From e9ad390a4812fd60c1da46823f7a6f84f2411f0c Mon Sep 17 00:00:00 2001 From: Lorenzo Pieralisi Date: Tue, 7 Oct 2025 12:26:00 +0200 Subject: [PATCH 1/2] arm64/sysreg: Fix GIC CDEOI instruction encoding The GIC CDEOI system instruction requires the Rt field to be set to 0b11111 otherwise the instruction behaviour becomes CONSTRAINED UNPREDICTABLE. Currenly, its usage is encoded as a system register write, with a constant 0 value: write_sysreg_s(0, GICV5_OP_GIC_CDEOI) While compiling with GCC, the 0 constant value, through these asm constraints and modifiers ('x' modifier and 'Z' constraint combo): asm volatile(__msr_s(r, "%x0") : : "rZ" (__val)); forces the compiler to issue the XZR register for the MSR operation (ie that corresponds to Rt == 0b11111) issuing the right instruction encoding. Unfortunately LLVM does not yet understand that modifier/constraint combo so it ends up issuing a different register from XZR for the MSR source, which in turns means that it encodes the GIC CDEOI instruction wrongly and the instruction behaviour becomes CONSTRAINED UNPREDICTABLE that we must prevent. Add a conditional to write_sysreg_s() macro that detects whether it is passed a constant 0 value and issues an MSR write with XZR as source register - explicitly doing what the asm modifier/constraint is meant to achieve through constraints/modifiers, fixing the LLVM compilation issue. Fixes: 7ec80fb3f025 ("irqchip/gic-v5: Add GICv5 PPI support") Suggested-by: Catalin Marinas Signed-off-by: Lorenzo Pieralisi Acked-by: Marc Zyngier Cc: stable@vger.kernel.org Cc: Sascha Bischoff Cc: Will Deacon Cc: Mark Rutland Cc: Marc Zyngier Reviewed-by: Catalin Marinas Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/sysreg.h | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h index 6455db1b54fd..c231d2a3e515 100644 --- a/arch/arm64/include/asm/sysreg.h +++ b/arch/arm64/include/asm/sysreg.h @@ -1220,10 +1220,19 @@ __val; \ }) +/* + * The "Z" constraint combined with the "%x0" template should be enough + * to force XZR generation if (v) is a constant 0 value but LLVM does not + * yet understand that modifier/constraint combo so a conditional is required + * to nudge the compiler into using XZR as a source for a 0 constant value. + */ #define write_sysreg_s(v, r) do { \ u64 __val = (u64)(v); \ u32 __maybe_unused __check_r = (u32)(r); \ - asm volatile(__msr_s(r, "%x0") : : "rZ" (__val)); \ + if (__builtin_constant_p(__val) && __val == 0) \ + asm volatile(__msr_s(r, "xzr")); \ + else \ + asm volatile(__msr_s(r, "%x0") : : "r" (__val)); \ } while (0) /* From ea0d55ae4b3207c33691a73da3443b1fd379f1d2 Mon Sep 17 00:00:00 2001 From: Ada Couprie Diaz Date: Tue, 14 Oct 2025 10:25:36 +0100 Subject: [PATCH 2/2] 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); }