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arm64: debug: always unmask interrupts in el0_softstp()

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commit ea0d55ae4b upstream.

We intend that EL0 exception handlers unmask all DAIF exceptions
before calling exit_to_user_mode().

When completing single-step of a suspended breakpoint, we do not call
local_daif_restore(DAIF_PROCCTX) before calling exit_to_user_mode(),
leaving all DAIF exceptions masked.

When pseudo-NMIs are not in use this is benign.

When pseudo-NMIs are in use, this is unsound. At this point interrupts
are masked by both DAIF.IF and PMR_EL1, and subsequent irq flag
manipulation may not work correctly. For example, a subsequent
local_irq_enable() within exit_to_user_mode_loop() will only unmask
interrupts via PMR_EL1 (leaving those masked via DAIF.IF), and
anything depending on interrupts being unmasked (e.g. delivery of
signals) will not work correctly.

This was detected by CONFIG_ARM64_DEBUG_PRIORITY_MASKING.

Move the call to `try_step_suspended_breakpoints()` outside of the check
so that interrupts can be unmasked even if we don't call the step handler.

Fixes: 0ac7584c08 ("arm64: debug: split single stepping exception entry")
Cc: <stable@vger.kernel.org> # 6.17
Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
[catalin.marinas@arm.com: added Mark's rewritten commit log and some whitespace]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
[ada.coupriediaz@arm.com: Fix conflict for v6.17 stable]
Signed-off-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ada Couprie Diaz 2025-10-14 10:25:36 +01:00 • committed by Greg Kroah-Hartman
commit fb84a10125
1 changed files with 5 additions and 3 deletions
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