linux-kernel - [PATCH mm 19/22] kasan: respect KASAN_BIT

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Date:   Wed,  2 Mar 2022 17:36:39 +0100
From:   andrey.konovalov@...ux.dev
To:     Marco Elver <elver@...gle.com>,
        Alexander Potapenko <glider@...gle.com>
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH mm 19/22] kasan: respect KASAN_BIT_REPORTED in all reporting routines

From: Andrey Konovalov <andreyknvl@...gle.com>

Currently, only kasan_report() checks the KASAN_BIT_REPORTED and
KASAN_BIT_MULTI_SHOT flags.

Make other reporting routines check these flags as well.

Also add explanatory comments.

Note that the current->kasan_depth check is split out into
report_suppressed() and only called for kasan_report().

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 mm/kasan/report.c | 35 ++++++++++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 08631d873204..ef649f5cee29 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -381,12 +381,26 @@ static void print_memory_metadata(const void *addr)
 	}
 }
 
-static bool report_enabled(void)
+/*
+ * Used to suppress reports within kasan_disable/enable_current() critical
+ * sections, which are used for marking accesses to slab metadata.
+ */
+static bool report_suppressed(void)
 {
 #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
 	if (current->kasan_depth)
-		return false;
+		return true;
 #endif
+	return false;
+}
+
+/*
+ * Used to avoid reporting more than one KASAN bug unless kasan_multi_shot
+ * is enabled. Note that KASAN tests effectively enable kasan_multi_shot
+ * for their duration.
+ */
+static bool report_enabled(void)
+{
 	if (test_bit(KASAN_BIT_MULTI_SHOT, &kasan_flags))
 		return true;
 	return !test_and_set_bit(KASAN_BIT_REPORTED, &kasan_flags);
@@ -416,6 +430,14 @@ void kasan_report_invalid_free(void *ptr, unsigned long ip)
 	unsigned long flags;
 	struct kasan_report_info info;
 
+	/*
+	 * Do not check report_suppressed(), as an invalid-free cannot be
+	 * caused by accessing slab metadata and thus should not be
+	 * suppressed by kasan_disable/enable_current() critical sections.
+	 */
+	if (unlikely(!report_enabled()))
+		return;
+
 	start_report(&flags, true);
 
 	info.type = KASAN_REPORT_INVALID_FREE;
@@ -444,7 +466,7 @@ bool kasan_report(unsigned long addr, size_t size, bool is_write,
 	unsigned long irq_flags;
 	struct kasan_report_info info;
 
-	if (unlikely(!report_enabled())) {
+	if (unlikely(report_suppressed()) || unlikely(!report_enabled())) {
 		ret = false;
 		goto out;
 	}
@@ -473,6 +495,13 @@ void kasan_report_async(void)
 {
 	unsigned long flags;
 
+	/*
+	 * Do not check report_suppressed(), as kasan_disable/enable_current()
+	 * critical sections do not affect Hardware Tag-Based KASAN.
+	 */
+	if (unlikely(!report_enabled()))
+		return;
+
 	start_report(&flags, false);
 	pr_err("BUG: KASAN: invalid-access\n");
 	pr_err("Asynchronous fault: no details available\n");
-- 
2.25.1