* [PATCH v2] x86/traps: avoid KMSAN bugs originating from handle_bug()
@ 2022-11-03 13:45 Alexander Potapenko
2022-11-03 14:32 ` Peter Zijlstra
0 siblings, 1 reply; 2+ messages in thread
From: Alexander Potapenko @ 2022-11-03 13:45 UTC (permalink / raw)
To: glider
Cc: linux-kernel, linux-mm, Andrew Morton, Borislav Petkov,
Dave Hansen, Ingo Molnar, Peter Zijlstra, Thomas Gleixner, x86
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@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Signed-off-by: Alexander Potapenko <glider@google.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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2] x86/traps: avoid KMSAN bugs originating from handle_bug()
2022-11-03 13:45 [PATCH v2] x86/traps: avoid KMSAN bugs originating from handle_bug() Alexander Potapenko
@ 2022-11-03 14:32 ` Peter Zijlstra
0 siblings, 0 replies; 2+ messages in thread
From: Peter Zijlstra @ 2022-11-03 14:32 UTC (permalink / raw)
To: Alexander Potapenko
Cc: linux-kernel, linux-mm, Andrew Morton, Borislav Petkov,
Dave Hansen, Ingo Molnar, Thomas Gleixner, x86
On Thu, Nov 03, 2022 at 02:45:15PM +0100, Alexander Potapenko wrote:
> 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@linux-foundation.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: x86@kernel.org
> Signed-off-by: Alexander Potapenko <glider@google.com>
>
> ---
>
> v2:
> - move the call to kmsan_unpoison_entry_regs() after the
> instrumentation_begin(), as suggested by Peter Zijlstra
Thanks!
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
^ permalink raw reply [flat|nested] 2+ messages in thread
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