[PATCH] gpu/tests/buddy: Stop a test when gpu_buddy_init() fails

[Yuqiang Sun <izaiahsun@gmail.com>]

Three tests check gpu_buddy_init() with KUNIT_EXPECT_FALSE(), which only
records the failure, and go on to allocate from the allocator and to
call gpu_buddy_fini(). When gpu_buddy_init() fails, it has freed what it
allocated (or never allocated it), and the gpu_buddy is on the test's
stack, uninitialized, so the test then works on freed or garbage
pointers. The other tests in the file use KUNIT_ASSERT_FALSE(), which
stops the test case.

Use KUNIT_ASSERT_FALSE() in gpu_test_buddy_alloc_clear(),
gpu_test_buddy_alloc_contiguous() and gpu_test_buddy_alloc_limit() too.
In gpu_test_buddy_alloc_clear() each later call follows a
gpu_buddy_fini(), so stopping there leaves nothing allocated.

Found by kbound, a static analysis prototype for ownership mismatches at
kernel interfaces. Run-tested on QEMU (x86_64, KVM) with KASAN and the
suite as a module, with failslab limited to allocations under
gpu_buddy_init() and set to fail the first call's 1st to 5th allocation.
Before this patch, all 15 runs (three tests, five allocations) end in a
general protection fault, five of them after KASAN slab-use-after-free
reports in gpu_buddy_alloc_blocks() or __gpu_buddy_alloc_range(). With
it, each stops at the assertion, and the whole suite still passes
without injection.

Fixes: 932da861956a ("drm: selftest: convert drm_buddy selftest to KUnit")
Fixes: a64056bb5a32 ("drm/tests/drm_buddy: add alloc_contiguous test")
Fixes: c1696bf8d5f5 ("drm/tests: Add a test case for drm buddy clear allocation")
Signed-off-by: Yuqiang Sun <izaiahsun@gmail.com>
---

Notes:
    The bug was found with kbound, a research static analysis prototype.
    The patch, the changelog and the test setup were written with the help
    of an AI coding assistant (Claude); I have reviewed and tested them as
    described above.
    
    The runs were on mainline d135ab453a74; the test file is the same there
    and in drm-misc-next, which this patch is based on, except for an
    unrelated hunk in gpu_test_buddy_alloc_contiguous().

 drivers/gpu/tests/gpu_buddy_test.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/tests/gpu_buddy_test.c b/drivers/gpu/tests/gpu_buddy_test.c
index 2c6f1da1a6d1..e85d83e42bb7 100644
--- a/drivers/gpu/tests/gpu_buddy_test.c
+++ b/drivers/gpu/tests/gpu_buddy_test.c
@@ -975,7 +975,7 @@ static void gpu_test_buddy_alloc_clear(struct kunit *test)
 	LIST_HEAD(clean);
 
 	mm_size = SZ_4K << max_order;
-	KUNIT_EXPECT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
+	KUNIT_ASSERT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
 
 	KUNIT_EXPECT_EQ(test, mm.max_order, max_order);
 
@@ -1035,7 +1035,7 @@ static void gpu_test_buddy_alloc_clear(struct kunit *test)
 	gpu_buddy_free_list(&mm, &dirty, 0);
 	gpu_buddy_fini(&mm);
 
-	KUNIT_EXPECT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
+	KUNIT_ASSERT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
 
 	/*
 	 * Create a new mm. Intentionally fragment the address space by creating
@@ -1095,7 +1095,7 @@ static void gpu_test_buddy_alloc_clear(struct kunit *test)
 	 */
 	mm_size = (SZ_4K << max_order) + (SZ_4K << (max_order - 2));
 
-	KUNIT_EXPECT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
+	KUNIT_ASSERT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
 	KUNIT_EXPECT_EQ(test, mm.max_order, max_order);
 	KUNIT_ASSERT_FALSE_MSG(test, gpu_buddy_alloc_blocks(&mm, 0, SZ_4K << max_order,
 							    4 * ps, ps, &allocated,
@@ -1123,7 +1123,7 @@ static void gpu_test_buddy_alloc_clear(struct kunit *test)
 	 * and the split blocks should be merged back to their original size, so
 	 * clear_avail must drop to 0.
 	 */
-	KUNIT_EXPECT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
+	KUNIT_ASSERT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
 	KUNIT_EXPECT_EQ(test, mm.max_order, max_order);
 
 	n_pages = mm_size / ps;
@@ -1147,7 +1147,7 @@ static void gpu_test_buddy_alloc_clear(struct kunit *test)
 	 * the split blocks should be merged back to their original size, so the
 	 * whole address space (clear_avail) must equal mm_size.
 	 */
-	KUNIT_EXPECT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
+	KUNIT_ASSERT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
 	KUNIT_EXPECT_EQ(test, mm.max_order, max_order);
 
 	for (i = 0; i < n_pages; i++) {
@@ -1176,7 +1176,7 @@ static void gpu_test_buddy_alloc_contiguous(struct kunit *test)
 	LIST_HEAD(right);
 	LIST_HEAD(allocated);
 
-	KUNIT_EXPECT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
+	KUNIT_ASSERT_FALSE(test, gpu_buddy_init(&mm, mm_size, ps));
 
 	/*
 	 * Idea is to fragment the address space by alternating block
@@ -1490,7 +1490,7 @@ static void gpu_test_buddy_alloc_limit(struct kunit *test)
 	LIST_HEAD(allocated);
 	struct gpu_buddy mm;
 
-	KUNIT_EXPECT_FALSE(test, gpu_buddy_init(&mm, size, SZ_4K));
+	KUNIT_ASSERT_FALSE(test, gpu_buddy_init(&mm, size, SZ_4K));
 
 	KUNIT_EXPECT_EQ_MSG(test, mm.max_order, GPU_BUDDY_MAX_ORDER,
 			    "mm.max_order(%d) != %d\n", mm.max_order,

base-commit: a1e63ab695ad76850ab9787b9eb6aab695dc2965
-- 
2.53.0