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 <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra (Intel) <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Signed-off-by: Alexander Potapenko <[email protected]>
---
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
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 <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Peter Zijlstra (Intel) <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: [email protected]
> Signed-off-by: Alexander Potapenko <[email protected]>
>
> ---
>
> v2:
> - move the call to kmsan_unpoison_entry_regs() after the
> instrumentation_begin(), as suggested by Peter Zijlstra
Thanks!
Acked-by: Peter Zijlstra (Intel) <[email protected]>