[PATCH v2 8/8] selftest/mm: ksm_functional_tests: Add PROT_NONE test

David Hildenbrand
2023-08-01T12:51:07Z

Let's test whether merging and unmerging in PROT_NONE areas works as
expected.

Pass a page protection to mmap_and_merge_range(), which will trigger
an mprotect() after writing to the pages, but before enabling merging.

Make sure that unsharing works as expected, by performing a ptrace write
(using /proc/self/mem) and by setting MADV_UNMERGEABLE.

Note that this implicitly tests that ptrace writes in an inaccessible
(PROT_NONE) mapping work as expected.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
.../selftests/mm/ksm_functional_tests.c | 59 ++++++++++++++++---
1 file changed, 52 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/mm/ksm_functional_tests.c b/tools/testing/selftests/mm/ksm_functional_tests.c
index cb63b600cb4f..8fa4889ab4f3 100644
--- a/tools/testing/selftests/mm/ksm_functional_tests.c
+++ b/tools/testing/selftests/mm/ksm_functional_tests.c
@@ -27,6 +27,7 @@
#define KiB 1024u
#define MiB (1024 * KiB)

+static int mem_fd;
static int ksm_fd;
static int ksm_full_scans_fd;
static int proc_self_ksm_stat_fd;
@@ -144,7 +145,8 @@ static int ksm_unmerge(void)
return 0;
}

-static char *mmap_and_merge_range(char val, unsigned long size, bool use_prctl)
+static char *mmap_and_merge_range(char val, unsigned long size, int prot,
+ bool use_prctl)
{
char *map;
int ret;
@@ -176,6 +178,11 @@ static char *mmap_and_merge_range(char val, unsigned long size, bool use_prctl)
/* Make sure each page contains the same values to merge them. */
memset(map, val, size);

+ if (mprotect(map, size, prot)) {
+ ksft_test_result_skip("mprotect() failed\n");
+ goto unmap;
+ }
+
if (use_prctl) {
ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
if (ret < 0 && errno == EINVAL) {
@@ -218,7 +225,7 @@ static void test_unmerge(void)

ksft_print_msg("[RUN] %s\n", __func__);

- map = mmap_and_merge_range(0xcf, size, false);
+ map = mmap_and_merge_range(0xcf, size, PROT_READ | PROT_WRITE, false);
if (map == MAP_FAILED)
return;

@@ -256,7 +263,7 @@ static void test_unmerge_zero_pages(void)
}

/* Let KSM deduplicate zero pages. */
- map = mmap_and_merge_range(0x00, size, false);
+ map = mmap_and_merge_range(0x00, size, PROT_READ | PROT_WRITE, false);
if (map == MAP_FAILED)
return;

@@ -304,7 +311,7 @@ static void test_unmerge_discarded(void)

ksft_print_msg("[RUN] %s\n", __func__);

- map = mmap_and_merge_range(0xcf, size, false);
+ map = mmap_and_merge_range(0xcf, size, PROT_READ | PROT_WRITE, false);
if (map == MAP_FAILED)
return;

@@ -336,7 +343,7 @@ static void test_unmerge_uffd_wp(void)

ksft_print_msg("[RUN] %s\n", __func__);

- map = mmap_and_merge_range(0xcf, size, false);
+ map = mmap_and_merge_range(0xcf, size, PROT_READ | PROT_WRITE, false);
if (map == MAP_FAILED)
return;

@@ -479,7 +486,7 @@ static void test_prctl_unmerge(void)

ksft_print_msg("[RUN] %s\n", __func__);

- map = mmap_and_merge_range(0xcf, size, true);
+ map = mmap_and_merge_range(0xcf, size, PROT_READ | PROT_WRITE, true);
if (map == MAP_FAILED)
return;

@@ -494,9 +501,42 @@ static void test_prctl_unmerge(void)
munmap(map, size);
}

+static void test_prot_none(void)
+{
+ const unsigned int size = 2 * MiB;
+ char *map;
+ int i;
+
+ ksft_print_msg("[RUN] %s\n", __func__);
+
+ map = mmap_and_merge_range(0x11, size, PROT_NONE, false);
+ if (map == MAP_FAILED)
+ goto unmap;
+
+ /* Store a unique value in each page on one half using ptrace */
+ for (i = 0; i < size / 2; i += pagesize) {
+ lseek(mem_fd, (uintptr_t) map + i, SEEK_SET);
+ if (write(mem_fd, &i, sizeof(size)) != sizeof(size)) {
+ ksft_test_result_fail("ptrace write failed\n");
+ goto unmap;
+ }
+ }
+
+ /* Trigger unsharing on the other half. */
+ if (madvise(map + size / 2, size / 2, MADV_UNMERGEABLE)) {
+ ksft_test_result_fail("MADV_UNMERGEABLE failed\n");
+ goto unmap;
+ }
+
+ ksft_test_result(!range_maps_duplicates(map, size),
+ "Pages were unmerged\n");
+unmap:
+ munmap(map, size);
+}
+
int main(int argc, char **argv)
{
- unsigned int tests = 6;
+ unsigned int tests = 7;
int err;

#ifdef __NR_userfaultfd
@@ -508,6 +548,9 @@ int main(int argc, char **argv)

pagesize = getpagesize();

+ mem_fd = open("/proc/self/mem", O_RDWR);
+ if (mem_fd < 0)
+ ksft_exit_fail_msg("opening /proc/self/mem failed\n");
ksm_fd = open("/sys/kernel/mm/ksm/run", O_RDWR);
if (ksm_fd < 0)
ksft_exit_skip("open(\"/sys/kernel/mm/ksm/run\") failed\n");
@@ -529,6 +572,8 @@ int main(int argc, char **argv)
test_unmerge_uffd_wp();
#endif

+ test_prot_none();
+
test_prctl();
test_prctl_fork();
test_prctl_unmerge();
--
2.41.0