CVE-2022-49783 (GCVE-0-2022-49783)

Vulnerability from cvelistv5 – Published: 2025-05-01 14:09 – Updated: 2025-05-04 08:45
VLAI?
Title
x86/fpu: Drop fpregs lock before inheriting FPU permissions
Summary
In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Drop fpregs lock before inheriting FPU permissions Mike Galbraith reported the following against an old fork of preempt-rt but the same issue also applies to the current preempt-rt tree. BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd preempt_count: 1, expected: 0 RCU nest depth: 0, expected: 0 Preemption disabled at: fpu_clone CPU: 6 PID: 1 Comm: systemd Tainted: G E (unreleased) Call Trace: <TASK> dump_stack_lvl ? fpu_clone __might_resched rt_spin_lock fpu_clone ? copy_thread ? copy_process ? shmem_alloc_inode ? kmem_cache_alloc ? kernel_clone ? __do_sys_clone ? do_syscall_64 ? __x64_sys_rt_sigprocmask ? syscall_exit_to_user_mode ? do_syscall_64 ? syscall_exit_to_user_mode ? do_syscall_64 ? syscall_exit_to_user_mode ? do_syscall_64 ? exc_page_fault ? entry_SYSCALL_64_after_hwframe </TASK> Mike says: The splat comes from fpu_inherit_perms() being called under fpregs_lock(), and us reaching the spin_lock_irq() therein due to fpu_state_size_dynamic() returning true despite static key __fpu_state_size_dynamic having never been enabled. Mike's assessment looks correct. fpregs_lock on a PREEMPT_RT kernel disables preemption so calling spin_lock_irq() in fpu_inherit_perms() is unsafe. This problem exists since commit 9e798e9aa14c ("x86/fpu: Prepare fpu_clone() for dynamically enabled features"). Even though the original bug report should not have enabled the paths at all, the bug still exists. fpregs_lock is necessary when editing the FPU registers or a task's FP state but it is not necessary for fpu_inherit_perms(). The only write of any FP state in fpu_inherit_perms() is for the new child which is not running yet and cannot context switch or be borrowed by a kernel thread yet. Hence, fpregs_lock is not protecting anything in the new child until clone() completes and can be dropped earlier. The siglock still needs to be acquired by fpu_inherit_perms() as the read of the parent's permissions has to be serialised. [ bp: Cleanup splat. ]
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 9e798e9aa14c45fb94e47b30bf6347b369ce9df7 , < c6e8a7a1780af3da65e78a615f7d0874da6aabb0 (git)
Affected: 9e798e9aa14c45fb94e47b30bf6347b369ce9df7 , < 36b038791e1e2baea892e9276588815fd14894b4 (git)
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    Linux Linux Affected: 5.16
Unaffected: 0 , < 5.16 (semver)
Unaffected: 6.0.10 , ≤ 6.0.* (semver)
Unaffected: 6.1 , ≤ * (original_commit_for_fix)
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "arch/x86/kernel/fpu/core.c"
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          "value": "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\u0027s 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\u0027s 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\u0027s permissions has to be serialised.\n\n  [ bp: Cleanup splat. ]"
        }
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      "providerMetadata": {
        "dateUpdated": "2025-05-04T08:45:16.690Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/c6e8a7a1780af3da65e78a615f7d0874da6aabb0"
        },
        {
          "url": "https://git.kernel.org/stable/c/36b038791e1e2baea892e9276588815fd14894b4"
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      ],
      "title": "x86/fpu: Drop fpregs lock before inheriting FPU permissions",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2022-49783",
    "datePublished": "2025-05-01T14:09:17.054Z",
    "dateReserved": "2025-05-01T14:05:17.223Z",
    "dateUpdated": "2025-05-04T08:45:16.690Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1"
}


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