linux-kernel - [PATCH 1/8] kasan: test: rework kmalloc_oob

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Date:   Wed, 11 Aug 2021 21:21:17 +0200
From:   andrey.konovalov@...ux.dev
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/8] kasan: test: rework kmalloc_oob_right

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

Rework kmalloc_oob_right() to do these bad access checks:

1. An unaligned access one byte past the requested kmalloc size
   (can only be detected by KASAN_GENERIC).
2. An aligned access into the first out-of-bounds granule that falls
   within the aligned kmalloc object.
3. Out-of-bounds access past the aligned kmalloc object.

Test #3 deliberately uses a read access to avoid corrupting memory.
Otherwise, this test might lead to crashes with the HW_TAGS mode, as it
neither uses quarantine nor redzones.

Signed-off-by: Andrey Konovalov <andreyknvl@...il.com>
---
 lib/test_kasan.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 8f7b0b2f6e11..1bc3cdd2957f 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -122,12 +122,28 @@ static void kasan_test_exit(struct kunit *test)
 static void kmalloc_oob_right(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 123;
+	size_t size = 128 - KASAN_GRANULE_SIZE - 5;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
-	KUNIT_EXPECT_KASAN_FAIL(test, ptr[size + OOB_TAG_OFF] = 'x');
+	/*
+	 * An unaligned access past the requested kmalloc size.
+	 * Only generic KASAN can precisely detect these.
+	 */
+	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
+		KUNIT_EXPECT_KASAN_FAIL(test, ptr[size] = 'x');
+
+	/*
+	 * An aligned access into the first out-of-bounds granule that falls
+	 * within the aligned kmalloc object.
+	 */
+	KUNIT_EXPECT_KASAN_FAIL(test, ptr[size + 5] = 'y');
+
+	/* Out-of-bounds access past the aligned kmalloc object. */
+	KUNIT_EXPECT_KASAN_FAIL(test, ptr[0] =
+					ptr[size + KASAN_GRANULE_SIZE + 5]);
+
 	kfree(ptr);
 }
 
-- 
2.25.1