{"api_version":"1","generated_at":"2026-11-11T07:03:11+00:00","cve":"CVE-2025-38170","urls":{"html":"https://cve.report/CVE-2025-38170","api":"https://cve.report/api/cve/CVE-2025-38170.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2025-38170","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2025-38170"},"summary":{"title":"arm64/fpsimd: Discard stale CPU state when handling SME traps","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 ]","state":"PUBLISHED","assigner":"Linux","published_at":"2025-07-03 09:15:32","updated_at":"2026-11-05 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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 ]"}],"providerMetadata":{"dateUpdated":"2026-05-11T21:22:36.924Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/de89368de3894a8db27caeb8fd902ba1c49f696a"},{"url":"https://git.kernel.org/stable/c/43be952e885476dafb74aa832c0847b2f4f650c6"},{"url":"https://git.kernel.org/stable/c/6103f9ba51a59afb5a0f32299c837377c5a5a693"},{"url":"https://git.kernel.org/stable/c/c4a4786d93e99517d6f10ed56b9ffba4ce88d3b3"},{"url":"https://git.kernel.org/stable/c/d3eaab3c70905c5467e5c4ea403053d67505adeb"}],"title":"arm64/fpsimd: Discard stale CPU state when handling SME traps","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2025-38170","datePublished":"2025-07-03T08:36:09.012Z","dateReserved":"2025-04-16T04:51:23.991Z","dateUpdated":"2026-11-05T20:52:18.397Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2025-07-03 09:15:32","lastModifiedDate":"2026-11-05 21:18:12","problem_types":["NVD-CWE-noinfo"],"metrics":{"cvssMetricV31":[{"source":"nvd@nist.gov","type":"Primary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","baseScore":5.5,"baseSeverity":"MEDIUM","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":3.6}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-11-05T20:50:47.797468Z","id":"CVE-2025-38170","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.19","versionEndExcluding":"6.1.142","matchCriteriaId":"8AC7C3FA-F2C7-4A80-A5BB-45E85C1E2C78"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.2","versionEndExcluding":"6.6.94","matchCriteriaId":"304E3F01-7D7A-4908-994E-7F95C5C00B06"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.7","versionEndExcluding":"6.12.34","matchCriteriaId":"4FFA54AA-CDFE-4591-BD07-72813D0948F4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.13","versionEndExcluding":"6.15.3","matchCriteriaId":"0541C761-BD5E-4C1A-8432-83B375D7EB92"}]}]},{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*","matchCriteriaId":"FA6FEEC2-9F11-4643-8827-749718254FED"}]}]}]},"legacy_mitre":{"record":{"CveYear":"2025","CveId":"38170","Ordinal":"1","Title":"arm64/fpsimd: Discard stale CPU state when handling SME traps","CVE":"CVE-2025-38170","Year":"2025"},"notes":[{"CveYear":"2025","CveId":"38170","Ordinal":"1","NoteData":"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 ]","Type":"Description","Title":"arm64/fpsimd: Discard stale CPU state when handling SME traps"}]}}}