KVM x86: Ignore -EBUSY for nested events in vcpu_block
CVE-2026-43265 Published on May 6, 2026
KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block()
In the Linux kernel, the following vulnerability has been resolved:
KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block()
Ignore -EBUSY when checking nested events after exiting a blocking state
while L2 is active, as exiting to userspace will generate a spurious
userspace exit, usually with KVM_EXIT_UNKNOWN, and likely lead to the VM's
demise. Continuing with the wakeup isn't perfect either, as *something*
has gone sideways if a vCPU is awakened in L2 with an injected event (or
worse, a nested run pending), but continuing on gives the VM a decent
chance of surviving without any major side effects.
As explained in the Fixes commits, it _should_ be impossible for a vCPU to
be put into a blocking state with an already-injected event (exception,
IRQ, or NMI). Unfortunately, userspace can stuff MP_STATE and/or injected
events, and thus put the vCPU into what should be an impossible state.
Don't bother trying to preserve the WARN, e.g. with an anti-syzkaller
Kconfig, as WARNs can (hopefully) be added in paths where _KVM_ would be
violating x86 architecture, e.g. by WARNing if KVM attempts to inject an
exception or interrupt while the vCPU isn't running.
Products Associated with CVE-2026-43265
Want to know whenever a new CVE is published for Linux Kernel? stack.watch will email you.
Affected Versions
Linux:- Version 26844fee6adee9b1557d2279b0506285de9ee82b and below 78265cd066d73a5cb41c088fcae4a2515e480d97 is affected.
- Version 26844fee6adee9b1557d2279b0506285de9ee82b and below ec3be7dc9391085a2d96700e159d66d1328b7ff6 is affected.
- Version 26844fee6adee9b1557d2279b0506285de9ee82b and below 2657439265d34a911886b916ba8be97ecc117d51 is affected.
- Version 26844fee6adee9b1557d2279b0506285de9ee82b and below 1e88b5f854bdb469424132e0bb44793ad7a7c20a is affected.
- Version 26844fee6adee9b1557d2279b0506285de9ee82b and below 1c957773063ed3264953597e32990a748381caf6 is affected.
- Version 26844fee6adee9b1557d2279b0506285de9ee82b and below ead63640d4e72e6f6d464f4e31f7fecb79af8869 is affected.
- Version 6.1 is affected.
- Before 6.1 is unaffected.
- Version 6.1.167, <= 6.1.* is unaffected.
- Version 6.6.130, <= 6.6.* is unaffected.
- Version 6.12.77, <= 6.12.* is unaffected.
- Version 6.18.17, <= 6.18.* is unaffected.
- Version 6.19.6, <= 6.19.* is unaffected.
- Version 7.0, <= * is unaffected.