{"id":"CVE-2022-49783","summary":"x86/fpu: Drop fpregs lock before inheriting FPU permissions","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nx86/fpu: Drop fpregs lock before inheriting FPU permissions\n\nMike Galbraith reported the following against an old fork of preempt-rt\nbut the same issue also applies to the current preempt-rt tree.\n\n   BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46\n   in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd\n   preempt_count: 1, expected: 0\n   RCU nest depth: 0, expected: 0\n   Preemption disabled at:\n   fpu_clone\n   CPU: 6 PID: 1 Comm: systemd Tainted: G            E       (unreleased)\n   Call Trace:\n    \u003cTASK\u003e\n    dump_stack_lvl\n    ? fpu_clone\n    __might_resched\n    rt_spin_lock\n    fpu_clone\n    ? copy_thread\n    ? copy_process\n    ? shmem_alloc_inode\n    ? kmem_cache_alloc\n    ? kernel_clone\n    ? __do_sys_clone\n    ? do_syscall_64\n    ? __x64_sys_rt_sigprocmask\n    ? syscall_exit_to_user_mode\n    ? do_syscall_64\n    ? syscall_exit_to_user_mode\n    ? do_syscall_64\n    ? syscall_exit_to_user_mode\n    ? do_syscall_64\n    ? exc_page_fault\n    ? entry_SYSCALL_64_after_hwframe\n    \u003c/TASK\u003e\n\nMike says:\n\n  The splat comes from fpu_inherit_perms() being called under fpregs_lock(),\n  and us reaching the spin_lock_irq() therein due to fpu_state_size_dynamic()\n  returning true despite static key __fpu_state_size_dynamic having never\n  been enabled.\n\nMike's assessment looks correct. fpregs_lock on a PREEMPT_RT kernel disables\npreemption so calling spin_lock_irq() in fpu_inherit_perms() is unsafe. This\nproblem exists since commit\n\n  9e798e9aa14c (\"x86/fpu: Prepare fpu_clone() for dynamically enabled features\").\n\nEven though the original bug report should not have enabled the paths at\nall, the bug still exists.\n\nfpregs_lock is necessary when editing the FPU registers or a task's FP\nstate but it is not necessary for fpu_inherit_perms(). The only write\nof any FP state in fpu_inherit_perms() is for the new child which is\nnot running yet and cannot context switch or be borrowed by a kernel\nthread yet. Hence, fpregs_lock is not protecting anything in the new\nchild until clone() completes and can be dropped earlier. The siglock\nstill needs to be acquired by fpu_inherit_perms() as the read of the\nparent's permissions has to be serialised.\n\n  [ bp: Cleanup splat. ]","modified":"2026-04-03T13:14:27.837678Z","published":"2025-05-01T14:09:17.054Z","related":["SUSE-SU-2025:01918-1","SUSE-SU-2025:01966-1","SUSE-SU-2025:02173-1","SUSE-SU-2025:02262-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2022/49xxx/CVE-2022-49783.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/36b038791e1e2baea892e9276588815fd14894b4"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c6e8a7a1780af3da65e78a615f7d0874da6aabb0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2022/49xxx/CVE-2022-49783.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2022-49783"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"9e798e9aa14c45fb94e47b30bf6347b369ce9df7"},{"fixed":"c6e8a7a1780af3da65e78a615f7d0874da6aabb0"},{"fixed":"36b038791e1e2baea892e9276588815fd14894b4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2022-49783.json"}}],"schema_version":"1.7.5"}