From ea0d55ae4b3207c33691a73da3443b1fd379f1d2 Mon Sep 17 00:00:00 2001 From: Ada Couprie Diaz Date: Tue, 14 Oct 2025 10:25:36 +0100 Subject: [PATCH] arm64: debug: always unmask interrupts in el0_softstp() 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: 0ac7584c08ce ("arm64: debug: split single stepping exception entry") Cc: # 6.17 Signed-off-by: Ada Couprie Diaz Acked-by: Mark Rutland [catalin.marinas@arm.com: added Mark's rewritten commit log and some whitespace] Signed-off-by: Catalin Marinas --- arch/arm64/kernel/entry-common.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c index f546a914f041..a9c81715ce59 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -697,6 +697,8 @@ static void noinstr el0_breakpt(struct pt_regs *regs, unsigned long esr) static void noinstr el0_softstp(struct pt_regs *regs, unsigned long esr) { + bool step_done; + if (!is_ttbr0_addr(regs->pc)) arm64_apply_bp_hardening(); @@ -707,10 +709,10 @@ static void noinstr el0_softstp(struct pt_regs *regs, unsigned long esr) * If we are stepping a suspended breakpoint there's nothing more to do: * the single-step is complete. */ - if (!try_step_suspended_breakpoints(regs)) { - local_daif_restore(DAIF_PROCCTX); + step_done = try_step_suspended_breakpoints(regs); + local_daif_restore(DAIF_PROCCTX); + if (!step_done) do_el0_softstep(esr, regs); - } arm64_exit_to_user_mode(regs); } -- 2.47.3