Commit 0be7b2c2 authored by Alexander Potapenko's avatar Alexander Potapenko Committed by Andrew Morton
Browse files

kmsan: prevent optimizations in memcpy tests 

Clang 18 learned to optimize away memcpy() calls of small uninitialized
scalar values.  To ensure that memcpy tests in kmsan_test.c still perform
calls to memcpy() (which KMSAN replaces with __msan_memcpy()), declare a
separate memcpy_noinline() function with volatile parameters, which won't
be optimized.

Also retire DO_NOT_OPTIMIZE(), as memcpy_noinline() is apparently enough.

Link: https://lkml.kernel.org/r/20230911145702.2663753-2-glider@google.com


Signed-off-by: default avatarAlexander Potapenko <glider@google.com>
Acked-by: default avatarMarco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent be1ab60e

mm/kmsan/kmsan_test.c

+16 −25
Original line number Diff line number Diff line
@@ -407,33 +407,25 @@ 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()

/* Prevent the compiler from inlining a memcpy() call. */

static noinline void *memcpy_noinline(volatile void *dst,

				      const volatile void *src, size_t size)

{

	return memcpy((void *)dst, (const void *)src, size);

}



/*

 * 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.

 */

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

static void test_init_memcpy(struct kunit *test)

{

	EXPECTATION_NO_REPORT(expect);

	volatile int src;

	volatile int dst = 0;

	volatile long long src;

	volatile long long 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));

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

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

	KUNIT_EXPECT_TRUE(test, report_matches(&expect));

}
@@ -451,8 +443,7 @@ static void test_memcpy_aligned_to_aligned(struct kunit *test) 
	kunit_info(

		test,

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

	DO_NOT_OPTIMIZE(uninit_src);

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

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

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

	KUNIT_EXPECT_TRUE(test, report_matches(&expect));

}
@@ -474,8 +465,9 @@ static void test_memcpy_aligned_to_unaligned(struct kunit *test) 
	kunit_info(

		test,

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

	DO_NOT_OPTIMIZE(uninit_src);

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

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

	memcpy_noinline((void *)&dst[1], (void *)&uninit_src,

			sizeof(uninit_src));

	kmsan_check_memory((void *)dst, 4);

	KUNIT_EXPECT_TRUE(test, report_matches(&expect));

}
@@ -498,8 +490,8 @@ 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");

	DO_NOT_OPTIMIZE(uninit_src);

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

	memcpy_noinline((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));

}
@@ -513,7 +505,6 @@ static void test_memcpy_aligned_to_unaligned2(struct kunit *test) 
                                                                            \

		kunit_info(test,                                            \

			   "memset" #size "() should initialize memory\n"); \

		DO_NOT_OPTIMIZE(uninit);                                    \

		memset##size((uint##size##_t *)&uninit, 0, 1);              \

		kmsan_check_memory((void *)&uninit, sizeof(uninit));        \

		KUNIT_EXPECT_TRUE(test, report_matches(&expect));           \