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Message-ID: <CANpmjNOG=T8R=BXO8PUX3FJQnKQfPjNyLGJ0wG5G_4_mHwJ-gA@mail.gmail.com>
Date: Thu, 2 Mar 2023 12:18:21 +0100
From: Marco Elver <elver@...gle.com>
To: Alexander Potapenko <glider@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
dave.hansen@...ux.intel.com, hpa@...or.com,
akpm@...ux-foundation.org, dvyukov@...gle.com, nathan@...nel.org,
ndesaulniers@...gle.com, kasan-dev@...glegroups.com
Subject: Re: [PATCH 2/4] kmsan: another take at fixing memcpy tests
On Wed, 1 Mar 2023 at 15:39, 'Alexander Potapenko' via kasan-dev
<kasan-dev@...glegroups.com> wrote:
>
> 5478afc55a21 ("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 asm macro that just
> clobbers the memory, and add a test case for memcpy() that does not
> expect an error report.
>
> Also reflow kmsan_test.c with clang-format.
>
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> ---
> mm/kmsan/kmsan_test.c | 43 +++++++++++++++++++++++++++++++++++++------
> 1 file changed, 37 insertions(+), 6 deletions(-)
>
> diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
> index 088e21a48dc4b..cc98a3f4e0899 100644
> --- a/mm/kmsan/kmsan_test.c
> +++ b/mm/kmsan/kmsan_test.c
> @@ -407,6 +407,36 @@ 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.
> + */
> +#define DO_NOT_OPTIMIZE(var) asm("" ::: "memory")
That's just a normal "barrier()" - use that instead?
> +/*
> + * 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;
> +
> + // Ensure DO_NOT_OPTIMIZE() does not cause extra checks.
^^ this comment seems redundant now, given DO_NOT_OPTIMIZE() has a
comment (it's also using //-style comment).
> + 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 +450,7 @@ 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 +473,7 @@ 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 +497,14 @@ 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 +513,7 @@ 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 +545,7 @@ 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),
> --
> 2.39.2.722.g9855ee24e9-goog
>
> --
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