{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2025-68171", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2025-12-16T13:41:40.251Z", "datePublished": "2025-12-16T13:42:51.121Z", "dateUpdated": "2026-08-05T12:09:59.980Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:09:59.980Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/fpu: Ensure XFD state on signal delivery\n\nSean reported [1] the following splat when running KVM tests:\n\n WARNING: CPU: 232 PID: 15391 at xfd_validate_state+0x65/0x70\n Call Trace:\n \n fpu__clear_user_states+0x9c/0x100\n arch_do_signal_or_restart+0x142/0x210\n exit_to_user_mode_loop+0x55/0x100\n do_syscall_64+0x205/0x2c0\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n\nChao further identified [2] a reproducible scenario involving signal\ndelivery: a non-AMX task is preempted by an AMX-enabled task which\nmodifies the XFD MSR.\n\nWhen the non-AMX task resumes and reloads XSTATE with init values,\na warning is triggered due to a mismatch between fpstate::xfd and the\nCPU's current XFD state. fpu__clear_user_states() does not currently\nre-synchronize the XFD state after such preemption.\n\nInvoke xfd_update_state() which detects and corrects the mismatch if\nthere is a dynamic feature.\n\nThis also benefits the sigreturn path, as fpu__restore_sig() may call\nfpu__clear_user_states() when the sigframe is inaccessible.\n\n[ dhansen: minor changelog munging ]" } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The vulnerable code is reached only through local task-context paths — signal delivery from `arch_do_signal_or_restart()` and the `rt_sigreturn` syscall — requiring the attacker to execute code on the machine. No network or adjacent-network reachability exists.\nAC:L - The attacker controls both sides of the race: it runs its own AMX-enabled and non-AMX threads, pins them to a chosen CPU, floods signals, and can force a scheduling point in the exact window between `copy_fpstate_to_sigframe()` and `fpu__clear_user_states()` by faulting on userfaultfd-backed sigframe pages. AMX/XFD-capable Xeons (Sapphire Rapids and later) are mainstream cloud/datacenter hardware, so the required configuration is a normal deployment rather than a rare precondition.\nPR:L - Any unprivileged local user can deliver signals to its own threads, call `arch_prctl(ARCH_REQ_XCOMP_PERM, XFEATURE_XTILEDATA)`, set CPU affinity, and invoke `rt_sigreturn` with an inaccessible sigframe — there is no capability, namespace, or LSM check anywhere on the path.\nUI:N - The attacker triggers the entire sequence from its own processes via signals and scheduling; no action by any other user is required.\nS:U - The XFD desync and its consequences stay within the kernel's own security authority on the host — there is no guest-to-host escape, IOMMU bypass, or other crossing of a security-authority boundary.\nC:H - The stale XFD causes the XRSTOR that is specifically responsible for scrubbing dynamic-feature state left by the previous task to skip XTILEDATA, and `fpregs_mark_activate()` suppresses the later corrective restore, so up to 8 KiB of another process's AMX tile register content survives into the attacker's context and can be dumped with a userspace `XSAVE` after re-enabling XFD via #NM; the debug WARN additionally discloses kernel addresses.\nI:H - The same primitive works in reverse — attacker-chosen tile register content is left un-scrubbed and becomes the operating state of a victim AMX process, silently corrupting its computation — and the desync also lets a task use AMX with no `ARCH_REQ_XCOMP_PERM` grant while its fpstate has no XTILEDATA storage, bypassing the dynamic-xstate permission model and silently discarding FPU state across context switches.\nA:H - The mismatch trips `WARN_ON_ONCE()` in `xfd_validate_state()` from both `os_xrstor()` and the subsequent `os_xsave()` (the reported splat), which is a fatal panic on systems booted with `panic_on_warn=1`, and leaves the FPU state machine persistently inconsistent with the hardware." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kernel/fpu/core.c" ], "versions": [ { "version": "672365477ae8afca5a1cca98c1deb733235e4525", "lessThan": "eefbfb722042fc9210d2e0ac2b063fd1abf51895", "status": "affected", "versionType": "git" }, { "version": "672365477ae8afca5a1cca98c1deb733235e4525", "lessThan": "1811c610653c0cd21cc9add14595b7cffaeca511", "status": "affected", "versionType": "git" }, { "version": "672365477ae8afca5a1cca98c1deb733235e4525", "lessThan": "5b2619b488f1d08b960c43c6468dd0759e8b3035", "status": "affected", "versionType": "git" }, { "version": "672365477ae8afca5a1cca98c1deb733235e4525", "lessThan": "3f735419c4b43cde42e6d408db39137b82474e31", "status": "affected", "versionType": "git" }, { "version": "672365477ae8afca5a1cca98c1deb733235e4525", "lessThan": "388eff894d6bc5f921e9bfff0e4b0ab2684a96e9", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kernel/fpu/core.c" ], "versions": [ { "version": "5.16", "status": "affected" }, { "version": "0", "lessThan": "5.16", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.159", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.117", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.58", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.17.8", "lessThanOrEqual": "6.17.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.159" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.6.117" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.12.58" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.17.8" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.18" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/eefbfb722042fc9210d2e0ac2b063fd1abf51895" }, { "url": "https://git.kernel.org/stable/c/1811c610653c0cd21cc9add14595b7cffaeca511" }, { "url": "https://git.kernel.org/stable/c/5b2619b488f1d08b960c43c6468dd0759e8b3035" }, { "url": "https://git.kernel.org/stable/c/3f735419c4b43cde42e6d408db39137b82474e31" }, { "url": "https://git.kernel.org/stable/c/388eff894d6bc5f921e9bfff0e4b0ab2684a96e9" } ], "title": "x86/fpu: Ensure XFD state on signal delivery", "x_generator": { "engine": "bippy-1.2.0" } } } }