned Reserved Memory Regions (specified via Reserved Memory Region Reporting, "RMRR") for Intel VT-d or Unity Mapping ranges for AMD-Vi. These are typically used for platform tasks such as legacy USB emulation. Since the precise purpose of these regions is unknown, once a device associated with such a region is active, the mappings of these regions need to remain continuouly accessible by the device. This requirement has been violated. Subsequent DMA or interrupts from the device may have unpredictable behaviour, ranging from IOMMU faults to memory corruption.

IOMMU: RMRR (VT-d) and unity map (AMD-Vi) handling issues T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-26360 7.8 - High - April 05, 2022

IOMMU: RMRR (VT-d) and unity map (AMD-Vi) handling issues T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Certain PCI devices in a system might be assigned Reserved Memory Regions (specified via Reserved Memory Region Reporting, "RMRR") for Intel VT-d or Unity Mapping ranges for AMD-Vi. These are typically used for platform tasks such as legacy USB emulation. Since the precise purpose of these regions is unknown, once a device associated with such a region is active, the mappings of these regions need to remain continuouly accessible by the device. This requirement has been violated. Subsequent DMA or interrupts from the device may have unpredictable behaviour, ranging from IOMMU faults to memory corruption.

IOMMU: RMRR (VT-d) and unity map (AMD-Vi) handling issues T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-26361 7.8 - High - April 05, 2022

IOMMU: RMRR (VT-d) and unity map (AMD-Vi) handling issues T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Certain PCI devices in a system might be assigned Reserved Memory Regions (specified via Reserved Memory Region Reporting, "RMRR") for Intel VT-d or Unity Mapping ranges for AMD-Vi. These are typically used for platform tasks such as legacy USB emulation. Since the precise purpose of these regions is unknown, once a device associated with such a region is active, the mappings of these regions need to remain continuouly accessible by the device. This requirement has been violated. Subsequent DMA or interrupts from the device may have unpredictable behaviour, ranging from IOMMU faults to memory corruption.

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-23040 7 - High - March 10, 2022

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Several Linux PV device frontends are using the grant table interfaces for removing access rights of the backends in ways being subject to race conditions, resulting in potential data leaks, data corruption by malicious backends, and denial of service triggered by malicious backends: blkfront, netfront, scsifront and the gntalloc driver are testing whether a grant reference is still in use. If this is not the case, they assume that a following removal of the granted access will always succeed, which is not true in case the backend has mapped the granted page between those two operations. As a result the backend can keep access to the memory page of the guest no matter how the page will be used after the frontend I/O has finished. The xenbus driver has a similar problem, as it doesn't check the success of removing the granted access of a shared ring buffer. blkfront: CVE-2022-23036 netfront: CVE-2022-23037 scsifront: CVE-2022-23038 gntalloc: CVE-2022-23039 xenbus: CVE-2022-23040 blkfront, netfront, scsifront, usbfront, dmabuf, xenbus, 9p, kbdfront, and pvcalls are using a functionality to delay freeing a grant reference until it is no longer in use, but the freeing of the related data page is not synchronized with dropping the granted access. As a result the backend can keep access to the memory page even after it has been freed and then re-used for a different purpose. CVE-2022-23041 netfront will fail a BUG_ON() assertion if it fails to revoke access in the rx path. This will result in a Denial of Service (DoS) situation of the guest which can be triggered by the backend. CVE-2022-23042

Race Condition

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-23042 7 - High - March 10, 2022

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Several Linux PV device frontends are using the grant table interfaces for removing access rights of the backends in ways being subject to race conditions, resulting in potential data leaks, data corruption by malicious backends, and denial of service triggered by malicious backends: blkfront, netfront, scsifront and the gntalloc driver are testing whether a grant reference is still in use. If this is not the case, they assume that a following removal of the granted access will always succeed, which is not true in case the backend has mapped the granted page between those two operations. As a result the backend can keep access to the memory page of the guest no matter how the page will be used after the frontend I/O has finished. The xenbus driver has a similar problem, as it doesn't check the success of removing the granted access of a shared ring buffer. blkfront: CVE-2022-23036 netfront: CVE-2022-23037 scsifront: CVE-2022-23038 gntalloc: CVE-2022-23039 xenbus: CVE-2022-23040 blkfront, netfront, scsifront, usbfront, dmabuf, xenbus, 9p, kbdfront, and pvcalls are using a functionality to delay freeing a grant reference until it is no longer in use, but the freeing of the related data page is not synchronized with dropping the granted access. As a result the backend can keep access to the memory page even after it has been freed and then re-used for a different purpose. CVE-2022-23041 netfront will fail a BUG_ON() assertion if it fails to revoke access in the rx path. This will result in a Denial of Service (DoS) situation of the guest which can be triggered by the backend. CVE-2022-23042

Race Condition

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-23041 7 - High - March 10, 2022

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Several Linux PV device frontends are using the grant table interfaces for removing access rights of the backends in ways being subject to race conditions, resulting in potential data leaks, data corruption by malicious backends, and denial of service triggered by malicious backends: blkfront, netfront, scsifront and the gntalloc driver are testing whether a grant reference is still in use. If this is not the case, they assume that a following removal of the granted access will always succeed, which is not true in case the backend has mapped the granted page between those two operations. As a result the backend can keep access to the memory page of the guest no matter how the page will be used after the frontend I/O has finished. The xenbus driver has a similar problem, as it doesn't check the success of removing the granted access of a shared ring buffer. blkfront: CVE-2022-23036 netfront: CVE-2022-23037 scsifront: CVE-2022-23038 gntalloc: CVE-2022-23039 xenbus: CVE-2022-23040 blkfront, netfront, scsifront, usbfront, dmabuf, xenbus, 9p, kbdfront, and pvcalls are using a functionality to delay freeing a grant reference until it is no longer in use, but the freeing of the related data page is not synchronized with dropping the granted access. As a result the backend can keep access to the memory page even after it has been freed and then re-used for a different purpose. CVE-2022-23041 netfront will fail a BUG_ON() assertion if it fails to revoke access in the rx path. This will result in a Denial of Service (DoS) situation of the guest which can be triggered by the backend. CVE-2022-23042

Race Condition

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-23039 7 - High - March 10, 2022

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Several Linux PV device frontends are using the grant table interfaces for removing access rights of the backends in ways being subject to race conditions, resulting in potential data leaks, data corruption by malicious backends, and denial of service triggered by malicious backends: blkfront, netfront, scsifront and the gntalloc driver are testing whether a grant reference is still in use. If this is not the case, they assume that a following removal of the granted access will always succeed, which is not true in case the backend has mapped the granted page between those two operations. As a result the backend can keep access to the memory page of the guest no matter how the page will be used after the frontend I/O has finished. The xenbus driver has a similar problem, as it doesn't check the success of removing the granted access of a shared ring buffer. blkfront: CVE-2022-23036 netfront: CVE-2022-23037 scsifront: CVE-2022-23038 gntalloc: CVE-2022-23039 xenbus: CVE-2022-23040 blkfront, netfront, scsifront, usbfront, dmabuf, xenbus, 9p, kbdfront, and pvcalls are using a functionality to delay freeing a grant reference until it is no longer in use, but the freeing of the related data page is not synchronized with dropping the granted access. As a result the backend can keep access to the memory page even after it has been freed and then re-used for a different purpose. CVE-2022-23041 netfront will fail a BUG_ON() assertion if it fails to revoke access in the rx path. This will result in a Denial of Service (DoS) situation of the guest which can be triggered by the backend. CVE-2022-23042

Race Condition

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-23038 7 - High - March 10, 2022

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Several Linux PV device frontends are using the grant table interfaces for removing access rights of the backends in ways being subject to race conditions, resulting in potential data leaks, data corruption by malicious backends, and denial of service triggered by malicious backends: blkfront, netfront, scsifront and the gntalloc driver are testing whether a grant reference is still in use. If this is not the case, they assume that a following removal of the granted access will always succeed, which is not true in case the backend has mapped the granted page between those two operations. As a result the backend can keep access to the memory page of the guest no matter how the page will be used after the frontend I/O has finished. The xenbus driver has a similar problem, as it doesn't check the success of removing the granted access of a shared ring buffer. blkfront: CVE-2022-23036 netfront: CVE-2022-23037 scsifront: CVE-2022-23038 gntalloc: CVE-2022-23039 xenbus: CVE-2022-23040 blkfront, netfront, scsifront, usbfront, dmabuf, xenbus, 9p, kbdfront, and pvcalls are using a functionality to delay freeing a grant reference until it is no longer in use, but the freeing of the related data page is not synchronized with dropping the granted access. As a result the backend can keep access to the memory page even after it has been freed and then re-used for a different purpose. CVE-2022-23041 netfront will fail a BUG_ON() assertion if it fails to revoke access in the rx path. This will result in a Denial of Service (DoS) situation of the guest which can be triggered by the backend. CVE-2022-23042

Race Condition

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-23037 7 - High - March 10, 2022

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Several Linux PV device frontends are using the grant table interfaces for removing access rights of the backends in ways being subject to race conditions, resulting in potential data leaks, data corruption by malicious backends, and denial of service triggered by malicious backends: blkfront, netfront, scsifront and the gntalloc driver are testing whether a grant reference is still in use. If this is not the case, they assume that a following removal of the granted access will always succeed, which is not true in case the backend has mapped the granted page between those two operations. As a result the backend can keep access to the memory page of the guest no matter how the page will be used after the frontend I/O has finished. The xenbus driver has a similar problem, as it doesn't check the success of removing the granted access of a shared ring buffer. blkfront: CVE-2022-23036 netfront: CVE-2022-23037 scsifront: CVE-2022-23038 gntalloc: CVE-2022-23039 xenbus: CVE-2022-23040 blkfront, netfront, scsifront, usbfront, dmabuf, xenbus, 9p, kbdfront, and pvcalls are using a functionality to delay freeing a grant reference until it is no longer in use, but the freeing of the related data page is not synchronized with dropping the granted access. As a result the backend can keep access to the memory page even after it has been freed and then re-used for a different purpose. CVE-2022-23041 netfront will fail a BUG_ON() assertion if it fails to revoke access in the rx path. This will result in a Denial of Service (DoS) situation of the guest which can be triggered by the backend. CVE-2022-23042

Race Condition

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains

CVE-2022-23036 7 - High - March 10, 2022

Linux PV device frontends vulnerable to attacks by backends T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Several Linux PV device frontends are using the grant table interfaces for removing access rights of the backends in ways being subject to race conditions, resulting in potential data leaks, data corruption by malicious backends, and denial of service triggered by malicious backends: blkfront, netfront, scsifront and the gntalloc driver are testing whether a grant reference is still in use. If this is not the case, they assume that a following removal of the granted access will always succeed, which is not true in case the backend has mapped the granted page between those two operations. As a result the backend can keep access to the memory page of the guest no matter how the page will be used after the frontend I/O has finished. The xenbus driver has a similar problem, as it doesn't check the success of removing the granted access of a shared ring buffer. blkfront: CVE-2022-23036 netfront: CVE-2022-23037 scsifront: CVE-2022-23038 gntalloc: CVE-2022-23039 xenbus: CVE-2022-23040 blkfront, netfront, scsifront, usbfront, dmabuf, xenbus, 9p, kbdfront, and pvcalls are using a functionality to delay freeing a grant reference until it is no longer in use, but the freeing of the related data page is not synchronized with dropping the granted access. As a result the backend can keep access to the memory page even after it has been freed and then re-used for a different purpose. CVE-2022-23041 netfront will fail a BUG_ON() assertion if it fails to revoke access in the rx path. This will result in a Denial of Service (DoS) situation of the guest which can be triggered by the backend. CVE-2022-23042

Race Condition

arm: guest_physmap_remove_page not removing the p2m mappings The functions to remove one or more entries

CVE-2022-23033 7.8 - High - January 25, 2022

arm: guest_physmap_remove_page not removing the p2m mappings The functions to remove one or more entries from a guest p2m pagetable on Arm (p2m_remove_mapping, guest_physmap_remove_page, and p2m_set_entry with mfn set to INVALID_MFN) do not actually clear the pagetable entry if the entry doesn't have the valid bit set. It is possible to have a valid pagetable entry without the valid bit set when a guest operating system uses set/way cache maintenance instructions. For instance, a guest issuing a set/way cache maintenance instruction, then calling the XENMEM_decrease_reservation hypercall to give back memory pages to Xen, might be able to retain access to those pages even after Xen started reusing them for other purposes.

Improper Resource Shutdown or Release

A PV guest could DoS Xen while unmapping a grant To address XSA-380, reference counting was introduced for grant mappings for the case where a PV guest

CVE-2022-23034 5.5 - Medium - January 25, 2022

A PV guest could DoS Xen while unmapping a grant To address XSA-380, reference counting was introduced for grant mappings for the case where a PV guest would have the IOMMU enabled. PV guests can request two forms of mappings. When both are in use for any individual mapping, unmapping of such a mapping can be requested in two steps. The reference count for such a mapping would then mistakenly be decremented twice. Underflow of the counters gets detected, resulting in the triggering of a hypervisor bug check.

Integer underflow

Insufficient cleanup of passed-through device IRQs The management of IRQs associated with physical devices exposed to x86 HVM guests involves an iterative operation in particular when cleaning up after the guest's use of the device

CVE-2022-23035 4.6 - Medium - January 25, 2022

Insufficient cleanup of passed-through device IRQs The management of IRQs associated with physical devices exposed to x86 HVM guests involves an iterative operation in particular when cleaning up after the guest's use of the device. In the case where an interrupt is not quiescent yet at the time this cleanup gets invoked, the cleanup attempt may be scheduled to be retried. When multiple interrupts are involved, this scheduling of a retry may get erroneously skipped. At the same time pointers may get cleared (resulting in a de-reference of NULL) and freed (resulting in a use-after-free), while other code would continue to assume them to be valid.

Insufficient Cleanup

Rogue backends can cause DoS of guests

CVE-2021-28711 6.5 - Medium - January 05, 2022

Rogue backends can cause DoS of guests via high frequency events T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Xen offers the ability to run PV backends in regular unprivileged guests, typically referred to as "driver domains". Running PV backends in driver domains has one primary security advantage: if a driver domain gets compromised, it doesn't have the privileges to take over the system. However, a malicious driver domain could try to attack other guests via sending events at a high frequency leading to a Denial of Service in the guest due to trying to service interrupts for elongated amounts of time. There are three affected backends: * blkfront patch 1, CVE-2021-28711 * netfront patch 2, CVE-2021-28712 * hvc_xen (console) patch 3, CVE-2021-28713

Rogue backends can cause DoS of guests

CVE-2021-28712 6.5 - Medium - January 05, 2022

Rogue backends can cause DoS of guests via high frequency events T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Xen offers the ability to run PV backends in regular unprivileged guests, typically referred to as "driver domains". Running PV backends in driver domains has one primary security advantage: if a driver domain gets compromised, it doesn't have the privileges to take over the system. However, a malicious driver domain could try to attack other guests via sending events at a high frequency leading to a Denial of Service in the guest due to trying to service interrupts for elongated amounts of time. There are three affected backends: * blkfront patch 1, CVE-2021-28711 * netfront patch 2, CVE-2021-28712 * hvc_xen (console) patch 3, CVE-2021-28713

Rogue backends can cause DoS of guests

CVE-2021-28713 6.5 - Medium - January 05, 2022

Rogue backends can cause DoS of guests via high frequency events T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Xen offers the ability to run PV backends in regular unprivileged guests, typically referred to as "driver domains". Running PV backends in driver domains has one primary security advantage: if a driver domain gets compromised, it doesn't have the privileges to take over the system. However, a malicious driver domain could try to attack other guests via sending events at a high frequency leading to a Denial of Service in the guest due to trying to service interrupts for elongated amounts of time. There are three affected backends: * blkfront patch 1, CVE-2021-28711 * netfront patch 2, CVE-2021-28712 * hvc_xen (console) patch 3, CVE-2021-28713

grant table v2 status pages may remain accessible after de-allocation (take two) Guest get permitted access to certain Xen-owned pages of memory

CVE-2021-28703 7 - High - December 07, 2021

grant table v2 status pages may remain accessible after de-allocation (take two) Guest get permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, get de-allocated when a guest switched (back) from v2 to v1. The freeing of such pages requires that the hypervisor know where in the guest these pages were mapped. The hypervisor tracks only one use within guest space, but racing requests from the guest to insert mappings of these pages may result in any of them to become mapped in multiple locations. Upon switching back from v2 to v1, the guest would then retain access to a page that was freed and perhaps re-used for other purposes. This bug was fortuitously fixed by code cleanup in Xen 4.14, and backported to security-supported Xen branches as a prerequisite of the fix for XSA-378.

issues with partially successful P2M updates on x86 T[his CNA information record relates to multiple CVEs; the text explains

CVE-2021-28705 7.8 - High - November 24, 2021

issues with partially successful P2M updates on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] x86 HVM and PVH guests may be started in populate-on-demand (PoD) mode, to provide a way for them to later easily have more memory assigned. Guests are permitted to control certain P2M aspects of individual pages via hypercalls. These hypercalls may act on ranges of pages specified via page orders (resulting in a power-of-2 number of pages). In some cases the hypervisor carries out the requests by splitting them into smaller chunks. Error handling in certain PoD cases has been insufficient in that in particular partial success of some operations was not properly accounted for. There are two code paths affected - page removal (CVE-2021-28705) and insertion of new pages (CVE-2021-28709). (We provide one patch which combines the fix to both issues.)

Improper Handling of Exceptional Conditions

issues with partially successful P2M updates on x86 T[his CNA information record relates to multiple CVEs; the text explains

CVE-2021-28709 7.8 - High - November 24, 2021

issues with partially successful P2M updates on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] x86 HVM and PVH guests may be started in populate-on-demand (PoD) mode, to provide a way for them to later easily have more memory assigned. Guests are permitted to control certain P2M aspects of individual pages via hypercalls. These hypercalls may act on ranges of pages specified via page orders (resulting in a power-of-2 number of pages). In some cases the hypervisor carries out the requests by splitting them into smaller chunks. Error handling in certain PoD cases has been insufficient in that in particular partial success of some operations was not properly accounted for. There are two code paths affected - page removal (CVE-2021-28705) and insertion of new pages (CVE-2021-28709). (We provide one patch which combines the fix to both issues.)

Improper Handling of Exceptional Conditions

guests may exceed their designated memory limit When a guest is permitted to have close to 16TiB of memory

CVE-2021-28706 8.6 - High - November 24, 2021

guests may exceed their designated memory limit When a guest is permitted to have close to 16TiB of memory, it may be able to issue hypercalls to increase its memory allocation beyond the administrator established limit. This is a result of a calculation done with 32-bit precision, which may overflow. It would then only be the overflowed (and hence small) number which gets compared against the established upper bound.

Allocation of Resources Without Limits or Throttling

PoD operations on misaligned GFNs T[his CNA information record relates to multiple CVEs; the text explains

CVE-2021-28704 8.8 - High - November 24, 2021

PoD operations on misaligned GFNs T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] x86 HVM and PVH guests may be started in populate-on-demand (PoD) mode, to provide a way for them to later easily have more memory assigned. Guests are permitted to control certain P2M aspects of individual pages via hypercalls. These hypercalls may act on ranges of pages specified via page orders (resulting in a power-of-2 number of pages). The implementation of some of these hypercalls for PoD does not enforce the base page frame number to be suitably aligned for the specified order, yet some code involved in PoD handling actually makes such an assumption. These operations are XENMEM_decrease_reservation (CVE-2021-28704) and XENMEM_populate_physmap (CVE-2021-28707), the latter usable only by domains controlling the guest, i.e. a de-privileged qemu or a stub domain. (Patch 1, combining the fix to both these two issues.) In addition handling of XENMEM_decrease_reservation can also trigger a host crash when the specified page order is neither 4k nor 2M nor 1G (CVE-2021-28708, patch 2).

PoD operations on misaligned GFNs T[his CNA information record relates to multiple CVEs; the text explains

CVE-2021-28707 8.8 - High - November 24, 2021

PoD operations on misaligned GFNs T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] x86 HVM and PVH guests may be started in populate-on-demand (PoD) mode, to provide a way for them to later easily have more memory assigned. Guests are permitted to control certain P2M aspects of individual pages via hypercalls. These hypercalls may act on ranges of pages specified via page orders (resulting in a power-of-2 number of pages). The implementation of some of these hypercalls for PoD does not enforce the base page frame number to be suitably aligned for the specified order, yet some code involved in PoD handling actually makes such an assumption. These operations are XENMEM_decrease_reservation (CVE-2021-28704) and XENMEM_populate_physmap (CVE-2021-28707), the latter usable only by domains controlling the guest, i.e. a de-privileged qemu or a stub domain. (Patch 1, combining the fix to both these two issues.) In addition handling of XENMEM_decrease_reservation can also trigger a host crash when the specified page order is neither 4k nor 2M nor 1G (CVE-2021-28708, patch 2).

PoD operations on misaligned GFNs T[his CNA information record relates to multiple CVEs; the text explains

CVE-2021-28708 8.8 - High - November 24, 2021

PoD operations on misaligned GFNs T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] x86 HVM and PVH guests may be started in populate-on-demand (PoD) mode, to provide a way for them to later easily have more memory assigned. Guests are permitted to control certain P2M aspects of individual pages via hypercalls. These hypercalls may act on ranges of pages specified via page orders (resulting in a power-of-2 number of pages). The implementation of some of these hypercalls for PoD does not enforce the base page frame number to be suitably aligned for the specified order, yet some code involved in PoD handling actually makes such an assumption. These operations are XENMEM_decrease_reservation (CVE-2021-28704) and XENMEM_populate_physmap (CVE-2021-28707), the latter usable only by domains controlling the guest, i.e. a de-privileged qemu or a stub domain. (Patch 1, combining the fix to both these two issues.) In addition handling of XENMEM_decrease_reservation can also trigger a host crash when the specified page order is neither 4k nor 2M nor 1G (CVE-2021-28708, patch 2).

certain VT-d IOMMUs may not work in shared page table mode For efficiency reasons

CVE-2021-28710 8.8 - High - November 21, 2021

certain VT-d IOMMUs may not work in shared page table mode For efficiency reasons, address translation control structures (page tables) may (and, on suitable hardware, by default will) be shared between CPUs, for second-level translation (EPT), and IOMMUs. These page tables are presently set up to always be 4 levels deep. However, an IOMMU may require the use of just 3 page table levels. In such a configuration the lop level table needs to be stripped before inserting the root table's address into the hardware pagetable base register. When sharing page tables, Xen erroneously skipped this stripping. Consequently, the guest is able to write to leaf page table entries.

Improper Privilege Management

PCI devices with RMRRs not deassigned correctly Certain PCI devices in a system might be assigned Reserved Memory Regions (specified

CVE-2021-28702 7.6 - High - October 06, 2021

PCI devices with RMRRs not deassigned correctly Certain PCI devices in a system might be assigned Reserved Memory Regions (specified via Reserved Memory Region Reporting, "RMRR"). These are typically used for platform tasks such as legacy USB emulation. If such a device is passed through to a guest, then on guest shutdown the device is not properly deassigned. The IOMMU configuration for these devices which are not properly deassigned ends up pointing to a freed data structure, including the IO Pagetables. Subsequent DMA or interrupts from the device will have unpredictable behaviour, ranging from IOMMU faults to memory corruption.

Improper Privilege Management

Another race in XENMAPSPACE_grant_table handling Guests are permitted access to certain Xen-owned pages of memory

CVE-2021-28701 7.8 - High - September 08, 2021

Another race in XENMAPSPACE_grant_table handling Guests are permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, are de-allocated when a guest switches (back) from v2 to v1. Freeing such pages requires that the hypervisor enforce that no parallel request can result in the addition of a mapping of such a page to a guest. That enforcement was missing, allowing guests to retain access to pages that were freed and perhaps re-used for other purposes. Unfortunately, when XSA-379 was being prepared, this similar issue was not noticed.

Race Condition

xen/arm: No memory limit for dom0less domUs The dom0less feature

CVE-2021-28700 4.9 - Medium - August 27, 2021

xen/arm: No memory limit for dom0less domUs The dom0less feature allows an administrator to create multiple unprivileged domains directly from Xen. Unfortunately, the memory limit from them is not set. This allow a domain to allocate memory beyond what an administrator originally configured.

Allocation of Resources Without Limits or Throttling

inadequate grant-v2 status frames array bounds check The v2 grant table interface separates grant attributes from grant status

CVE-2021-28699 5.5 - Medium - August 27, 2021

inadequate grant-v2 status frames array bounds check The v2 grant table interface separates grant attributes from grant status. That is, when operating in this mode, a guest has two tables. As a result, guests also need to be able to retrieve the addresses that the new status tracking table can be accessed through. For 32-bit guests on x86, translation of requests has to occur because the interface structure layouts commonly differ between 32- and 64-bit. The translation of the request to obtain the frame numbers of the grant status table involves translating the resulting array of frame numbers. Since the space used to carry out the translation is limited, the translation layer tells the core function the capacity of the array within translation space. Unfortunately the core function then only enforces array bounds to be below 8 times the specified value, and would write past the available space if enough frame numbers needed storing.

long running loops in grant table handling In order to properly monitor resource use

CVE-2021-28698 5.5 - Medium - August 27, 2021

long running loops in grant table handling In order to properly monitor resource use, Xen maintains information on the grant mappings a domain may create to map grants offered by other domains. In the process of carrying out certain actions, Xen would iterate over all such entries, including ones which aren't in use anymore and some which may have been created but never used. If the number of entries for a given domain is large enough, this iterating of the entire table may tie up a CPU for too long, starving other domains or causing issues in the hypervisor itself. Note that a domain may map its own grants, i.e. there is no need for multiple domains to be involved here. A pair of "cooperating" guests may, however, cause the effects to be more severe.

Infinite Loop

IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains

CVE-2021-28694 6.8 - Medium - August 27, 2021

IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Both AMD and Intel allow ACPI tables to specify regions of memory which should be left untranslated, which typically means these addresses should pass the translation phase unaltered. While these are typically device specific ACPI properties, they can also be specified to apply to a range of devices, or even all devices. On all systems with such regions Xen failed to prevent guests from undoing/replacing such mappings (CVE-2021-28694). On AMD systems, where a discontinuous range is specified by firmware, the supposedly-excluded middle range will also be identity-mapped (CVE-2021-28695). Further, on AMD systems, upon de-assigment of a physical device from a guest, the identity mappings would be left in place, allowing a guest continued access to ranges of memory which it shouldn't have access to anymore (CVE-2021-28696).

IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains

CVE-2021-28695 6.8 - Medium - August 27, 2021

IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Both AMD and Intel allow ACPI tables to specify regions of memory which should be left untranslated, which typically means these addresses should pass the translation phase unaltered. While these are typically device specific ACPI properties, they can also be specified to apply to a range of devices, or even all devices. On all systems with such regions Xen failed to prevent guests from undoing/replacing such mappings (CVE-2021-28694). On AMD systems, where a discontinuous range is specified by firmware, the supposedly-excluded middle range will also be identity-mapped (CVE-2021-28695). Further, on AMD systems, upon de-assigment of a physical device from a guest, the identity mappings would be left in place, allowing a guest continued access to ranges of memory which it shouldn't have access to anymore (CVE-2021-28696).

grant table v2 status pages may remain accessible after de-allocation Guest get permitted access to certain Xen-owned pages of memory

CVE-2021-28697 7.8 - High - August 27, 2021

grant table v2 status pages may remain accessible after de-allocation Guest get permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, get de-allocated when a guest switched (back) from v2 to v1. The freeing of such pages requires that the hypervisor know where in the guest these pages were mapped. The hypervisor tracks only one use within guest space, but racing requests from the guest to insert mappings of these pages may result in any of them to become mapped in multiple locations. Upon switching back from v2 to v1, the guest would then retain access to a page that was freed and perhaps re-used for other purposes.

Race Condition

IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains

CVE-2021-28696 6.8 - Medium - August 27, 2021

IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Both AMD and Intel allow ACPI tables to specify regions of memory which should be left untranslated, which typically means these addresses should pass the translation phase unaltered. While these are typically device specific ACPI properties, they can also be specified to apply to a range of devices, or even all devices. On all systems with such regions Xen failed to prevent guests from undoing/replacing such mappings (CVE-2021-28694). On AMD systems, where a discontinuous range is specified by firmware, the supposedly-excluded middle range will also be identity-mapped (CVE-2021-28695). Further, on AMD systems, upon de-assigment of a physical device from a guest, the identity mappings would be left in place, allowing a guest continued access to ranges of memory which it shouldn't have access to anymore (CVE-2021-28696).

AuthZ