linux-kernel - [PATCH v6 5/5] mm: kasan: Do not panic if both panic_on_warn and kasan

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Message-Id: <20200418031833.234942-6-davidgow@google.com>
Date:   Fri, 17 Apr 2020 20:18:33 -0700
From:   David Gow <davidgow@...gle.com>
To:     trishalfonso@...gle.com, brendanhiggins@...gle.com,
        aryabinin@...tuozzo.com, dvyukov@...gle.com, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org
Cc:     David Gow <davidgow@...gle.com>, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, kunit-dev@...glegroups.com,
        linux-kselftest@...r.kernel.org
Subject: [PATCH v6 5/5] mm: kasan: Do not panic if both panic_on_warn and
 kasan_multishot set

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@...gle.com>
---
 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 0c206bbf9cb3..79fe23bd4f60 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -94,7 +94,7 @@ 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)) {
 		/*
 		 * This thread may hit another WARN() in the panic path.
 		 * Resetting this prevents additional WARN() from panicking the
-- 
2.26.1.301.g55bc3eb7cb9-goog