Commit d3402925 authored by Alexander Potapenko's avatar Alexander Potapenko Committed by Andrew Morton
Browse files

kmsan: another take at fixing memcpy tests 

commit 5478afc5 ("kmsan: fix memcpy tests") uses OPTIMIZER_HIDE_VAR()
to hide the uninitialized var from the compiler optimizations.

However OPTIMIZER_HIDE_VAR(uninit) enforces an immediate check of @uninit,
so memcpy tests did not actually check the behavior of memcpy(), because
they always contained a KMSAN report.

Replace OPTIMIZER_HIDE_VAR() with a file-local macro that just clobbers
the memory with a barrier(), and add a test case for memcpy() that does
not expect an error report.

Also reflow kmsan_test.c with clang-format.

Link: https://lkml.kernel.org/r/20230303141433.3422671-2-glider@google.com


Signed-off-by: default avatarAlexander Potapenko <glider@google.com>
Reviewed-by: default avatarMarco Elver <elver@google.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 6dc4bd4e

mm/kmsan/kmsan_test.c

+38 −6
Original line number Diff line number Diff line
@@ -407,6 +407,37 @@ static void test_printk(struct kunit *test) 
	KUNIT_EXPECT_TRUE(test, report_matches(&expect));

}



/*

 * Prevent the compiler from optimizing @var away. Without this, Clang may

 * notice that @var is uninitialized and drop memcpy() calls that use it.

 *

 * There is OPTIMIZER_HIDE_VAR() in linux/compier.h that we cannot use here,

 * because it is implemented as inline assembly receiving @var as a parameter

 * and will enforce a KMSAN check. Same is true for e.g. barrier_data(var).

 */

#define DO_NOT_OPTIMIZE(var) barrier()



/*

 * Test case: ensure that memcpy() correctly copies initialized values.

 * Also serves as a regression test to ensure DO_NOT_OPTIMIZE() does not cause

 * extra checks.

 */

static void test_init_memcpy(struct kunit *test)

{

	EXPECTATION_NO_REPORT(expect);

	volatile int src;

	volatile int dst = 0;



	DO_NOT_OPTIMIZE(src);

	src = 1;

	kunit_info(

		test,

		"memcpy()ing aligned initialized src to aligned dst (no reports)\n");

	memcpy((void *)&dst, (void *)&src, sizeof(src));

	kmsan_check_memory((void *)&dst, sizeof(dst));

	KUNIT_EXPECT_TRUE(test, report_matches(&expect));

}



/*

 * Test case: ensure that memcpy() correctly copies uninitialized values between

 * aligned `src` and `dst`.
@@ -420,7 +451,7 @@ static void test_memcpy_aligned_to_aligned(struct kunit *test) 
	kunit_info(

		test,

		"memcpy()ing aligned uninit src to aligned dst (UMR report)\n");

	OPTIMIZER_HIDE_VAR(uninit_src);

	DO_NOT_OPTIMIZE(uninit_src);

	memcpy((void *)&dst, (void *)&uninit_src, sizeof(uninit_src));

	kmsan_check_memory((void *)&dst, sizeof(dst));

	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
@@ -443,7 +474,7 @@ static void test_memcpy_aligned_to_unaligned(struct kunit *test) 
	kunit_info(

		test,

		"memcpy()ing aligned uninit src to unaligned dst (UMR report)\n");

	OPTIMIZER_HIDE_VAR(uninit_src);

	DO_NOT_OPTIMIZE(uninit_src);

	memcpy((void *)&dst[1], (void *)&uninit_src, sizeof(uninit_src));

	kmsan_check_memory((void *)dst, 4);

	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
@@ -467,13 +498,14 @@ static void test_memcpy_aligned_to_unaligned2(struct kunit *test) 
	kunit_info(

		test,

		"memcpy()ing aligned uninit src to unaligned dst - part 2 (UMR report)\n");

	OPTIMIZER_HIDE_VAR(uninit_src);

	DO_NOT_OPTIMIZE(uninit_src);

	memcpy((void *)&dst[1], (void *)&uninit_src, sizeof(uninit_src));

	kmsan_check_memory((void *)&dst[4], sizeof(uninit_src));

	KUNIT_EXPECT_TRUE(test, report_matches(&expect));

}



static noinline void fibonacci(int *array, int size, int start) {

static noinline void fibonacci(int *array, int size, int start)

{

	if (start < 2 || (start == size))

		return;

	array[start] = array[start - 1] + array[start - 2];
@@ -482,8 +514,7 @@ static noinline void fibonacci(int *array, int size, int start) { 


static void test_long_origin_chain(struct kunit *test)

{

	EXPECTATION_UNINIT_VALUE_FN(expect,

				    "test_long_origin_chain");

	EXPECTATION_UNINIT_VALUE_FN(expect, "test_long_origin_chain");

	/* (KMSAN_MAX_ORIGIN_DEPTH * 2) recursive calls to fibonacci(). */

	volatile int accum[KMSAN_MAX_ORIGIN_DEPTH * 2 + 2];

	int last = ARRAY_SIZE(accum) - 1;
@@ -515,6 +546,7 @@ static struct kunit_case kmsan_test_cases[] = { 
	KUNIT_CASE(test_uaf),

	KUNIT_CASE(test_percpu_propagate),

	KUNIT_CASE(test_printk),

	KUNIT_CASE(test_init_memcpy),

	KUNIT_CASE(test_memcpy_aligned_to_aligned),

	KUNIT_CASE(test_memcpy_aligned_to_unaligned),

	KUNIT_CASE(test_memcpy_aligned_to_unaligned2),