mm: kasan: do not panic if both panic_on_warn and kasan_multishot set

commit d6e893addabaab95bded928d3a7f2b0b744696d7 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@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Patricia Alfonso <trishalfonso@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20200915035828.570483-6-davidgow@google.com
Link: https://lkml.kernel.org/r/20200910070331.3358048-6-davidgow@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 621782100eaa0f81d930799c6899d598db390550..a05ff1922d499d2fe9ea641b522cb267dc8f17f6 100644 (file)
--- 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();
 }