EL0 exception handlers should always call `exit_to_user_mode()` with interrupts unmasked. When handling a completed single-step, we skip the if block and `local_daif_restore(DAIF_PROCCTX)` never gets called, which ends up calling `exit_to_user_mode()` with interrupts masked.
This is broken if pNMI is in use, as `do_notify_resume()` will try to enable interrupts, but `local_irq_enable()` will only change the PMR, leaving interrupts masked via DAIF.
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: stable@vger.kernel.org # 6.17 Signed-off-by: Ada Couprie Diaz ada.coupriediaz@arm.com ---- This was already broken in a similar fashion in kernels prior to v6.17, as `local_daif_restore()` was called _after_ the debug handlers, with some calling `send_user_sigtrap()` which would unmask interrupts via PMR while leaving them masked by DAIF. --- 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 2b0c5925502e..780cbcf12695 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -832,6 +832,7 @@ 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();
@@ -842,10 +843,11 @@ 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); - } + exit_to_user_mode(regs); }
base-commit: 449d48b1b99fdaa076166e200132705ac2bee711