{"cve":"CVE-2025-38170","nvd":{"published":"2025-07-03T09:15:32.643","modified":"2026-06-17T09:16:18.920","status":"Analyzed","description":"In the Linux kernel, the following vulnerability has been resolved:\n\narm64/fpsimd: Discard stale CPU state when handling SME traps\n\nThe logic for handling SME traps manipulates saved FPSIMD/SVE/SME state\nincorrectly, and a race with preemption can result in a task having\nTIF_SME set and TIF_FOREIGN_FPSTATE clear even though the live CPU state\nis stale (e.g. with SME traps enabled). This can result in warnings from\ndo_sme_acc() where SME traps are not expected while TIF_SME is set:\n\n|        /* With TIF_SME userspace shouldn't generate any traps */\n|        if (test_and_set_thread_flag(TIF_SME))\n|                WARN_ON(1);\n\nThis is very similar to the SVE issue we fixed in commit:\n\n  751ecf6afd6568ad (\"arm64/sve: Discard stale CPU state when handling SVE traps\")\n\nThe race can occur when the SME trap handler is preempted before and\nafter manipulating the saved FPSIMD/SVE/SME state, starting and ending on\nthe same CPU, e.g.\n\n| void do_sme_acc(unsigned long esr, struct pt_regs *regs)\n| {\n|         // Trap on CPU 0 with TIF_SME clear, SME traps enabled\n|         // task->fpsimd_cpu is 0.\n|         // per_cpu_ptr(&fpsimd_last_state, 0) is task.\n|\n|         ...\n|\n|         // Preempted; migrated from CPU 0 to CPU 1.\n|         // TIF_FOREIGN_FPSTATE is set.\n|\n|         get_cpu_fpsimd_context();\n|\n|         /* With TIF_SME userspace shouldn't generate any traps */\n|         if (test_and_set_thread_flag(TIF_SME))\n|                 WARN_ON(1);\n|\n|         if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) {\n|                 unsigned long vq_minus_one =\n|                         sve_vq_from_vl(task_get_sme_vl(current)) - 1;\n|                 sme_set_vq(vq_minus_one);\n|\n|                 fpsimd_bind_task_to_cpu();\n|         }\n|\n|         put_cpu_fpsimd_context();\n|\n|         // Preempted; migrated from CPU 1 to CPU 0.\n|         // task->fpsimd_cpu is still 0\n|         // If per_cpu_ptr(&fpsimd_last_state, 0) is still task then:\n|         // - Stale HW state is reused (with SME traps enabled)\n|         // - TIF_FOREIGN_FPSTATE is cleared\n|         // - A return to userspace skips HW state restore\n| }\n\nFix the case where the state is not live and TIF_FOREIGN_FPSTATE is set\nby calling fpsimd_flush_task_state() to detach from the saved CPU\nstate. This ensures that a subsequent context switch will not reuse the\nstale CPU state, and will instead set TIF_FOREIGN_FPSTATE, forcing the\nnew state to be reloaded from memory prior to a return to userspace.\n\nNote: this was originallly posted as [1].\n\n[ Rutland: rewrite commit message ]","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","score":5.5},"cwes":[],"references":["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"],"products":["debian:debian_linux","linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:04:28.436527499+00:00"},"epss":{"cve":"CVE-2025-38170","score":0.00166,"percentile":0.05872,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}