[142/212] kasan: test: rework kmalloc_oob_right

Commit Message

Andrew Morton Sept. 2, 2021, 9:57 p.m. UTC

From: Andrey Konovalov <[e-mail]>
Subject: kasan: test: rework kmalloc_oob_right

Patch series "kasan: test: avoid crashing the kernel with HW_TAGS", v2.

KASAN tests do out-of-bounds and use-after-free accesses.  Running the
tests works fine for the GENERIC mode, as it uses qurantine and redzones. 
But the HW_TAGS mode uses neither, and running the tests might crash the
kernel.

Rework the tests to avoid corrupting kernel memory.


This patch (of 8):

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.

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/47[e-mail]
Signed-off-by: Andrey Konovalov <[e-mail]>
Reviewed-by: Marco Elver <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Alexander Potapenko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 lib/test_kasan.c |   20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

Patch

--- a/lib/test_kasan.c~kasan-test-rework-kmalloc_oob_right
+++ a/lib/test_kasan.c
@@ -122,12 +122,28 @@  static void kasan_test_exit(struct kunit
 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);
 }