From 2ea31e2e62bbc4d11c411eeb36f1b02841dbcab1 Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Mon, 6 Feb 2023 14:22:40 +1000
Subject: [PATCH] powerpc/64s/interrupt: Fix interrupt exit race with security
mitigation switch
References: bsc#1194869
Patch-mainline: v6.2-rc8
Git-commit: 2ea31e2e62bbc4d11c411eeb36f1b02841dbcab1
The RFI and STF security mitigation options can flip the
interrupt_exit_not_reentrant static branch condition concurrently with
the interrupt exit code which tests that branch.
Interrupt exit tests this condition to set MSR[EE|RI] for exit, then
again in the case a soft-masked interrupt is found pending, to recover
the MSR so the interrupt can be replayed before attempting to exit
again. If the condition changes between these two tests, the MSR and irq
soft-mask state will become corrupted, leading to warnings and possible
crashes. For example, if the branch is initially true then false,
MSR[EE] will be 0 but PACA_IRQ_HARD_DIS clear and EE may not get
enabled, leading to warnings in irq_64.c.
Fixes: 13799748b957 ("powerpc/64: use interrupt restart table to speed up return from interrupt")
Cc: stable@vger.kernel.org # v5.14+
Reported-by: Sachin Sant <sachinp@linux.ibm.com>
Tested-by: Sachin Sant <sachinp@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230206042240.92103-1-npiggin@gmail.com
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/kernel/interrupt.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index fc6631a80527..0ec1581619db 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -50,16 +50,18 @@ static inline bool exit_must_hard_disable(void)
*/
static notrace __always_inline bool prep_irq_for_enabled_exit(bool restartable)
{
+ bool must_hard_disable = (exit_must_hard_disable() || !restartable);
+
/* This must be done with RI=1 because tracing may touch vmaps */
trace_hardirqs_on();
- if (exit_must_hard_disable() || !restartable)
+ if (must_hard_disable)
__hard_EE_RI_disable();
#ifdef CONFIG_PPC64
/* This pattern matches prep_irq_for_idle */
if (unlikely(lazy_irq_pending_nocheck())) {
- if (exit_must_hard_disable() || !restartable) {
+ if (must_hard_disable) {
local_paca->irq_happened |= PACA_IRQ_HARD_DIS;
__hard_RI_enable();
}
--
2.40.0