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From:   andrey.konovalov@linux.dev
To:     Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH mm 22/22] kasan: disable LOCKDEP when printing reports
Date:   Wed,  2 Mar 2022 17:36:42 +0100
Message-Id: <c48a2a3288200b07e1788b77365c2f02784cfeb4.1646237226.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

If LOCKDEP detects a bug while KASAN is printing a report and if
panic_on_warn is set, KASAN will not be able to finish.
Disable LOCKDEP while KASAN is printing a report.

See https://bugzilla.kernel.org/show_bug.cgi?id=202115 for an example
of the issue.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/kasan/report.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index c9bfffe931b4..199d77cce21a 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -13,6 +13,7 @@
 #include <linux/ftrace.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
+#include <linux/lockdep.h>
 #include <linux/mm.h>
 #include <linux/printk.h>
 #include <linux/sched.h>
@@ -148,6 +149,8 @@ static void start_report(unsigned long *flags, bool sync)
 	disable_trace_on_warning();
 	/* Update status of the currently running KASAN test. */
 	update_kunit_status(sync);
+	/* Do not allow LOCKDEP mangling KASAN reports. */
+	lockdep_off();
 	/* Make sure we don't end up in loop. */
 	kasan_disable_current();
 	spin_lock_irqsave(&report_lock, *flags);
@@ -160,12 +163,13 @@ static void end_report(unsigned long *flags, void *addr)
 		trace_error_report_end(ERROR_DETECTOR_KASAN,
 				       (unsigned long)addr);
 	pr_err("==================================================================\n");
-	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 	spin_unlock_irqrestore(&report_lock, *flags);
 	if (panic_on_warn && !test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 		panic("panic_on_warn set ...\n");
 	if (kasan_arg_fault == KASAN_ARG_FAULT_PANIC)
 		panic("kasan.fault=panic set ...\n");
+	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
+	lockdep_on();
 	kasan_enable_current();
 }
 
-- 
2.25.1