Linux Kernel: EFI BS Memory Leak via memblock_free_late misuse
CVE-2026-23352 Published on March 25, 2026
x86/efi: defer freeing of boot services memory
In the Linux kernel, the following vulnerability has been resolved:
x86/efi: defer freeing of boot services memory
efi_free_boot_services() frees memory occupied by EFI_BOOT_SERVICES_CODE
and EFI_BOOT_SERVICES_DATA using memblock_free_late().
There are two issue with that: memblock_free_late() should be used for
memory allocated with memblock_alloc() while the memory reserved with
memblock_reserve() should be freed with free_reserved_area().
More acutely, with CONFIG_DEFERRED_STRUCT_PAGE_INIT=y
efi_free_boot_services() is called before deferred initialization of the
memory map is complete.
Benjamin Herrenschmidt reports that this causes a leak of ~140MB of
RAM on EC2 t3a.nano instances which only have 512MB or RAM.
If the freed memory resides in the areas that memory map for them is
still uninitialized, they won't be actually freed because
memblock_free_late() calls memblock_free_pages() and the latter skips
uninitialized pages.
Using free_reserved_area() at this point is also problematic because
__free_page() accesses the buddy of the freed page and that again might
end up in uninitialized part of the memory map.
Delaying the entire efi_free_boot_services() could be problematic
because in addition to freeing boot services memory it updates
efi.memmap without any synchronization and that's undesirable late in
boot when there is concurrency.
More robust approach is to only defer freeing of the EFI boot services
memory.
Split efi_free_boot_services() in two. First efi_unmap_boot_services()
collects ranges that should be freed into an array then
efi_free_boot_services() later frees them after deferred init is complete.
Products Associated with CVE-2026-23352
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Affected Versions
Linux:- Version 0aed459e8487eb6ebdb4efe8cefe1eafbc704b30 and below 4a2cb90c538f06c873a187aa743575d48685d7a6 is affected.
- Version 916f676f8dc016103f983c7ec54c18ecdbb6e349 and below 227688312fece0026fc67a00ba9a0b3611ebe95d is affected.
- Version 916f676f8dc016103f983c7ec54c18ecdbb6e349 and below 6a25e25279282c5c8ade554c04c6ab9dc7902c64 is affected.
- Version 916f676f8dc016103f983c7ec54c18ecdbb6e349 and below 399da820ecfe6f4f10c143e5c453d3559a04db9c is affected.
- Version 916f676f8dc016103f983c7ec54c18ecdbb6e349 and below f9e9cc320854a76a39e7bc92d144554f3a727fad is affected.
- Version 916f676f8dc016103f983c7ec54c18ecdbb6e349 and below 7dcf59422a3b0d20ddda844f856b4a1e0608a326 is affected.
- Version 916f676f8dc016103f983c7ec54c18ecdbb6e349 and below a4b0bf6a40f3c107c67a24fbc614510ef5719980 is affected.
- Version 3.0 is affected.
- Before 3.0 is unaffected.
- Version 2.6.39.2, <= 2.6.* 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 6.19.7, <= 6.19.* is unaffected.
- Version 7.0-rc3, <= * is unaffected.