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From: Rohan McLure <rmclure@linux.ibm.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: Rohan McLure <rmclure@linux.ibm.com>,
	Nicholas Piggin <npiggin@gmail.com>
Subject: [PATCH 2/2] powerpc/64: Only warn for kuap locked when KCSAN not present
Date: Thu,  4 Apr 2024 15:45:36 +1100	[thread overview]
Message-ID: <20240404044535.642122-4-rmclure@linux.ibm.com> (raw)
In-Reply-To: <20240404044535.642122-2-rmclure@linux.ibm.com>

Arbitrary instrumented locations, including syscall handlers, can call
arch_local_irq_restore() transitively when KCSAN is enabled, and in turn
also replay_soft_interrupts_irqrestore(). The precondition on entry to
this routine that is checked is that KUAP is enabled (user access
prohibited). Failure to meet this condition only triggers a warning
however, and afterwards KUAP is enabled anyway. That is, KUAP being
disabled on entry is in fact permissable, but not possible on an
uninstrumented kernel.

Disable this assertion only when KCSAN is enabled.

Suggested-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
---
 arch/powerpc/kernel/irq_64.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/irq_64.c b/arch/powerpc/kernel/irq_64.c
index d5c48d1b0a31..18b2048389a2 100644
--- a/arch/powerpc/kernel/irq_64.c
+++ b/arch/powerpc/kernel/irq_64.c
@@ -189,7 +189,8 @@ static inline __no_kcsan void replay_soft_interrupts_irqrestore(void)
 	 * and re-locking AMR but we shouldn't get here in the first place,
 	 * hence the warning.
 	 */
-	kuap_assert_locked();
+	if (!IS_ENABLED(CONFIG_KCSAN))
+		kuap_assert_locked();
 
 	if (kuap_state != AMR_KUAP_BLOCKED)
 		set_kuap(AMR_KUAP_BLOCKED);
-- 
2.44.0


  reply	other threads:[~2024-04-04  4:47 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-04-04  4:45 [PATCH 1/2] powerpc: Apply __always_inline to interrupt_{enter,exit}_prepare() Rohan McLure
2024-04-04  4:45 ` Rohan McLure [this message]
2024-04-04  6:14   ` [PATCH 2/2] powerpc/64: Only warn for kuap locked when KCSAN not present Christophe Leroy
2024-04-11  1:53     ` Rohan McLure
2024-04-04  6:14 ` [PATCH 1/2] powerpc: Apply __always_inline to interrupt_{enter,exit}_prepare() Christophe Leroy

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