CVE-2021-46997

CVE-2021-46997 is a medium-severity vulnerability in Linux Linux Kernel with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low.

Key facts

Description

In the Linux kernel, the following vulnerability has been resolved: arm64: entry: always set GIC_PRIO_PSR_I_SET during entry Zenghui reports that booting a kernel with "irqchip.gicv3_pseudo_nmi=1" on the command line hits a warning during kernel entry, due to the way we manipulate the PMR. Early in the entry sequence, we call lockdep_hardirqs_off() to inform lockdep that interrupts have been masked (as the HW sets DAIF wqhen entering an exception). Architecturally PMR_EL1 is not affected by exception entry, and we don't set GIC_PRIO_PSR_I_SET in the PMR early in the exception entry sequence, so early in exception entry the PMR can indicate that interrupts are unmasked even though they are masked by DAIF. If DEBUG_LOCKDEP is selected, lockdep_hardirqs_off() will check that interrupts are masked, before we set GIC_PRIO_PSR_I_SET in any of the exception entry paths, and hence lockdep_hardirqs_off() will WARN() that something is amiss. We can avoid this by consistently setting GIC_PRIO_PSR_I_SET during exception entry so that kernel code sees a consistent environment. We must also update local_daif_inherit() to undo this, as currently only touches DAIF. For other paths, local_daif_restore() will update both DAIF and the PMR. With this done, we can remove the existing special cases which set this later in the entry code. We always use (GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET) for consistency with local_daif_save(), as this will warn if it ever encounters (GIC_PRIO_IRQOFF | GIC_PRIO_PSR_I_SET), and never sets this itself. This matches the gic_prio_kentry_setup that we have to retain for ret_to_user. The original splat from Zenghui's report was: | DEBUG_LOCKS_WARN_ON(!irqs_disabled()) | WARNING: CPU: 3 PID: 125 at kernel/locking/lockdep.c:4258 lockdep_hardirqs_off+0xd4/0xe8 | Modules linked in: | CPU: 3 PID: 125 Comm: modprobe Tainted: G W 5.12.0-rc8+ #463 | Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 | pstate: 604003c5 (nZCv DAIF +PAN -UAO -TCO BTYPE=--) | pc : lockdep_hardirqs_off+0xd4/0xe8 | lr : lockdep_hardirqs_off+0xd4/0xe8 | sp : ffff80002a39bad0 | pmr_save: 000000e0 | x29: ffff80002a39bad0 x28: ffff0000de214bc0 | x27: ffff0000de1c0400 x26: 000000000049b328 | x25: 0000000000406f30 x24: ffff0000de1c00a0 | x23: 0000000020400005 x22: ffff8000105f747c | x21: 0000000096000044 x20: 0000000000498ef9 | x19: ffff80002a39bc88 x18: ffffffffffffffff | x17: 0000000000000000 x16: ffff800011c61eb0 | x15: ffff800011700a88 x14: 0720072007200720 | x13: 0720072007200720 x12: 0720072007200720 | x11: 0720072007200720 x10: 0720072007200720 | x9 : ffff80002a39bad0 x8 : ffff80002a39bad0 | x7 : ffff8000119f0800 x6 : c0000000ffff7fff | x5 : ffff8000119f07a8 x4 : 0000000000000001 | x3 : 9bcdab23f2432800 x2 : ffff800011730538 | x1 : 9bcdab23f2432800 x0 : 0000000000000000 | Call trace: | lockdep_hardirqs_off+0xd4/0xe8 | enter_from_kernel_mode.isra.5+0x7c/0xa8 | el1_abort+0x24/0x100 | el1_sync_handler+0x80/0xd0 | el1_sync+0x6c/0x100 | __arch_clear_user+0xc/0x90 | load_elf_binary+0x9fc/0x1450 | bprm_execve+0x404/0x880 | kernel_execve+0x180/0x188 | call_usermodehelper_exec_async+0xdc/0x158 | ret_from_fork+0x10/0x18

Frequently asked questions

What is CVE-2021-46997?
In the Linux kernel, the following vulnerability has been resolved: arm64: entry: always set GIC_PRIO_PSR_I_SET during entry Zenghui reports that booting a kernel with "irqchip.gicv3_pseudo_nmi=1" on the command line hits a warning during kernel entry, due to the way we manipulate the PMR. Early in the entry sequence, we call lockdep_hardirqs_off() to inform lockdep that interrupts have been masked (as the HW sets DAIF wqhen entering an exception). Architecturally PMR_EL1 is not affected by exception entry, and we don't set GIC_PRIO_PSR_I_SET in the PMR early in the exception entry sequence, so early in exception entry the PMR can indicate that interrupts are unmasked even though they are masked by DAIF. If DEBUG_LOCKDEP is selected, lockdep_hardirqs_off() will check that interrupts are masked, before we set GIC_PRIO_PSR_I_SET in any of the exception entry paths, and hence lockdep_hardirqs_off() will WARN() that something is amiss. We can avoid this by consistently setting GIC_PRIO_PSR_I_SET during exception entry so that kernel code sees a consistent environment. We must also update local_daif_inherit() to undo this, as currently only touches DAIF. For other paths, local_daif_restore() will update both DAIF and the PMR. With this done, we can remove the existing special cases which set this later in the entry code. We always use (GIC_PRIO_IRQON | GIC_PRIO_PSR_I_SET) for consistency with local_daif_save(), as this will warn if it ever encounters (GIC_PRIO_IRQOFF | GIC_PRIO_PSR_I_SET), and never sets this itself. This matches the gic_prio_kentry_setup that we have to retain for ret_to_user. The original splat from Zenghui's report was: | DEBUG_LOCKS_WARN_ON(!irqs_disabled()) | WARNING: CPU: 3 PID: 125 at kernel/locking/lockdep.c:4258 lockdep_hardirqs_off+0xd4/0xe8 | Modules linked in: | CPU: 3 PID: 125 Comm: modprobe Tainted: G W 5.12.0-rc8+ #463 | Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015 | pstate: 604003c5 (nZCv DAIF +PAN -UAO -TCO BTYPE=--) | pc : lockdep_hardirqs_off+0xd4/0xe8 | lr : lockdep_hardirqs_off+0xd4/0xe8 | sp : ffff80002a39bad0 | pmr_save: 000000e0 | x29: ffff80002a39bad0 x28: ffff0000de214bc0 | x27: ffff0000de1c0400 x26: 000000000049b328 | x25: 0000000000406f30 x24: ffff0000de1c00a0 | x23: 0000000020400005 x22: ffff8000105f747c | x21: 0000000096000044 x20: 0000000000498ef9 | x19: ffff80002a39bc88 x18: ffffffffffffffff | x17: 0000000000000000 x16: ffff800011c61eb0 | x15: ffff800011700a88 x14: 0720072007200720 | x13: 0720072007200720 x12: 0720072007200720 | x11: 0720072007200720 x10: 0720072007200720 | x9 : ffff80002a39bad0 x8 : ffff80002a39bad0 | x7 : ffff8000119f0800 x6 : c0000000ffff7fff | x5 : ffff8000119f07a8 x4 : 0000000000000001 | x3 : 9bcdab23f2432800 x2 : ffff800011730538 | x1 : 9bcdab23f2432800 x0 : 0000000000000000 | Call trace: | lockdep_hardirqs_off+0xd4/0xe8 | enter_from_kernel_mode.isra.5+0x7c/0xa8 | el1_abort+0x24/0x100 | el1_sync_handler+0x80/0xd0 | el1_sync+0x6c/0x100 | __arch_clear_user+0xc/0x90 | load_elf_binary+0x9fc/0x1450 | bprm_execve+0x404/0x880 | kernel_execve+0x180/0x188 | call_usermodehelper_exec_async+0xdc/0x158 | ret_from_fork+0x10/0x18
How severe is CVE-2021-46997?
CVE-2021-46997 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-46997 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (16th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-46997?
CVE-2021-46997 affects Linux Linux Kernel. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-46997?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2021-46997 have an EU (EUVD) identifier?
Yes. CVE-2021-46997 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-33645.
When was CVE-2021-46997 published?
CVE-2021-46997 was published on 2024-02-28 and last updated on 2026-06-17.

References

Affected products (1)

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