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/cover.1628779805.git.andreyknvl@gmail.com
Link: https://lkml.kernel.org/r/474aa8b7b538c6737a4c6d0090350af2e1776bef.1628779805.git.andreyknvl@gmail.com
Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 8f7b0b2..1bc3cdd 100644 (file)
--- 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);
 }