UBUNTU-CVE-2025-38170
In 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 ]
02 / AFFECTED SOFTWARE
Affected packages
50 explicit affected versions
6 explicit affected versions
11 explicit affected versions
12 explicit affected versions
19 explicit affected versions
6 explicit affected versions
24 explicit affected versions
10 explicit affected versions
28 explicit affected versions
26 explicit affected versions
7 explicit affected versions
32 explicit affected versions
13 explicit affected versions
35 explicit affected versions
35 explicit affected versions
18 explicit affected versions
37 explicit affected versions
13 explicit affected versions
4 explicit affected versions
23 explicit affected versions
43 explicit affected versions
1 explicit affected versions
21 explicit affected versions
9 explicit affected versions
16 explicit affected versions
10 explicit affected versions
39 explicit affected versions
8 explicit affected versions
7 explicit affected versions
12 explicit affected versions
5 explicit affected versions
7 explicit affected versions
12 explicit affected versions
14 explicit affected versions
10 explicit affected versions
1 explicit affected versions
7 explicit affected versions
9 explicit affected versions
12 explicit affected versions
12 explicit affected versions
32 explicit affected versions
7 explicit affected versions
23 explicit affected versions
25 explicit affected versions
10 explicit affected versions
37 explicit affected versions
10 explicit affected versions
13 explicit affected versions
31 explicit affected versions
2 explicit affected versions
10 explicit affected versions
5 explicit affected versions
26 explicit affected versions
3 explicit affected versions
13 explicit affected versions
29 explicit affected versions
13 explicit affected versions
6 explicit affected versions
32 explicit affected versions
32 explicit affected versions
33 explicit affected versions
23 explicit affected versions
10 explicit affected versions
11 explicit affected versions
10 explicit affected versions
11 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
10 explicit affected versions
26 explicit affected versions
31 explicit affected versions
26 explicit affected versions
38 explicit affected versions
5 explicit affected versions
13 explicit affected versions
37 explicit affected versions
16 explicit affected versions
41 explicit affected versions
3 explicit affected versions
7 explicit affected versions
51 explicit affected versions
18 explicit affected versions
33 explicit affected versions
12 explicit affected versions
27 explicit affected versions
34 explicit affected versions
8 explicit affected versions
5 explicit affected versions
3 explicit affected versions
8 explicit affected versions
10 explicit affected versions
7 explicit affected versions
37 explicit affected versions
13 explicit affected versions
13 explicit affected versions
7 explicit affected versions
8 explicit affected versions
10 explicit affected versions
12 explicit affected versions
3 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
42 explicit affected versions
14 explicit affected versions
38 explicit affected versions
9 explicit affected versions
11 explicit affected versions
30 explicit affected versions
13 explicit affected versions
8 explicit affected versions
7 explicit affected versions
4 explicit affected versions
1 explicit affected versions
13 explicit affected versions
43 explicit affected versions
10 explicit affected versions
8 explicit affected versions
36 explicit affected versions
14 explicit affected versions
4 explicit affected versions
78 explicit affected versions
11 explicit affected versions
1 explicit affected versions
10 explicit affected versions
30 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In 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 ]
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/d3eaab3c70905c5467e5c4ea403053d67505adeb
- https://git.kernel.org/stable/c/43be952e885476dafb74aa832c0847b2f4f650c6
- https://git.kernel.org/stable/c/6103f9ba51a59afb5a0f32299c837377c5a5a693
- https://git.kernel.org/stable/c/c4a4786d93e99517d6f10ed56b9ffba4ce88d3b3
- https://git.kernel.org/stable/c/d3eaab3c70905c5467e5c4ea403053d67505adeb
- https://git.kernel.org/stable/c/de89368de3894a8db27caeb8fd902ba1c49f696a
- https://ubuntu.com/security/CVE-2025-38170
- https://ubuntu.com/security/notices/USN-7769-1
- https://ubuntu.com/security/notices/USN-7769-2
- https://ubuntu.com/security/notices/USN-7769-3
- https://ubuntu.com/security/notices/USN-7770-1
- https://ubuntu.com/security/notices/USN-7771-1
- https://ubuntu.com/security/notices/USN-7789-1
- https://ubuntu.com/security/notices/USN-7789-2
- https://ubuntu.com/security/notices/USN-8028-1
- https://ubuntu.com/security/notices/USN-8028-2
- https://ubuntu.com/security/notices/USN-8028-3
- https://ubuntu.com/security/notices/USN-8028-4
- https://ubuntu.com/security/notices/USN-8028-5
- https://ubuntu.com/security/notices/USN-8028-6
- https://ubuntu.com/security/notices/USN-8028-7
- https://ubuntu.com/security/notices/USN-8028-8
- https://ubuntu.com/security/notices/USN-8031-1
- https://ubuntu.com/security/notices/USN-8031-2
- https://ubuntu.com/security/notices/USN-8031-3
- https://ubuntu.com/security/notices/USN-8052-1
- https://ubuntu.com/security/notices/USN-8052-2
- https://ubuntu.com/security/notices/USN-8074-1
- https://ubuntu.com/security/notices/USN-8074-2
- https://ubuntu.com/security/notices/USN-8126-1
- https://www.cve.org/CVERecord?id=CVE-2025-38170