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Message-ID: <20221103134515.1934867-1-glider@google.com>
Date: Thu, 3 Nov 2022 14:45:15 +0100
From: Alexander Potapenko <glider@...gle.com>
To: glider@...gle.com
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Andrew Morton <akpm@...ux-foundation.org>,
Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Subject: [PATCH v2] x86/traps: avoid KMSAN bugs originating from handle_bug()
There is a case in exc_invalid_op handler that is executed outside the
irqentry_enter()/irqentry_exit() region when an UD2 instruction is used
to encode a call to __warn().
In that case the `struct pt_regs` passed to the interrupt handler is
never unpoisoned by KMSAN (this is normally done in irqentry_enter()),
which leads to false positives inside handle_bug().
Use kmsan_unpoison_entry_regs() to explicitly unpoison those registers
before using them.
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86@...nel.org
Signed-off-by: Alexander Potapenko <glider@...gle.com>
---
v2:
- move the call to kmsan_unpoison_entry_regs() after the
instrumentation_begin(), as suggested by Peter Zijlstra
---
arch/x86/kernel/traps.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 178015a820f08..66701b4d99acd 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -15,6 +15,7 @@
#include <linux/context_tracking.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
+#include <linux/kmsan.h>
#include <linux/spinlock.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
@@ -308,6 +309,13 @@ static noinstr bool handle_bug(struct pt_regs *regs)
* All lies, just get the WARN/BUG out.
*/
instrumentation_begin();
+
+ /*
+ * Normally @regs are unpoisoned by irqentry_enter(), but handle_bug()
+ * is a rare case that uses @regs without passing them to
+ * irqentry_enter().
+ */
+ kmsan_unpoison_entry_regs(regs);
/*
* Since we're emulating a CALL with exceptions, restore the interrupt
* state to what it was at the exception site.
--
2.38.1.273.g43a17bfeac-goog
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