[PATCH 5.4 03/17] mm: kasan: do not panic if both panic_on_warn and kasan_multishot set

[Eric Biggers]

From: David Gow <davidgow@xxxxxxxxxx>

commit be4f1ae978ffe98cc95ec49ceb95386fb4474974 upstream.

KASAN errors will currently trigger a panic when panic_on_warn is set.
This renders kasan_multishot useless, as further KASAN errors won't be
reported if the kernel has already paniced.  By making kasan_multishot
disable this behaviour for KASAN errors, we can still have the benefits of
panic_on_warn for non-KASAN warnings, yet be able to use kasan_multishot.

This is particularly important when running KASAN tests, which need to
trigger multiple KASAN errors: previously these would panic the system if
panic_on_warn was set, now they can run (and will panic the system should
non-KASAN warnings show up).

Signed-off-by: David Gow <davidgow@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reviewed-by: Brendan Higgins <brendanhiggins@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Patricia Alfonso <trishalfonso@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200915035828.570483-6-davidgow@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20200910070331.3358048-6-davidgow@xxxxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
 mm/kasan/report.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 621782100eaa0..a05ff1922d499 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -92,7 +92,7 @@ static void end_report(unsigned long *flags)
 	pr_err("==================================================================\n");
 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 	spin_unlock_irqrestore(&report_lock, *flags);
-	if (panic_on_warn)
+	if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 		panic("panic_on_warn set ...\n");
 	kasan_enable_current();
 }
-- 
2.39.1