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: 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 (cherry picked from commit ea0d55ae4b3207c33691a73da3443b1fd379f1d2) [ada.coupriediaz@arm.com: Fix conflict for v6.17 stable] Signed-off-by: Ada Couprie Diaz ada.coupriediaz@arm.com --- 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..db116a62ac95 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -832,6 +832,8 @@ 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();
@@ -842,10 +844,10 @@ 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); - } exit_to_user_mode(regs); }