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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, Muchun Song , Richard Henderson , Ivan Kokshaysky , Matt Turner , Thomas Bogendoerfer , "James E . J . Bottomley" , Helge Deller , Chris Zankel , Max Filippov , Arnd Bergmann , linux-alpha@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-arch@vger.kernel.org, Shuah Khan , Christian Brauner , linux-kselftest@vger.kernel.org, Sidhartha Kumar Subject: [RFC PATCH 4/4] selftests/mm: add self tests for guard page feature Date: Fri, 27 Sep 2024 13:51:14 +0100 Message-ID: <7906f1f50cf6e2d734965627625c3a1df8c3e3e9.1727440966.git.lorenzo.stoakes@oracle.com> X-Mailer: git-send-email 2.46.2 In-Reply-To: References: X-ClientProxiedBy: LO4P265CA0067.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:2af::17) To SJ0PR10MB5613.namprd10.prod.outlook.com (2603:10b6:a03:3d0::5) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ0PR10MB5613:EE_|IA0PR10MB6820:EE_ X-MS-Office365-Filtering-Correlation-Id: e9ea31e9-0d1c-4e4e-c431-08dcdef3201b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: 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We start by implement basic tests asserting that guard pages can be established (poisoned), cleared (remedied) and that touching poisoned pages result in SIGSEGV. We also assert that, in remedying a range, non-poison pages remain intact. We then examine different operations on regions containing poison markers behave to ensure correct behaviour: * Operations over multiple VMAs operate as expected. * Invoking MADV_GUARD_POISION / MADV_GUARD_REMEDY via process_madvise() in batches works correctly. * Ensuring that munmap() correctly tears down poison markers. * Using mprotect() to adjust protection bits does not in any way override or cause issues with poison markers. * Ensuring that splitting and merging VMAs around poison markers causes no issue - i.e. that a marker which 'belongs' to one VMA can function just as well 'belonging' to another. * Ensuring that madvise(..., MADV_DONTNEED) does not remove poison markers. * Ensuring that mlock()'ing a range containing poison markers does not cause issues. * Ensuring that mremap() can move a poisoned range and retain poison markers. * Ensuring that mremap() can expand a poisoned range and retain poison markers (perhaps moving the range). * Ensuring that mremap() can shrink a poisoned range and retain poison markers. * Ensuring that forking a process correctly retains poison markers. * Ensuring that forking a VMA with VM_WIPEONFORK set behaves sanely. * Ensuring that lazyfree simply clears poison markers. * Ensuring that userfaultfd can co-exist with guard pages. * Ensuring that madvise(..., MADV_POPULATE_READ) and madvise(..., MADV_POPULATE_WRITE) error out when encountering poison markers. * Ensuring that madvise(..., MADV_COLD) and madvise(..., MADV_PAGEOUT) do not remove poison markers. Signed-off-by: Lorenzo Stoakes --- tools/testing/selftests/mm/.gitignore | 1 + tools/testing/selftests/mm/Makefile | 1 + tools/testing/selftests/mm/guard-pages.c | 1168 ++++++++++++++++++++++ 3 files changed, 1170 insertions(+) create mode 100644 tools/testing/selftests/mm/guard-pages.c diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore index 689bbd520296..8f01f4da1c0d 100644 --- a/tools/testing/selftests/mm/.gitignore +++ b/tools/testing/selftests/mm/.gitignore @@ -54,3 +54,4 @@ droppable hugetlb_dio pkey_sighandler_tests_32 pkey_sighandler_tests_64 +guard-pages diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile index 02e1204971b0..15c734d6cfec 100644 --- a/tools/testing/selftests/mm/Makefile +++ b/tools/testing/selftests/mm/Makefile @@ -79,6 +79,7 @@ TEST_GEN_FILES += hugetlb_fault_after_madv TEST_GEN_FILES += hugetlb_madv_vs_map TEST_GEN_FILES += hugetlb_dio TEST_GEN_FILES += droppable +TEST_GEN_FILES += guard-pages ifneq ($(ARCH),arm64) TEST_GEN_FILES += soft-dirty diff --git a/tools/testing/selftests/mm/guard-pages.c b/tools/testing/selftests/mm/guard-pages.c new file mode 100644 index 000000000000..2ab0ff3ba5a0 --- /dev/null +++ b/tools/testing/selftests/mm/guard-pages.c @@ -0,0 +1,1168 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +#define _GNU_SOURCE +#include "../kselftest_harness.h" +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* These may not yet be available in the uAPI so define if not. */ + +#ifndef MADV_GUARD_POISON +#define MADV_GUARD_POISON 102 +#endif + +#ifndef MADV_GUARD_UNPOISON +#define MADV_GUARD_UNPOISON 103 +#endif + +volatile bool signal_jump_set; +sigjmp_buf signal_jmp_buf; + +static int userfaultfd(int flags) +{ + return syscall(SYS_userfaultfd, flags); +} + +static void handle_fatal(int c) +{ + if (!signal_jump_set) + return; + + siglongjmp(signal_jmp_buf, c); +} + +static int pidfd_open(pid_t pid, unsigned int flags) +{ + return syscall(SYS_pidfd_open, pid, flags); +} + +/* + * Enable our signal catcher and try to read/write the specified buffer. The + * return value indicates whether the read/write succeeds without a fatal + * signal. + */ +static bool try_access_buf(char *ptr, bool write) +{ + bool failed; + + /* Tell signal handler to jump back here on fatal signal. */ + signal_jump_set = true; + /* If a fatal signal arose, we will jump back here and failed is set. */ + failed = sigsetjmp(signal_jmp_buf, 0) != 0; + + if (!failed) { + if (write) { + *ptr = 'x'; + } else { + const volatile char *chr = ptr; + + /* Force read. */ + (void)*chr; + } + } + + signal_jump_set = false; + return !failed; +} + +/* Try and read from a buffer, return true if no fatal signal. */ +static bool try_read_buf(char *ptr) +{ + return try_access_buf(ptr, false); +} + +/* Try and write to a buffer, return true if no fatal signal. */ +static bool try_write_buf(char *ptr) +{ + return try_access_buf(ptr, true); +} + +/* + * Try and BOTH read from AND write to a buffer, return true if BOTH operations + * succeed. + */ +static bool try_read_write_buf(char *ptr) +{ + return try_read_buf(ptr) && try_write_buf(ptr); +} + +FIXTURE(guard_pages) +{ + unsigned long page_size; +}; + +FIXTURE_SETUP(guard_pages) +{ + struct sigaction act = { + .sa_handler = &handle_fatal, + .sa_flags = SA_NODEFER, + }; + + sigemptyset(&act.sa_mask); + if (sigaction(SIGSEGV, &act, NULL)) { + perror("sigaction"); + ksft_exit_fail(); + } + + self->page_size = (unsigned long)sysconf(_SC_PAGESIZE); +}; + +FIXTURE_TEARDOWN(guard_pages) +{ + struct sigaction act = { + .sa_handler = SIG_DFL, + .sa_flags = SA_NODEFER, + }; + + sigemptyset(&act.sa_mask); + sigaction(SIGSEGV, &act, NULL); +} + +TEST_F(guard_pages, basic) +{ + const unsigned long NUM_PAGES = 10; + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + ptr = mmap(NULL, NUM_PAGES * page_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANON, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Trivially assert we can touch the first page. */ + ASSERT_TRUE(try_read_write_buf(ptr)); + + ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_POISON), 0); + + /* Establish that 1st page SIGSEGV's. */ + ASSERT_FALSE(try_read_write_buf(ptr)); + + /* Ensure we can touch everything else.*/ + for (i = 1; i < NUM_PAGES; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Establish a guard page at the end of the mapping. */ + ASSERT_EQ(madvise(&ptr[(NUM_PAGES - 1) * page_size], page_size, + MADV_GUARD_POISON), 0); + + /* Check that both guard pages result in SIGSEGV. */ + ASSERT_FALSE(try_read_write_buf(ptr)); + ASSERT_FALSE(try_read_write_buf(&ptr[(NUM_PAGES - 1) * page_size])); + + /* Unpoison the first. */ + ASSERT_FALSE(madvise(ptr, page_size, MADV_GUARD_UNPOISON)); + + /* Make sure we can touch it. */ + ASSERT_TRUE(try_read_write_buf(ptr)); + + /* Unpoison the last. */ + ASSERT_FALSE(madvise(&ptr[(NUM_PAGES - 1) * page_size], page_size, + MADV_GUARD_UNPOISON)); + + /* Make sure we can touch it. */ + ASSERT_TRUE(try_read_write_buf(&ptr[(NUM_PAGES - 1) * page_size])); + + /* + * Test setting a _range_ of pages, namely the first 3. The first of + * these be faulted in, so this also tests that we can poison backed + * pages. + */ + ASSERT_EQ(madvise(ptr, 3 * page_size, MADV_GUARD_POISON), 0); + + /* Make sure they are all poisoned. */ + for (i = 0; i < 3; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Make sure the rest are not. */ + for (i = 3; i < NUM_PAGES; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Unpoison them. */ + ASSERT_EQ(madvise(ptr, NUM_PAGES * page_size, MADV_GUARD_UNPOISON), 0); + + /* Now make sure we can touch everything. */ + for (i = 0; i < NUM_PAGES; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Now unpoison everything, make sure we don't remove existing entries */ + ASSERT_EQ(madvise(ptr, NUM_PAGES * page_size, MADV_GUARD_UNPOISON), 0); + + for (i = 0; i < NUM_PAGES * page_size; i += page_size) { + ASSERT_EQ(ptr[i], 'x'); + } + + ASSERT_EQ(munmap(ptr, NUM_PAGES * page_size), 0); +} + +/* Assert that operations applied across multiple VMAs work as expected. */ +TEST_F(guard_pages, multi_vma) +{ + const unsigned long page_size = self->page_size; + char *ptr_region, *ptr, *ptr1, *ptr2, *ptr3; + int i; + + /* Reserve a 100 page region over which we can install VMAs. */ + ptr_region = mmap(NULL, 100 * page_size, PROT_NONE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr_region, MAP_FAILED); + + /* Place a VMA of 10 pages size at the start of the region. */ + ptr1 = mmap(ptr_region, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr1, MAP_FAILED); + + /* Place a VMA of 5 pages size 50 pages into the region. */ + ptr2 = mmap(&ptr_region[50 * page_size], 5 * page_size, + PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr2, MAP_FAILED); + + /* Place a VMA of 20 pages size at the end of the region. */ + ptr3 = mmap(&ptr_region[80 * page_size], 20 * page_size, + PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr3, MAP_FAILED); + + /* Unmap gaps. */ + ASSERT_EQ(munmap(&ptr_region[10 * page_size], 40 * page_size), 0); + ASSERT_EQ(munmap(&ptr_region[55 * page_size], 25 * page_size), 0); + + /* + * We end up with VMAs like this: + * + * 0 10 .. 50 55 .. 80 100 + * [---] [---] [---] + */ + + /* Now poison the whole range and make sure all VMAs are poisoned. */ + + /* + * madvise() is certifiable and lets you perform operations over gaps, + * everything works, but it indicates an error and errno is set to + * -ENOMEM. Also if anything runs out of memory it is set to + * -ENOMEM. You are meant to guess which is which. + */ + ASSERT_EQ(madvise(ptr_region, 100 * page_size, MADV_GUARD_POISON), -1); + ASSERT_EQ(errno, ENOMEM); + + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr1[i * page_size])); + } + + for (i = 0; i < 5; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr2[i * page_size])); + } + + for (i = 0; i < 20; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr3[i * page_size])); + } + + /* Now unpoison the range and assert the opposite. */ + + ASSERT_EQ(madvise(ptr_region, 100 * page_size, MADV_GUARD_UNPOISON), -1); + ASSERT_EQ(errno, ENOMEM); + + for (i = 0; i < 10; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr1[i * page_size])); + } + + for (i = 0; i < 5; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr2[i * page_size])); + } + + for (i = 0; i < 20; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr3[i * page_size])); + } + + /* Now map incompatible VMAs in the gaps. */ + ptr = mmap(&ptr_region[10 * page_size], 40 * page_size, + PROT_READ | PROT_WRITE | PROT_EXEC, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + ptr = mmap(&ptr_region[55 * page_size], 25 * page_size, + PROT_READ | PROT_WRITE | PROT_EXEC, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* + * We end up with VMAs like this: + * + * 0 10 .. 50 55 .. 80 100 + * [---][xxxx][---][xxxx][---] + * + * Where 'x' signifies VMAs that cannot be merged with those adjacent to + * them. + */ + + /* Multiple VMAs adjacent to one another should result in no error. */ + ASSERT_EQ(madvise(ptr_region, 100 * page_size, MADV_GUARD_POISON), 0); + for (i = 0; i < 100; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr_region[i * page_size])); + } + ASSERT_EQ(madvise(ptr_region, 100 * page_size, MADV_GUARD_UNPOISON), 0); + for (i = 0; i < 100; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr_region[i * page_size])); + } + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr_region, 100 * page_size), 0); +} + +/* + * Assert that batched operations performed using process_madvise() work as + * expected. + */ +TEST_F(guard_pages, process_madvise) +{ + const unsigned long page_size = self->page_size; + pid_t pid = getpid(); + int pidfd = pidfd_open(pid, 0); + char *ptr_region, *ptr1, *ptr2, *ptr3; + ssize_t count; + struct iovec vec[6]; + + ASSERT_NE(pidfd, -1); + + /* Reserve region to map over. */ + ptr_region = mmap(NULL, 100 * page_size, PROT_NONE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr_region, MAP_FAILED); + + /* 10 pages offset 1 page into reserve region. */ + ptr1 = mmap(&ptr_region[page_size], 10 * page_size, + PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr1, MAP_FAILED); + /* We want poison markers at start/end of each VMA. */ + vec[0].iov_base = ptr1; + vec[0].iov_len = page_size; + vec[1].iov_base = &ptr1[9 * page_size]; + vec[1].iov_len = page_size; + + /* 5 pages offset 50 pages into reserve region. */ + ptr2 = mmap(&ptr_region[50 * page_size], 5 * page_size, + PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr2, MAP_FAILED); + vec[2].iov_base = ptr2; + vec[2].iov_len = page_size; + vec[3].iov_base = &ptr2[4 * page_size]; + vec[3].iov_len = page_size; + + /* 20 pages offset 79 pages into reserve region. */ + ptr3 = mmap(&ptr_region[79 * page_size], 20 * page_size, + PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr3, MAP_FAILED); + vec[4].iov_base = ptr3; + vec[4].iov_len = page_size; + vec[5].iov_base = &ptr3[19 * page_size]; + vec[5].iov_len = page_size; + + /* Free surrounding VMAs. */ + ASSERT_EQ(munmap(ptr_region, page_size), 0); + ASSERT_EQ(munmap(&ptr_region[11 * page_size], 39 * page_size), 0); + ASSERT_EQ(munmap(&ptr_region[55 * page_size], 24 * page_size), 0); + ASSERT_EQ(munmap(&ptr_region[99 * page_size], page_size), 0); + + /* Now poison in one step. */ + count = process_madvise(pidfd, vec, 6, MADV_GUARD_POISON, 0); + + /* OK we don't have permission to do this, skip. */ + if (count == -1 && errno == EPERM) + ksft_exit_skip("No process_madvise() permissions\n"); + + /* Returns the number of bytes advised. */ + ASSERT_EQ(count, 6 * page_size); + + /* Now make sure the poisoning was applied. */ + + ASSERT_FALSE(try_read_write_buf(ptr1)); + ASSERT_FALSE(try_read_write_buf(&ptr1[9 * page_size])); + + ASSERT_FALSE(try_read_write_buf(ptr2)); + ASSERT_FALSE(try_read_write_buf(&ptr2[4 * page_size])); + + ASSERT_FALSE(try_read_write_buf(ptr3)); + ASSERT_FALSE(try_read_write_buf(&ptr3[19 * page_size])); + + /* Now do the same with unpoison... */ + count = process_madvise(pidfd, vec, 6, MADV_GUARD_UNPOISON, 0); + + /* ...and everything should now succeed. */ + + ASSERT_TRUE(try_read_write_buf(ptr1)); + ASSERT_TRUE(try_read_write_buf(&ptr1[9 * page_size])); + + ASSERT_TRUE(try_read_write_buf(ptr2)); + ASSERT_TRUE(try_read_write_buf(&ptr2[4 * page_size])); + + ASSERT_TRUE(try_read_write_buf(ptr3)); + ASSERT_TRUE(try_read_write_buf(&ptr3[19 * page_size])); + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr1, 10 * page_size), 0); + ASSERT_EQ(munmap(ptr2, 5 * page_size), 0); + ASSERT_EQ(munmap(ptr3, 20 * page_size), 0); + close(pidfd); +} + +/* Assert that unmapping ranges does not leave poison behind. */ +TEST_F(guard_pages, munmap) +{ + const unsigned long page_size = self->page_size; + char *ptr, *ptr_new1, *ptr_new2; + + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Poison first and last pages. */ + ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_POISON), 0); + ASSERT_EQ(madvise(&ptr[9 * page_size], page_size, MADV_GUARD_POISON), 0); + + /* Assert that they are poisoned. */ + ASSERT_FALSE(try_read_write_buf(ptr)); + ASSERT_FALSE(try_read_write_buf(&ptr[9 * page_size])); + + /* Unmap them. */ + ASSERT_EQ(munmap(ptr, page_size), 0); + ASSERT_EQ(munmap(&ptr[9 * page_size], page_size), 0); + + /* Map over them.*/ + ptr_new1 = mmap(ptr, page_size, PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr_new1, MAP_FAILED); + ptr_new2 = mmap(&ptr[9 * page_size], page_size, PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr_new2, MAP_FAILED); + + /* Assert that they are now not poisoned. */ + ASSERT_TRUE(try_read_write_buf(ptr_new1)); + ASSERT_TRUE(try_read_write_buf(ptr_new2)); + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* Assert that mprotect() operations have no bearing on guard poison markers. */ +TEST_F(guard_pages, mprotect) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Poison the middle of the range. */ + ASSERT_EQ(madvise(&ptr[5 * page_size], 2 * page_size, + MADV_GUARD_POISON), 0); + + /* Assert that it is indeed poisoned. */ + ASSERT_FALSE(try_read_write_buf(&ptr[5 * page_size])); + ASSERT_FALSE(try_read_write_buf(&ptr[6 * page_size])); + + /* Now make these pages read-only. */ + ASSERT_EQ(mprotect(&ptr[5 * page_size], 2 * page_size, PROT_READ), 0); + + /* Make sure the range is still poisoned. */ + ASSERT_FALSE(try_read_buf(&ptr[5 * page_size])); + ASSERT_FALSE(try_read_buf(&ptr[6 * page_size])); + + /* Make sure we can poison again without issue.*/ + ASSERT_EQ(madvise(&ptr[5 * page_size], 2 * page_size, + MADV_GUARD_POISON), 0); + + /* Make sure the range is, yet again, still poisoned. */ + ASSERT_FALSE(try_read_buf(&ptr[5 * page_size])); + ASSERT_FALSE(try_read_buf(&ptr[6 * page_size])); + + /* Now unpoison the whole range. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_UNPOISON), 0); + + /* Make sure the whole range is readable. */ + for (i = 0; i < 10; i++) { + ASSERT_TRUE(try_read_buf(&ptr[i * page_size])); + } + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* Split and merge VMAs and make sure guard pages still behave. */ +TEST_F(guard_pages, split_merge) +{ + const unsigned long page_size = self->page_size; + char *ptr, *ptr_new; + int i; + + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Poison the whole range. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_POISON), 0); + + /* Make sure the whole range is poisoned. */ + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Now unmap some pages in the range so we split. */ + ASSERT_EQ(munmap(&ptr[2 * page_size], page_size), 0); + ASSERT_EQ(munmap(&ptr[5 * page_size], page_size), 0); + ASSERT_EQ(munmap(&ptr[8 * page_size], page_size), 0); + + /* Make sure the remaining ranges are poisoned post-split. */ + for (i = 0; i < 2; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + for (i = 2; i < 5; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + for (i = 6; i < 8; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + for (i = 9; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Now map them again - the unmap will have cleared the poison. */ + ptr_new = mmap(&ptr[2 * page_size], page_size, PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr_new, MAP_FAILED); + ptr_new = mmap(&ptr[5 * page_size], page_size, PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr_new, MAP_FAILED); + ptr_new = mmap(&ptr[8 * page_size], page_size, PROT_READ | PROT_WRITE, + MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr_new, MAP_FAILED); + + /* Now make sure poisoning is as expected. */ + for (i = 0; i < 10; i++) { + bool result = try_read_write_buf(&ptr[i * page_size]); + + if (i == 2 || i == 5 || i == 8) { + ASSERT_TRUE(result); + } else { + ASSERT_FALSE(result); + } + } + + /* Now poison everything again. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_POISON), 0); + + /* Make sure the whole range is poisoned. */ + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Now split the range into three. */ + ASSERT_EQ(mprotect(ptr, 3 * page_size, PROT_READ), 0); + ASSERT_EQ(mprotect(&ptr[7 * page_size], 3 * page_size, PROT_READ), 0); + + /* Make sure the whole range is poisoned for read. */ + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_buf(&ptr[i * page_size])); + } + + /* Now reset protection bits so we merge the whole thing. */ + ASSERT_EQ(mprotect(ptr, 3 * page_size, PROT_READ | PROT_WRITE), 0); + ASSERT_EQ(mprotect(&ptr[7 * page_size], 3 * page_size, + PROT_READ | PROT_WRITE), 0); + + /* Make sure the whole range is still poisoned. */ + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Split range into 3 again... */ + ASSERT_EQ(mprotect(ptr, 3 * page_size, PROT_READ), 0); + ASSERT_EQ(mprotect(&ptr[7 * page_size], 3 * page_size, PROT_READ), 0); + + /* ...and unpoison the whole range. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_UNPOISON), 0); + + /* Make sure the whole range is remedied for read. */ + for (i = 0; i < 10; i++) { + ASSERT_TRUE(try_read_buf(&ptr[i * page_size])); + } + + /* Merge them again. */ + ASSERT_EQ(mprotect(ptr, 3 * page_size, PROT_READ | PROT_WRITE), 0); + ASSERT_EQ(mprotect(&ptr[7 * page_size], 3 * page_size, + PROT_READ | PROT_WRITE), 0); + + /* Now ensure the merged range is remedied for read/write. */ + for (i = 0; i < 10; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* Assert that MADV_DONTNEED does not remove guard poison markers. */ +TEST_F(guard_pages, dontneed) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Back the whole range. */ + for (i = 0; i < 10; i++) { + ptr[i * page_size] = 'y'; + } + + /* Poison every other page. */ + for (i = 0; i < 10; i += 2) { + ASSERT_EQ(madvise(&ptr[i * page_size], + page_size, MADV_GUARD_POISON), 0); + } + + /* Indicate that we don't need any of the range. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_DONTNEED), 0); + + /* Check to ensure poison markers are still in place. */ + for (i = 0; i < 10; i++) { + bool result = try_read_buf(&ptr[i * page_size]); + + if (i % 2 == 0) { + ASSERT_FALSE(result); + } else { + ASSERT_TRUE(result); + /* Make sure we really did get reset to zero page. */ + ASSERT_EQ(ptr[i * page_size], '\0'); + } + + /* Now write... */ + result = try_write_buf(&ptr[i * page_size]); + + /* ...and make sure same result. */ + if (i % 2 == 0) { + ASSERT_FALSE(result); + } else { + ASSERT_TRUE(result); + } + } + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* Assert that mlock()'ed pages work correctly with poison markers. */ +TEST_F(guard_pages, mlock) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Populate. */ + for (i = 0; i < 10; i++) { + ptr[i * page_size] = 'y'; + } + + /* Lock. */ + ASSERT_EQ(mlock(ptr, 10 * page_size), 0); + + /* Now try to poison, should fail with EINVAL. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_POISON), -1); + ASSERT_EQ(errno, EINVAL); + + /* OK unlock. */ + ASSERT_EQ(munlock(ptr, 10 * page_size), 0); + + /* Poison first half of range, should now succeed. */ + ASSERT_EQ(madvise(ptr, 5 * page_size, MADV_GUARD_POISON), 0); + + /* Make sure poison works. */ + for (i = 0; i < 10; i++) { + bool result = try_read_write_buf(&ptr[i * page_size]); + + if (i < 5) { + ASSERT_FALSE(result); + } else { + ASSERT_TRUE(result); + ASSERT_EQ(ptr[i * page_size], 'x'); + } + } + + /* + * Now lock the latter part of the range. We can't lock the poisoned + * pages, as this would result in the pages being populated and the + * poisoning would cause this to error out. + */ + ASSERT_EQ(mlock(&ptr[5 * page_size], 5 * page_size), 0); + + /* + * Now unpoison, we do not permit mlock()'d ranges to be remedied as it is + * a non-destructive operation. + */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_UNPOISON), 0); + + /* Now check that everything is remedied. */ + for (i = 0; i < 10; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* + * Assert that moving, extending and shrinking memory via mremap() retains + * poison markers where possible. + * + * - Moving a mapping alone should retain markers as they are. + */ +TEST_F(guard_pages, mremap_move) +{ + const unsigned long page_size = self->page_size; + char *ptr, *ptr_new; + + /* Map 5 pages. */ + ptr = mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Place poison markers at both ends of the 5 page span. */ + ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_POISON), 0); + ASSERT_EQ(madvise(&ptr[4 * page_size], page_size, MADV_GUARD_POISON), 0); + + /* Make sure the poison is in effect. */ + ASSERT_FALSE(try_read_write_buf(ptr)); + ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size])); + + /* Map a new region we will move this range into. Doing this ensures + * that we have reserved a range to map into. + */ + ptr_new = mmap(NULL, 5 * page_size, PROT_NONE, MAP_ANON | MAP_PRIVATE, + -1, 0); + ASSERT_NE(ptr_new, MAP_FAILED); + + ASSERT_EQ(mremap(ptr, 5 * page_size, 5 * page_size, + MREMAP_MAYMOVE | MREMAP_FIXED, ptr_new), ptr_new); + + /* Make sure the poison is retained. */ + ASSERT_FALSE(try_read_write_buf(ptr_new)); + ASSERT_FALSE(try_read_write_buf(&ptr_new[4 * page_size])); + + /* + * Clean up - we only need reference the new pointer as we overwrote the + * PROT_NONE range and moved the existing one. + */ + munmap(ptr_new, 5 * page_size); +} + +/* + * Assert that moving, extending and shrinking memory via mremap() retains + * poison markers where possible. + * + * - Expanding should retain, only now in different position. The user will have + * to unpoison manually to fix up (they'd have to do the same if it were a + * PROT_NONE mapping) + */ +TEST_F(guard_pages, mremap_expand) +{ + const unsigned long page_size = self->page_size; + char *ptr, *ptr_new; + + /* Map 10 pages... */ + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + /* ...But unmap the last 5 so we can ensure we can expand into them. */ + ASSERT_EQ(munmap(&ptr[5 * page_size], 5 * page_size), 0); + + /* Place poison markers at both ends of the 5 page span. */ + ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_POISON), 0); + ASSERT_EQ(madvise(&ptr[4 * page_size], page_size, MADV_GUARD_POISON), 0); + + /* Make sure the poison is in effect. */ + ASSERT_FALSE(try_read_write_buf(ptr)); + ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size])); + + /* Now expand to 10 pages. */ + ptr = mremap(ptr, 5 * page_size, 10 * page_size, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Make sure the poison is retained in its original positions. */ + ASSERT_FALSE(try_read_write_buf(ptr)); + ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size])); + + /* Reserve a region which we can move to and expand into. */ + ptr_new = mmap(NULL, 20 * page_size, PROT_NONE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr_new, MAP_FAILED); + + /* Now move and expand into it. */ + ptr = mremap(ptr, 10 * page_size, 20 * page_size, + MREMAP_MAYMOVE | MREMAP_FIXED, ptr_new); + ASSERT_EQ(ptr, ptr_new); + + /* Again, make sure the poison is retained in its original + * positions. */ + ASSERT_FALSE(try_read_write_buf(ptr)); + ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size])); + + /* + * A real user would have to unpoison, but would reasonably expect all + * characteristics of the mapping to be retained, including poison + * markers. + */ + + /* Cleanup. */ + munmap(ptr, 20 * page_size); +} +/* + * Assert that moving, extending and shrinking memory via mremap() retains + * poison markers where possible. + * + * - Shrinking will result in markers that are shrunk over being removed. Again, + * if the user were using a PROT_NONE mapping they'd have to manually fix this + * up also so this is OK. + */ +TEST_F(guard_pages, mremap_shrink) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + /* Map 5 pages. */ + ptr = mmap(NULL, 5 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Place poison markers at both ends of the 5 page span. */ + ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_POISON), 0); + ASSERT_EQ(madvise(&ptr[4 * page_size], page_size, MADV_GUARD_POISON), 0); + + /* Make sure the poison is in effect. */ + ASSERT_FALSE(try_read_write_buf(ptr)); + ASSERT_FALSE(try_read_write_buf(&ptr[4 * page_size])); + + /* Now shrink to 3 pages. */ + ptr = mremap(ptr, 5 * page_size, 3 * page_size, MREMAP_MAYMOVE); + ASSERT_NE(ptr, MAP_FAILED); + + /* We expect the poison marker at the start to be retained... */ + ASSERT_FALSE(try_read_write_buf(ptr)); + + /* ...But remaining pages will not have poison markers. */ + for (i = 1; i < 3; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr[i + page_size])); + } + + /* + * As with expansion, a real user would have to unpoison and fixup. But + * you'd have to do similar manual things with PROT_NONE mappings too. + */ + + /* + * If we expand back to the original size, the end marker will, of + * course, no longer be present. + */ + ptr = mremap(ptr, 3 * page_size, 5 * page_size, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Again, we expect the poison marker at the start to be retained... */ + ASSERT_FALSE(try_read_write_buf(ptr)); + + /* ...But remaining pages will not have poison markers. */ + for (i = 1; i < 5; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr[i + page_size])); + } + + /* Cleanup. */ + munmap(ptr, 5 * page_size); +} + +/* + * Assert that forking a process with VMAs that do not have VM_WIPEONFORK set + * retain guard pages. + */ +TEST_F(guard_pages, fork) +{ + const unsigned long page_size = self->page_size; + char *ptr; + pid_t pid; + int i; + + /* Map 10 pages. */ + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Poison the first 5 pages. */ + ASSERT_EQ(madvise(ptr, 5 * page_size, MADV_GUARD_POISON), 0); + + pid = fork(); + ASSERT_NE(pid, -1); + if (!pid) { + /* This is the child process now. */ + + /* Assert that the poisoning is in effect. */ + for (i = 0; i < 10; i++) { + bool result = try_read_write_buf(&ptr[i * page_size]); + + if (i < 5) { + ASSERT_FALSE(result); + } else { + ASSERT_TRUE(result); + } + } + + /* Now unpoison the range.*/ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_UNPOISON), 0); + + exit(0); + } + + /* Parent process. */ + + /* Parent simply waits on child. */ + waitpid(pid, NULL, 0); + + /* Child unpoison does not impact parent page table state. */ + for (i = 0; i < 10; i++) { + bool result = try_read_write_buf(&ptr[i * page_size]); + + if (i < 5) { + ASSERT_FALSE(result); + } else { + ASSERT_TRUE(result); + } + } + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* + * Assert that forking a process with VMAs that do have VM_WIPEONFORK set + * behave as expected. + */ +TEST_F(guard_pages, fork_wipeonfork) +{ + const unsigned long page_size = self->page_size; + char *ptr; + pid_t pid; + int i; + + /* Map 10 pages. */ + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Mark wipe on fork. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_WIPEONFORK), 0); + + /* Poison the first 5 pages. */ + ASSERT_EQ(madvise(ptr, 5 * page_size, MADV_GUARD_POISON), 0); + + pid = fork(); + ASSERT_NE(pid, -1); + if (!pid) { + /* This is the child process now. */ + + /* Poison will have been wiped. */ + for (i = 0; i < 10; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr[i * page_size])); + } + + exit(0); + } + + /* Parent process. */ + + waitpid(pid, NULL, 0); + + /* Poison should be in effect.*/ + for (i = 0; i < 10; i++) { + bool result = try_read_write_buf(&ptr[i * page_size]); + + if (i < 5) { + ASSERT_FALSE(result); + } else { + ASSERT_TRUE(result); + } + } + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* Ensure that MADV_FREE frees poison entries as expected. */ +TEST_F(guard_pages, lazyfree) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + /* Map 10 pages. */ + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Poison range. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_POISON), 0); + + /* Ensure poisoned. */ + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Lazyfree range. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_FREE), 0); + + /* This should simply clear the poison markers. */ + for (i = 0; i < 10; i++) { + ASSERT_TRUE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* Ensure that MADV_POPULATE_READ, MADV_POPULATE_WRITE behave as expected. */ +TEST_F(guard_pages, populate) +{ + const unsigned long page_size = self->page_size; + char *ptr; + + /* Map 10 pages. */ + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Poison range. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_POISON), 0); + + /* Populate read should error out... */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_POPULATE_READ), -1); + ASSERT_EQ(errno, EFAULT); + + /* ...as should populate write. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_POPULATE_WRITE), -1); + ASSERT_EQ(errno, EFAULT); + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* Ensure that MADV_COLD, MADV_PAGEOUT do not remove poison markers. */ +TEST_F(guard_pages, cold_pageout) +{ + const unsigned long page_size = self->page_size; + char *ptr; + int i; + + /* Map 10 pages. */ + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Poison range. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_POISON), 0); + + /* Ensured poisoned. */ + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Now mark cold. This should have no impact on poison markers. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_COLD), 0); + + /* Should remain poisoned. */ + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* OK, now page out. This should equally, have no effect on markers. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_PAGEOUT), 0); + + /* Should remain poisoned. */ + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Cleanup. */ + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +/* Ensure that guard pages do not break userfaultd. */ +TEST_F(guard_pages, uffd) +{ + const unsigned long page_size = self->page_size; + int uffd; + char *ptr; + int i; + struct uffdio_api api = { + .api = UFFD_API, + .features = 0, + }; + struct uffdio_register reg; + struct uffdio_range range; + + /* Set up uffd. */ + uffd = userfaultfd(0); + if (uffd == -1 && errno == EPERM) + ksft_exit_skip("No uffd permissions\n"); + ASSERT_NE(uffd, -1); + + ASSERT_EQ(ioctl(uffd, UFFDIO_API, &api), 0); + + /* Map 10 pages. */ + ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE, + MAP_ANON | MAP_PRIVATE, -1, 0); + ASSERT_NE(ptr, MAP_FAILED); + + /* Register the range with uffd. */ + range.start = (unsigned long)ptr; + range.len = 10 * page_size; + reg.range = range; + reg.mode = UFFDIO_REGISTER_MODE_MISSING; + ASSERT_EQ(ioctl(uffd, UFFDIO_REGISTER, ®), 0); + + /* Poison the range. This should not trigger the uffd. */ + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_POISON), 0); + + /* The poisoning should behave as usual with no uffd intervention. */ + for (i = 0; i < 10; i++) { + ASSERT_FALSE(try_read_write_buf(&ptr[i * page_size])); + } + + /* Cleanup. */ + ASSERT_EQ(ioctl(uffd, UFFDIO_UNREGISTER, &range), 0); + close(uffd); + ASSERT_EQ(munmap(ptr, 10 * page_size), 0); +} + +TEST_HARNESS_MAIN