x86/cfi: Fix FineIBT hash offset in cfi_get_func_hash()

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-97944
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-25 11:17:21 UTC
Updated2026-09-25 11:17:21 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: x86/cfi: Fix FineIBT hash offset in cfi_get_func_hash() The switch of the FineIBT preamble from "subl $hash, %r10d" to the shorter "subl $hash, %eax" moved the hash immediate from offset 7 to offset 5 of the preamble. fineibt_preamble_hash was updated to match, but the open-coded offset in cfi_get_func_hash() was missed and it still reads the hash at offset 7. cfi_get_func_hash() is used by the BPF JIT to give a struct_ops trampoline the CFI hash of the stub function it stands in for. With FineIBT the trampoline now gets the upper half of the real hash followed by the first two bytes of the next instruction, so the first indirect call from the kernel into a struct_ops program, tcp_init_congestion_control() calling ->init() of a BPF congestion control for example, fails the FineIBT check and the kernel dies with a CFI failure. Move the FineIBT preamble template and its offset defines above cfi_get_func_hash() and use fineibt_preamble_hash there, so every reader of the preamble shares one definition of its layout. The CFI_FINEIBT arm is only built with CONFIG_FINEIBT, the only configuration in which cfi_mode can take that value. cfi_get_func_arity() does not need the same treatment: the __bhi_args call whose displacement it reads still ends at the function address.

Risk And Classification

EPSS: 0.001660000 probability, percentile 0.051950000 (date 2026-09-27)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 85a2d4a890dce3cfc9c14aa91afc3dd7af8e3bf5 cd9b4595d6283f9b8a35d7ae607508de45a351ce git Not specified
CNA Linux Linux affected 85a2d4a890dce3cfc9c14aa91afc3dd7af8e3bf5 67cf94c30a8b5ebc839f282f5c5a522b35903524 git Not specified
CNA Linux Linux affected 85a2d4a890dce3cfc9c14aa91afc3dd7af8e3bf5 5a5d26f2cfe13467166219f6bf58099326912ddb git Not specified
CNA Linux Linux affected 6.18 Not specified
CNA Linux Linux unaffected 6.18 semver Not specified
CNA Linux Linux unaffected 6.18.53 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.7 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc4 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/5a5d26f2cfe13467166219f6bf58099326912ddb 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/cd9b4595d6283f9b8a35d7ae607508de45a351ce 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/67cf94c30a8b5ebc839f282f5c5a522b35903524 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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