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

Vulnerability from cvelistv5 – Published: 2025-05-01 14:09 – Updated: 2026-05-11 19:06
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
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7033 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
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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Show details on NVD website
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            "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: x86/fpu: Eliminar el bloqueo de fpregs antes de heredar los permisos de FPU Mike Galbraith inform\u00f3 lo siguiente contra una antigua bifurcaci\u00f3n de preempt-rt, pero el mismo problema tambi\u00e9n se aplica al \u00e1rbol preempt-rt actual. ERROR: funci\u00f3n inactiva llamada desde un contexto no v\u00e1lido en kernel/locking/spinlock_rt.c:46 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1, name: systemd preempt_count: 1, expected: 0 Profundidad de anidamiento de RCU: 0, expected: 0 Preempci\u00f3n deshabilitada en: fpu_clone CPU: 6 PID: 1 Comm: systemd Tainted: GE (no publicado) Rastreo de llamadas:   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   Mike dice: El problema se debe a que fpu_inherit_perms() se llama bajo fpregs_lock() y a que alcanzamos spin_lock_irq() debido a que fpu_state_size_dynamic() devuelve verdadero a pesar de que la clave est\u00e1tica __fpu_state_size_dynamic nunca se ha habilitado. La evaluaci\u00f3n de Mike parece correcta. fpregs_lock en un kernel PREEMPT_RT deshabilita la preempci\u00f3n, por lo que llamar a spin_lock_irq() en fpu_inherit_perms() no es seguro. Este problema existe desde la confirmaci\u00f3n 9e798e9aa14c (\"x86/fpu: Preparar fpu_clone() para funciones habilitadas din\u00e1micamente\"). Aunque el informe de error original no deber\u00eda haber habilitado las rutas, el error persiste. fpregs_lock es necesario al editar los registros de FPU o el estado de FP de una tarea, pero no es necesario para fpu_inherit_perms(). La \u00fanica escritura de cualquier estado de FP en fpu_inherit_perms() es para el nuevo hijo, que a\u00fan no se est\u00e1 ejecutando y a\u00fan no puede cambiar de contexto ni ser tomado prestado por un hilo del kernel. Por lo tanto, fpregs_lock no protege nada en el nuevo hijo hasta que clone() se complete y pueda eliminarse antes. El siglock a\u00fan debe ser adquirido por fpu_inherit_perms(), ya que la lectura de los permisos del padre debe serializarse. [bp: Limpieza splat.]"
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        "id": "CVE-2022-49783",
        "lastModified": "2026-06-17T05:19:08.250",
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                "confidentialityImpact": "NONE",
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      "cve": "CVE-2022-49783",
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: x86/fpu: Drop fpregs lock before inheriting FPU permissions",
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      "cve": "CVE-2022-49783",
      "id": "CVE-2022-49783",
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      "status": "interim",
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      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2025/cve-2022-49783.json",
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}



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