Description
In 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.
Published: 2026-09-25
Score: n/a
EPSS: n/a
KEV: No
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History

Fri, 25 Sep 2026 15:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-665

Fri, 25 Sep 2026 10:30:00 +0000

Type Values Removed Values Added
Description In 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.
Title x86/cfi: Fix FineIBT hash offset in cfi_get_func_hash()
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

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Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-09-25T10:22:55.382Z

Reserved: 2026-09-25T10:18:58.204Z

Link: CVE-2026-97944

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-25T11:17:21.870

Modified: 2026-09-25T11:17:21.870

Link: CVE-2026-97944

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-25T15:00:20Z

Weaknesses