The patch titled
Subject: kmsan: prevent optimizations in memcpy tests
has been added to the -mm mm-unstable branch. Its filename is
kmsan-prevent-optimizations-in-memcpy-tests.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kmsan-prevent-optimizations-in-memcpy-tests.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Alexander Potapenko <glider@xxxxxxxxxx>
Subject: kmsan: prevent optimizations in memcpy tests
Date: Mon, 11 Sep 2023 16:57:00 +0200
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@xxxxxxxxxx
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
Acked-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kmsan/kmsan_test.c | 41 +++++++++++++++-------------------------
1 file changed, 16 insertions(+), 25 deletions(-)
--- a/mm/kmsan/kmsan_test.c~kmsan-prevent-optimizations-in-memcpy-tests
+++ a/mm/kmsan/kmsan_test.c
@@ -407,33 +407,25 @@ static void test_printk(struct kunit *te
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_align
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_unali
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_unali
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_unali
\
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)); \
_
Patches currently in -mm which might be from glider@xxxxxxxxxx are
kmsan-simplify-kmsan_internal_memmove_metadata.patch
kmsan-prevent-optimizations-in-memcpy-tests.patch
kmsan-merge-test_memcpy_aligned_to_unaligned2-together.patch
kmsan-introduce-test_memcpy_initialized_gap.patch
