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arm64: hibernate: mask DAIF before restoring hibernated kernel

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The arm64 hibernate code manages the exception masking in an unsound
way, leading to potential crashes and/or warnings during resume.

When a hibernation image is saved in `swsusp_arch_suspend()`, all DAIF
exceptions are masked (by virtue of `local_daif_save()`), and the
suspended image is saved assuming that all DAIF exceptions will remain
masked when the image is restored.

When a hibernation image is resumed by `swsusp_arch_resume()`, only
interrupts are masked (by virtue of `local_irq_disable()` in
`resume_target_kernel()`). When pseudo-NMI is enabled the DAIF.IF bits
will be clear, and regardless of pseudo-NMI the DAIF.DA bits will be
clear.

This means that there are two problems:

(1) It is possible to take Debug, SError, or pseudo-NMI exceptions
    during the resume process. This is unsafe, as during the resume
    process both the old ane new kernels will tranisently be in an
    inconsistent state, and swsusp_arch_suspend_exit() won't retain
    an executable mapping of any exception vectors.

    Any exception taken here will be fatal and silent.

(2) When re-entering the resumed kernel, some DAIF bits will be clear
    unexpectedly. This permits Debug, SError, or pseudo-NMI exceptions
    to be taken for a short period while the resumed kernel is not yet
    in a consistent state.

    This is detected by CONFIG_ARM64_DEBUG_PRIORITY_MASKING.

Avoid these issues by masking all DAIF exceptions during resume.

Fixes: 82869ac57b ("arm64: kernel: Add support for hibernate/suspend-to-disk")
Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Ada Couprie Diaz 2026-07-27 17:34:11 +01:00 committed by Will Deacon
parent 7cf2d6efb8
commit 684bde1001
1 changed files with 12 additions and 0 deletions
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12
arch/arm64/kernel/hibernate.c
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@ -465,9 +465,21 @@ int __nocfi swsusp_arch_resume(void)
if (el2_reset_needed())
__hyp_set_vectors(el2_vectors);
/*
* It is necessary to mask all DAIF exceptions here as:
*
* - The copy of swsusp_arch_suspend_exit() in the hibernation
* text cannot handle taking any exceptions.
*
* - The suspended kernel masked all DAIF exceptions in
* swsusp_arch_resume(), and expects to be re-entered in the
* same state : with all DAIF exceptions masked.
*/
local_daif_save();
hibernate_exit(virt_to_phys(tmp_pg_dir), resume_hdr.ttbr1_el1,
resume_hdr.reenter_kernel, restore_pblist,
resume_hdr.__hyp_stub_vectors, virt_to_phys(zero_page));
unreachable();
return 0;
}