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Howlett" , Matthew Wilcox , Vlastimil Babka , "Paul E . McKenney" , Jann Horn , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Shuah Khan , linux-kselftest@vger.kernel.org, linux-api@vger.kernel.org, John Hubbard , Juan Yescas , Kalesh Singh Subject: [PATCH 4/4] tools/selftests: add file/shmem-backed mapping guard region tests Date: Thu, 13 Feb 2025 18:17:03 +0000 Message-ID: <90c16bec5fcaafcd1700dfa3e9988c3e1aa9ac1d.1739469950.git.lorenzo.stoakes@oracle.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: References: X-ClientProxiedBy: LO4P265CA0232.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:315::14) To BYAPR10MB3366.namprd10.prod.outlook.com (2603:10b6:a03:14f::25) Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR10MB3366:EE_|PH8PR10MB6387:EE_ X-MS-Office365-Filtering-Correlation-Id: aeb984a6-d8ed-45f7-34d6-08dd4c5ad928 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|366016|1800799024; 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In addition to testing all of the existing guard region functionality that is currently tested against anonymous mappings against file-backed and shmem mappings (except those which are exclusive to anonymous mapping), we now also: * Test that MADV_SEQUENTIAL does not cause unexpected readahead behaviour. * Test that MAP_PRIVATE behaves as expected with guard regions installed in both a shared and private mapping of an fd. * Test that a read-only file can correctly establish guard regions. * Test a probable fault-around case does not interfere with guard regions (or vice-versa). * Test that truncation does not eliminate guard regions. * Test that hole punching functions as expected in the presence of guard regions. * Test that a read-only mapping of a memfd write sealed mapping can have guard regions established within it and function correctly without violation of the seal. * Test that guard regions installed into a mapping of the anonymous zero page function correctly. Signed-off-by: Lorenzo Stoakes --- tools/testing/selftests/mm/guard-regions.c | 595 +++++++++++++++++++++ 1 file changed, 595 insertions(+) diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c index 0469c783f4fa..ea9b5815e828 100644 --- a/tools/testing/selftests/mm/guard-regions.c +++ b/tools/testing/selftests/mm/guard-regions.c @@ -216,6 +216,58 @@ static int open_file(const char *prefix, char *path) return fd; } +/* Establish a varying pattern in a buffer. */ +static void set_pattern(char *ptr, size_t num_pages, size_t page_size) +{ + size_t i; + + for (i = 0; i < num_pages; i++) { + char *ptr2 = &ptr[i * page_size]; + + memset(ptr2, 'a' + (i % 26), page_size); + } +} + +/* + * Check that a buffer contains the pattern set by set_pattern(), starting at a + * page offset of pgoff within the buffer. + */ +static bool check_pattern_offset(char *ptr, size_t num_pages, size_t page_size, + size_t pgoff) +{ + size_t i; + + for (i = 0; i < num_pages * page_size; i++) { + size_t offset = pgoff * page_size + i; + char actual = ptr[offset]; + char expected = 'a' + ((offset / page_size) % 26); + + if (actual != expected) + return false; + } + + return true; +} + +/* Check that a buffer contains the pattern set by set_pattern(). */ +static bool check_pattern(char *ptr, size_t num_pages, size_t page_size) +{ + return check_pattern_offset(ptr, num_pages, page_size, 0); +} + +/* Determine if a buffer contains only repetitions of a specified char. */ +static bool is_buf_eq(char *buf, size_t size, char chr) +{ + size_t i; + + for (i = 0; i < size; i++) { + if (buf[i] != chr) + return false; + } + + return true; +} + FIXTURE_SETUP(guard_regions) { self->page_size = (unsigned long)sysconf(_SC_PAGESIZE); @@ -1437,4 +1489,547 @@ TEST_F(guard_regions, uffd) ASSERT_EQ(munmap(ptr, 10 * page_size), 0); } +/* + * Mark a region within a file-backed mapping using MADV_SEQUENTIAL so we + * aggressively read-ahead, then install guard regions and assert that it + * behaves correctly. + * + * We page out using MADV_PAGEOUT before checking guard regions so we drop page + * cache folios, meaning we maximise the possibility of some broken readahead. + */ +TEST_F(guard_regions, madvise_sequential) +{ + char *ptr; + int i; + const unsigned long page_size = self->page_size; + + if (variant->backing == ANON_BACKED) + SKIP(return, "MADV_SEQUENTIAL meaningful only for file-backed"); + + ptr = mmap_(self, variant, NULL, 10 * page_size, + PROT_READ | PROT_WRITE, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Establish a pattern of data in the file. */ + set_pattern(ptr, 10, page_size); + ASSERT_TRUE(check_pattern(ptr, 10, page_size)); + + /* Mark it as being accessed sequentially. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_SEQUENTIAL), 0); + + /* Mark every other page a guard page. */ + for (i = 0; i < 10; i += 2) { + char *ptr2 = &ptr[i * page_size]; + + ASSERT_EQ(madvise(ptr2, page_size, MADV_GUARD_INSTALL), 0); + } + + /* Now page it out. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_PAGEOUT), 0); + + /* Now make sure pages are as expected. */ + for (i = 0; i < 10; i++) { + char *chrp = &ptr[i * page_size]; + + if (i % 2 == 0) { + bool result = try_read_write_buf(chrp); + + ASSERT_FALSE(result); + } else { + ASSERT_EQ(*chrp, 'a' + i); + } + } + + /* Now remove guard pages. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0); + + /* Now make sure all data is as expected. */ + if (!check_pattern(ptr, 10, page_size)) + ASSERT_TRUE(false); + + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* + * Check that file-backed mappings implement guard regions with MAP_PRIVATE + * correctly. + */ +TEST_F(guard_regions, map_private) +{ + const unsigned long page_size = self->page_size; + char *ptr_shared, *ptr_private; + int i; + + if (variant->backing == ANON_BACKED) + SKIP(return, "MAP_PRIVATE test specific to file-backed"); + + ptr_shared = mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PROT_WRITE, 0, 0); + ASSERT_NE(ptr_shared, MAP_FAILED); + + /* Manually mmap(), do not use mmap_() wrapper so we can force MAP_PRIVATE. */ + ptr_private = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, self->fd, 0); + ASSERT_NE(ptr_private, MAP_FAILED); + + /* Set pattern in shared mapping. */ + set_pattern(ptr_shared, 10, page_size); + + /* Install guard regions in every other page in the shared mapping. */ + for (i = 0; i < 10; i += 2) { + char *ptr = &ptr_shared[i * page_size]; + + ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_INSTALL), 0); + } + + for (i = 0; i < 10; i++) { + /* Every even shared page should be guarded. */ + ASSERT_EQ(try_read_buf(&ptr_shared[i * page_size]), i % 2 != 0); + /* Private mappings should always be readable. */ + ASSERT_TRUE(try_read_buf(&ptr_private[i * page_size])); + } + + /* Install guard regions in every other page in the private mapping. */ + for (i = 0; i < 10; i += 2) { + char *ptr = &ptr_private[i * page_size]; + + ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_INSTALL), 0); + } + + for (i = 0; i < 10; i++) { + /* Every even shared page should be guarded. */ + ASSERT_EQ(try_read_buf(&ptr_shared[i * page_size]), i % 2 != 0); + /* Every odd private page should be guarded. */ + ASSERT_EQ(try_read_buf(&ptr_private[i * page_size]), i % 2 != 0); + } + + /* Remove guard regions from shared mapping. */ + ASSERT_EQ(madvise(ptr_shared, 10 * page_size, MADV_GUARD_REMOVE), 0); + + for (i = 0; i < 10; i++) { + /* Shared mappings should always be readable. */ + ASSERT_TRUE(try_read_buf(&ptr_shared[i * page_size])); + /* Every even private page should be guarded. */ + ASSERT_EQ(try_read_buf(&ptr_private[i * page_size]), i % 2 != 0); + } + + /* Remove guard regions from private mapping. */ + ASSERT_EQ(madvise(ptr_private, 10 * page_size, MADV_GUARD_REMOVE), 0); + + for (i = 0; i < 10; i++) { + /* Shared mappings should always be readable. */ + ASSERT_TRUE(try_read_buf(&ptr_shared[i * page_size])); + /* Private mappings should always be readable. */ + ASSERT_TRUE(try_read_buf(&ptr_private[i * page_size])); + } + + /* Ensure patterns are intact. */ + ASSERT_TRUE(check_pattern(ptr_shared, 10, page_size)); + ASSERT_TRUE(check_pattern(ptr_private, 10, page_size)); + + /* Now write out every other page to MAP_PRIVATE. */ + for (i = 0; i < 10; i += 2) { + char *ptr = &ptr_private[i * page_size]; + + memset(ptr, 'a' + i, page_size); + } + + /* + * At this point the mapping is: + * + * 0123456789 + * SPSPSPSPSP + * + * Where S = shared, P = private mappings. + */ + + /* Now mark the beginning of the mapping guarded. */ + ASSERT_EQ(madvise(ptr_private, 5 * page_size, MADV_GUARD_INSTALL), 0); + + /* + * This renders the mapping: + * + * 0123456789 + * xxxxxPSPSP + */ + + for (i = 0; i < 10; i++) { + char *ptr = &ptr_private[i * page_size]; + + /* Ensure guard regions as expected. */ + ASSERT_EQ(try_read_buf(ptr), i >= 5); + /* The shared mapping should always succeed. */ + ASSERT_TRUE(try_read_buf(&ptr_shared[i * page_size])); + } + + /* Remove the guard regions altogether. */ + ASSERT_EQ(madvise(ptr_private, 10 * page_size, MADV_GUARD_REMOVE), 0); + + /* + * + * We now expect the mapping to be: + * + * 0123456789 + * SSSSSPSPSP + * + * As we removed guard regions, the private pages from the first 5 will + * have been zapped, so on fault will reestablish the shared mapping. + */ + + for (i = 0; i < 10; i++) { + char *ptr = &ptr_private[i * page_size]; + + /* + * Assert that shared mappings in the MAP_PRIVATE mapping match + * the shared mapping. + */ + if (i < 5 || i % 2 == 0) { + char *ptr_s = &ptr_shared[i * page_size]; + + ASSERT_EQ(memcmp(ptr, ptr_s, page_size), 0); + continue; + } + + /* Everything else is a private mapping. */ + ASSERT_TRUE(is_buf_eq(ptr, page_size, 'a' + i)); + } + + ASSERT_EQ(munmap(ptr_shared, 10 * page_size), 0); + ASSERT_EQ(munmap(ptr_private, 10 * page_size), 0); +} + +/* Test that guard regions established over a read-only mapping function correctly. */ +TEST_F(guard_regions, readonly_file) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + if (variant->backing == ANON_BACKED) + SKIP(return, "Read-only test specific to file-backed"); + + /* Map shared so we can populate with pattern, populate it, unmap. */ + ptr = mmap_(self, variant, NULL, 10 * page_size, + PROT_READ | PROT_WRITE, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + set_pattern(ptr, 10, page_size); + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); + /* Close the fd so we can re-open read-only. */ + ASSERT_EQ(close(self->fd), 0); + + /* Re-open read-only. */ + self->fd = open(self->path, O_RDONLY); + ASSERT_NE(self->fd, -1); + /* Re-map read-only. */ + ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Mark every other page guarded. */ + for (i = 0; i < 10; i += 2) { + char *ptr_pg = &ptr[i * page_size]; + + ASSERT_EQ(madvise(ptr_pg, page_size, MADV_GUARD_INSTALL), 0); + } + + /* Assert that the guard regions are in place.*/ + for (i = 0; i < 10; i++) { + char *ptr_pg = &ptr[i * page_size]; + + ASSERT_EQ(try_read_buf(ptr_pg), i % 2 != 0); + } + + /* Remove guard regions. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0); + + /* Ensure the data is as expected. */ + ASSERT_TRUE(check_pattern(ptr, 10, page_size)); + + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +TEST_F(guard_regions, fault_around) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + if (variant->backing == ANON_BACKED) + SKIP(return, "Fault-around test specific to file-backed"); + + ptr = mmap_(self, variant, NULL, 10 * page_size, + PROT_READ | PROT_WRITE, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Establish a pattern in the backing file. */ + set_pattern(ptr, 10, page_size); + + /* + * Now drop it from the page cache so we get major faults when next we + * map it. + */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_PAGEOUT), 0); + + /* Unmap and remap 'to be sure'. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); + ptr = mmap_(self, variant, NULL, 10 * page_size, + PROT_READ | PROT_WRITE, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Now make every even page guarded. */ + for (i = 0; i < 10; i += 2) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(madvise(ptr_p, page_size, MADV_GUARD_INSTALL), 0); + } + + /* Now fault in every odd page. This should trigger fault-around. */ + for (i = 1; i < 10; i += 2) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_TRUE(try_read_buf(ptr_p)); + } + + /* Finally, ensure that guard regions are intact as expected. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(try_read_buf(ptr_p), i % 2 != 0); + } + + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +TEST_F(guard_regions, truncation) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + if (variant->backing == ANON_BACKED) + SKIP(return, "Truncation test specific to file-backed"); + + ptr = mmap_(self, variant, NULL, 10 * page_size, + PROT_READ | PROT_WRITE, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* + * Establish a pattern in the backing file, just so there is data + * there. + */ + set_pattern(ptr, 10, page_size); + + /* Now make every even page guarded. */ + for (i = 0; i < 10; i += 2) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(madvise(ptr_p, page_size, MADV_GUARD_INSTALL), 0); + } + + /* Now assert things are as expected. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(try_read_write_buf(ptr_p), i % 2 != 0); + } + + /* Now truncate to actually used size (initialised to 100). */ + ASSERT_EQ(ftruncate(self->fd, 10 * page_size), 0); + + /* Here the guard regions will remain intact. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(try_read_write_buf(ptr_p), i % 2 != 0); + } + + /* Now truncate to half the size, then truncate again to the full size. */ + ASSERT_EQ(ftruncate(self->fd, 5 * page_size), 0); + ASSERT_EQ(ftruncate(self->fd, 10 * page_size), 0); + + /* Again, guard pages will remain intact. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(try_read_write_buf(ptr_p), i % 2 != 0); + } + + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +TEST_F(guard_regions, hole_punch) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + if (variant->backing == ANON_BACKED) + SKIP(return, "Truncation test specific to file-backed"); + + /* Establish pattern in mapping. */ + ptr = mmap_(self, variant, NULL, 10 * page_size, + PROT_READ | PROT_WRITE, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + set_pattern(ptr, 10, page_size); + + /* Install a guard region in the middle of the mapping. */ + ASSERT_EQ(madvise(&ptr[3 * page_size], 4 * page_size, + MADV_GUARD_INSTALL), 0); + + /* + * The buffer will now be: + * + * 0123456789 + * ***xxxx*** + * + * Where * is data and x is the guard region. + */ + + /* Ensure established. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(try_read_buf(ptr_p), i < 3 || i >= 7); + } + + /* Now hole punch the guarded region. */ + ASSERT_EQ(madvise(&ptr[3 * page_size], 4 * page_size, + MADV_REMOVE), 0); + + /* Ensure guard regions remain. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(try_read_buf(ptr_p), i < 3 || i >= 7); + } + + /* Now remove guard region throughout. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0); + + /* Check that the pattern exists in non-hole punched region. */ + ASSERT_TRUE(check_pattern(ptr, 3, page_size)); + /* Check that hole punched region is zeroed. */ + ASSERT_TRUE(is_buf_eq(&ptr[3 * page_size], 4 * page_size, '\0')); + /* Check that the pattern exists in the remainder of the file. */ + ASSERT_TRUE(check_pattern_offset(ptr, 3, page_size, 7)); + + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* + * Ensure that a memfd works correctly with guard regions, that we can write + * seal it then open the mapping read-only and still establish guard regions + * within, remove those guard regions and have everything work correctly. + */ +TEST_F(guard_regions, memfd_write_seal) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + if (variant->backing != SHMEM_BACKED) + SKIP(return, "memfd write seal test specific to shmem"); + + /* OK, we need a memfd, so close existing one. */ + ASSERT_EQ(close(self->fd), 0); + + /* Create and truncate memfd. */ + self->fd = memfd_create("guard_regions_memfd_seals_test", + MFD_ALLOW_SEALING); + ASSERT_NE(self->fd, -1); + ASSERT_EQ(ftruncate(self->fd, 10 * page_size), 0); + + /* Map, set pattern, unmap. */ + ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PROT_WRITE, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + set_pattern(ptr, 10, page_size); + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); + + /* Write-seal the memfd. */ + ASSERT_EQ(fcntl(self->fd, F_ADD_SEALS, F_SEAL_WRITE), 0); + + /* Now map the memfd readonly. */ + ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Ensure pattern is as expected. */ + ASSERT_TRUE(check_pattern(ptr, 10, page_size)); + + /* Now make every even page guarded. */ + for (i = 0; i < 10; i += 2) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(madvise(ptr_p, page_size, MADV_GUARD_INSTALL), 0); + } + + /* Now assert things are as expected. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(try_read_buf(ptr_p), i % 2 != 0); + } + + /* Now remove guard regions. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0); + + /* Ensure pattern is as expected. */ + ASSERT_TRUE(check_pattern(ptr, 10, page_size)); + + /* Ensure write seal intact. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_FALSE(try_write_buf(ptr_p)); + } + + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + + +/* + * Since we are now permitted to establish guard regions in read-only anonymous + * mappings, for the sake of thoroughness, though it probably has no practical + * use, test that guard regions function with a mapping to the anonymous zero + * page. + */ +TEST_F(guard_regions, anon_zeropage) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + if (!is_anon_backed(variant)) + SKIP(return, "anon zero page test specific to anon/shmem"); + + /* Obtain a read-only i.e. anon zero page mapping. */ + ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ, 0, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Now make every even page guarded. */ + for (i = 0; i < 10; i += 2) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(madvise(ptr_p, page_size, MADV_GUARD_INSTALL), 0); + } + + /* Now assert things are as expected. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_EQ(try_read_buf(ptr_p), i % 2 != 0); + } + + /* Now remove all guard regions. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0); + + /* Now assert things are as expected. */ + for (i = 0; i < 10; i++) { + char *ptr_p = &ptr[i * page_size]; + + ASSERT_TRUE(try_read_buf(ptr_p)); + } + + /* Ensure zero page...*/ + ASSERT_TRUE(is_buf_eq(ptr, 10 * page_size, '\0')); + + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + TEST_HARNESS_MAIN