arm64/fpsimd: Discard stale CPU state when handling SME traps

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-38170
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-07-03 09:15:32 UTC
Updated2026-11-05 21:18:12 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: arm64/fpsimd: Discard stale CPU state when handling SME traps The logic for handling SME traps manipulates saved FPSIMD/SVE/SME state incorrectly, and a race with preemption can result in a task having TIF_SME set and TIF_FOREIGN_FPSTATE clear even though the live CPU state is stale (e.g. with SME traps enabled). This can result in warnings from do_sme_acc() where SME traps are not expected while TIF_SME is set: | /* With TIF_SME userspace shouldn't generate any traps */ | if (test_and_set_thread_flag(TIF_SME)) | WARN_ON(1); This is very similar to the SVE issue we fixed in commit: 751ecf6afd6568ad ("arm64/sve: Discard stale CPU state when handling SVE traps") The race can occur when the SME trap handler is preempted before and after manipulating the saved FPSIMD/SVE/SME state, starting and ending on the same CPU, e.g. | void do_sme_acc(unsigned long esr, struct pt_regs *regs) | { | // Trap on CPU 0 with TIF_SME clear, SME traps enabled | // task->fpsimd_cpu is 0. | // per_cpu_ptr(&fpsimd_last_state, 0) is task. | | ... | | // Preempted; migrated from CPU 0 to CPU 1. | // TIF_FOREIGN_FPSTATE is set. | | get_cpu_fpsimd_context(); | | /* With TIF_SME userspace shouldn't generate any traps */ | if (test_and_set_thread_flag(TIF_SME)) | WARN_ON(1); | | if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) { | unsigned long vq_minus_one = | sve_vq_from_vl(task_get_sme_vl(current)) - 1; | sme_set_vq(vq_minus_one); | | fpsimd_bind_task_to_cpu(); | } | | put_cpu_fpsimd_context(); | | // Preempted; migrated from CPU 1 to CPU 0. | // task->fpsimd_cpu is still 0 | // If per_cpu_ptr(&fpsimd_last_state, 0) is still task then: | // - Stale HW state is reused (with SME traps enabled) | // - TIF_FOREIGN_FPSTATE is cleared | // - A return to userspace skips HW state restore | } Fix the case where the state is not live and TIF_FOREIGN_FPSTATE is set by calling fpsimd_flush_task_state() to detach from the saved CPU state. This ensures that a subsequent context switch will not reuse the stale CPU state, and will instead set TIF_FOREIGN_FPSTATE, forcing the new state to be reloaded from memory prior to a return to userspace. Note: this was originallly posted as [1]. [ Rutland: rewrite commit message ]

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: NVD-CWE-noinfo

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 8bd7f91c03d886f41d35f6108078d20be5a4a1bd de89368de3894a8db27caeb8fd902ba1c49f696a git Not specified
CNA Linux Linux affected 8bd7f91c03d886f41d35f6108078d20be5a4a1bd 43be952e885476dafb74aa832c0847b2f4f650c6 git Not specified
CNA Linux Linux affected 8bd7f91c03d886f41d35f6108078d20be5a4a1bd 6103f9ba51a59afb5a0f32299c837377c5a5a693 git Not specified
CNA Linux Linux affected 8bd7f91c03d886f41d35f6108078d20be5a4a1bd c4a4786d93e99517d6f10ed56b9ffba4ce88d3b3 git Not specified
CNA Linux Linux affected 8bd7f91c03d886f41d35f6108078d20be5a4a1bd d3eaab3c70905c5467e5c4ea403053d67505adeb git Not specified
CNA Linux Linux affected 5.19 Not specified
CNA Linux Linux unaffected 5.19 semver Not specified
CNA Linux Linux unaffected 6.1.142 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.94 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.34 6.12.* semver Not specified
CNA Linux Linux unaffected 6.15.3 6.15.* semver Not specified
CNA Linux Linux unaffected 6.16 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
lists.debian.org/debian-lts-announce/2025/10/msg00008.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Third Party Advisory
git.kernel.org/stable/c/43be952e885476dafb74aa832c0847b2f4f650c6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/d3eaab3c70905c5467e5c4ea403053d67505adeb 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/c4a4786d93e99517d6f10ed56b9ffba4ce88d3b3 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/de89368de3894a8db27caeb8fd902ba1c49f696a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/6103f9ba51a59afb5a0f32299c837377c5a5a693 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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