[v1,RESEND,2/6] selftests/mm: mkdirty: test behavior of (pte|pmd)_mkdirty on VMAs without write permissions

diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index c31d952cff68..8235dddbbbc6 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -47,6 +47,7 @@  TEST_GEN_FILES += map_hugetlb
 TEST_GEN_FILES += map_populate
 TEST_GEN_FILES += memfd_secret
 TEST_GEN_FILES += migration
+TEST_GEN_PROGS += mkdirty
 TEST_GEN_FILES += mlock-random-test
 TEST_GEN_FILES += mlock2-tests
 TEST_GEN_FILES += mrelease_test
@@ -108,6 +109,7 @@  $(OUTPUT)/cow: vm_util.c
 $(OUTPUT)/khugepaged: vm_util.c
 $(OUTPUT)/ksm_functional_tests: vm_util.c
 $(OUTPUT)/madv_populate: vm_util.c
+$(OUTPUT)/mkdirty: vm_util.c
 $(OUTPUT)/soft-dirty: vm_util.c
 $(OUTPUT)/split_huge_page_test: vm_util.c
 $(OUTPUT)/userfaultfd: vm_util.c
diff --git a/tools/testing/selftests/mm/mkdirty.c b/tools/testing/selftests/mm/mkdirty.c
new file mode 100644
index 000000000000..6d71d972997b
--- /dev/null
+++ b/tools/testing/selftests/mm/mkdirty.c
@@ -0,0 +1,379 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Test handling of code that might set PTE/PMD dirty in read-only VMAs.
+ * Setting a PTE/PMD dirty must not accidentally set the PTE/PMD writable.
+ *
+ * Copyright 2023, Red Hat, Inc.
+ *
+ * Author(s): David Hildenbrand <david@redhat.com>
+ */
+#include <fcntl.h>
+#include <signal.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <sys/mman.h>
+#include <setjmp.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+#include <linux/userfaultfd.h>
+#include <linux/mempolicy.h>
+
+#include "../kselftest.h"
+#include "vm_util.h"
+
+static size_t pagesize;
+static size_t thpsize;
+static int mem_fd;
+static int pagemap_fd;
+static sigjmp_buf env;
+
+static void signal_handler(int sig)
+{
+	if (sig == SIGSEGV)
+		siglongjmp(env, 1);
+	siglongjmp(env, 2);
+}
+
+static void do_test_write_sigsegv(char *mem)
+{
+	char orig = *mem;
+	int ret;
+
+	if (signal(SIGSEGV, signal_handler) == SIG_ERR) {
+		ksft_test_result_fail("signal() failed\n");
+		return;
+	}
+
+	ret = sigsetjmp(env, 1);
+	if (!ret)
+		*mem = orig + 1;
+
+	if (signal(SIGSEGV, SIG_DFL) == SIG_ERR)
+		ksft_test_result_fail("signal() failed\n");
+
+	ksft_test_result(ret == 1 && *mem == orig,
+			 "SIGSEGV generated, page not modified\n");
+}
+
+static char *mmap_thp_range(int prot, char **_mmap_mem, size_t *_mmap_size)
+{
+	const size_t mmap_size = 2 * thpsize;
+	char *mem, *mmap_mem;
+
+	mmap_mem = mmap(NULL, mmap_size, prot, MAP_PRIVATE|MAP_ANON,
+			-1, 0);
+	if (mmap_mem == MAP_FAILED) {
+		ksft_test_result_fail("mmap() failed\n");
+		return MAP_FAILED;
+	}
+	mem = (char *)(((uintptr_t)mmap_mem + thpsize) & ~(thpsize - 1));
+
+	if (madvise(mem, thpsize, MADV_HUGEPAGE)) {
+		ksft_test_result_skip("MADV_HUGEPAGE failed\n");
+		munmap(mmap_mem, mmap_size);
+		return MAP_FAILED;
+	}
+
+	*_mmap_mem = mmap_mem;
+	*_mmap_size = mmap_size;
+	return mem;
+}
+
+static void test_ptrace_write(void)
+{
+	char data = 1;
+	char *mem;
+	int ret;
+
+	ksft_print_msg("[INFO] PTRACE write access\n");
+
+	mem = mmap(NULL, pagesize, PROT_READ, MAP_PRIVATE|MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED) {
+		ksft_test_result_fail("mmap() failed\n");
+		return;
+	}
+
+	/* Fault in the shared zeropage. */
+	if (*mem != 0) {
+		ksft_test_result_fail("Memory not zero\n");
+		goto munmap;
+	}
+
+	/*
+	 * Unshare the page (populating a fresh anon page that might be set
+	 * dirty in the PTE) in the read-only VMA using ptrace (FOLL_FORCE).
+	 */
+	lseek(mem_fd, (uintptr_t) mem, SEEK_SET);
+	ret = write(mem_fd, &data, 1);
+	if (ret != 1 || *mem != data) {
+		ksft_test_result_fail("write() failed\n");
+		goto munmap;
+	}
+
+	do_test_write_sigsegv(mem);
+munmap:
+	munmap(mem, pagesize);
+}
+
+static void test_ptrace_write_thp(void)
+{
+	char *mem, *mmap_mem;
+	size_t mmap_size;
+	char data = 1;
+	int ret;
+
+	ksft_print_msg("[INFO] PTRACE write access to THP\n");
+
+	mem = mmap_thp_range(PROT_READ, &mmap_mem, &mmap_size);
+	if (mem == MAP_FAILED)
+		return;
+
+	/*
+	 * Write to the first subpage in the read-only VMA using
+	 * ptrace(FOLL_FORCE), eventually placing a fresh THP that is marked
+	 * dirty in the PMD.
+	 */
+	lseek(mem_fd, (uintptr_t) mem, SEEK_SET);
+	ret = write(mem_fd, &data, 1);
+	if (ret != 1 || *mem != data) {
+		ksft_test_result_fail("write() failed\n");
+		goto munmap;
+	}
+
+	/* MM populated a THP if we got the last subpage populated as well. */
+	if (!pagemap_is_populated(pagemap_fd, mem + thpsize - pagesize)) {
+		ksft_test_result_skip("Did not get a THP populated\n");
+		goto munmap;
+	}
+
+	do_test_write_sigsegv(mem);
+munmap:
+	munmap(mmap_mem, mmap_size);
+}
+
+static void test_page_migration(void)
+{
+	char *mem;
+
+	ksft_print_msg("[INFO] Page migration\n");
+
+	mem = mmap(NULL, pagesize, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON,
+		   -1, 0);
+	if (mem == MAP_FAILED) {
+		ksft_test_result_fail("mmap() failed\n");
+		return;
+	}
+
+	/* Populate a fresh page and dirty it. */
+	memset(mem, 1, pagesize);
+	if (mprotect(mem, pagesize, PROT_READ)) {
+		ksft_test_result_fail("mprotect() failed\n");
+		goto munmap;
+	}
+
+	/* Trigger page migration. Might not be available or fail. */
+	if (syscall(__NR_mbind, mem, pagesize, MPOL_LOCAL, NULL, 0x7fful,
+		    MPOL_MF_MOVE)) {
+		ksft_test_result_skip("mbind() failed\n");
+		goto munmap;
+	}
+
+	do_test_write_sigsegv(mem);
+munmap:
+	munmap(mem, pagesize);
+}
+
+static void test_page_migration_thp(void)
+{
+	char *mem, *mmap_mem;
+	size_t mmap_size;
+
+	ksft_print_msg("[INFO] Page migration of THP\n");
+
+	mem = mmap_thp_range(PROT_READ|PROT_WRITE, &mmap_mem, &mmap_size);
+	if (mem == MAP_FAILED)
+		return;
+
+	/*
+	 * Write to the first page, which might populate a fresh anon THP
+	 * and dirty it.
+	 */
+	memset(mem, 1, pagesize);
+	if (mprotect(mem, thpsize, PROT_READ)) {
+		ksft_test_result_fail("mprotect() failed\n");
+		goto munmap;
+	}
+
+	/* MM populated a THP if we got the last subpage populated as well. */
+	if (!pagemap_is_populated(pagemap_fd, mem + thpsize - pagesize)) {
+		ksft_test_result_skip("Did not get a THP populated\n");
+		goto munmap;
+	}
+
+	/* Trigger page migration. Might not be available or fail. */
+	if (syscall(__NR_mbind, mem, thpsize, MPOL_LOCAL, NULL, 0x7fful,
+		    MPOL_MF_MOVE)) {
+		ksft_test_result_skip("mbind() failed\n");
+		goto munmap;
+	}
+
+	do_test_write_sigsegv(mem);
+munmap:
+	munmap(mmap_mem, mmap_size);
+}
+
+static void test_pte_mapped_thp(void)
+{
+	char *mem, *mmap_mem;
+	size_t mmap_size;
+
+	ksft_print_msg("[INFO] PTE-mapping a THP\n");
+
+	mem = mmap_thp_range(PROT_READ|PROT_WRITE, &mmap_mem, &mmap_size);
+	if (mem == MAP_FAILED)
+		return;
+
+	/*
+	 * Write to the first page, which might populate a fresh anon THP
+	 * and dirty it.
+	 */
+	memset(mem, 1, pagesize);
+	if (mprotect(mem, thpsize, PROT_READ)) {
+		ksft_test_result_fail("mprotect() failed\n");
+		goto munmap;
+	}
+
+	/* MM populated a THP if we got the last subpage populated as well. */
+	if (!pagemap_is_populated(pagemap_fd, mem + thpsize - pagesize)) {
+		ksft_test_result_skip("Did not get a THP populated\n");
+		goto munmap;
+	}
+
+	/* Trigger PTE-mapping the THP by mprotect'ing the last subpage. */
+	if (mprotect(mem + thpsize - pagesize, pagesize,
+		     PROT_READ|PROT_WRITE)) {
+		ksft_test_result_fail("mprotect() failed\n");
+		goto munmap;
+	}
+
+	do_test_write_sigsegv(mem);
+munmap:
+	munmap(mmap_mem, mmap_size);
+}
+
+#ifdef __NR_userfaultfd
+static void test_uffdio_copy(void)
+{
+	struct uffdio_register uffdio_register;
+	struct uffdio_copy uffdio_copy;
+	struct uffdio_api uffdio_api;
+	char *dst, *src;
+	int uffd;
+
+	ksft_print_msg("[INFO] UFFDIO_COPY\n");
+
+	src = malloc(pagesize);
+	memset(src, 1, pagesize);
+	dst = mmap(NULL, pagesize, PROT_READ, MAP_PRIVATE|MAP_ANON, -1, 0);
+	if (dst == MAP_FAILED) {
+		ksft_test_result_fail("mmap() failed\n");
+		return;
+	}
+
+	uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
+	if (uffd < 0) {
+		ksft_test_result_skip("__NR_userfaultfd failed\n");
+		goto munmap;
+	}
+
+	uffdio_api.api = UFFD_API;
+	uffdio_api.features = 0;
+	if (ioctl(uffd, UFFDIO_API, &uffdio_api) < 0) {
+		ksft_test_result_fail("UFFDIO_API failed\n");
+		goto close_uffd;
+	}
+
+	uffdio_register.range.start = (unsigned long) dst;
+	uffdio_register.range.len = pagesize;
+	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
+	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register)) {
+		ksft_test_result_fail("UFFDIO_REGISTER failed\n");
+		goto close_uffd;
+	}
+
+	/* Place a page in a read-only VMA, which might set the PTE dirty. */
+	uffdio_copy.dst = (unsigned long) dst;
+	uffdio_copy.src = (unsigned long) src;
+	uffdio_copy.len = pagesize;
+	uffdio_copy.mode = 0;
+	if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy)) {
+		ksft_test_result_fail("UFFDIO_COPY failed\n");
+		goto close_uffd;
+	}
+
+	do_test_write_sigsegv(dst);
+close_uffd:
+	close(uffd);
+munmap:
+	munmap(dst, pagesize);
+	free(src);
+#endif /* __NR_userfaultfd */
+}
+
+int main(void)
+{
+	int err, tests = 2;
+
+	pagesize = getpagesize();
+	thpsize = read_pmd_pagesize();
+	if (thpsize) {
+		ksft_print_msg("[INFO] detected THP size: %zu KiB\n",
+			       thpsize / 1024);
+		tests += 3;
+	}
+#ifdef __NR_userfaultfd
+	tests += 1;
+#endif /* __NR_userfaultfd */
+
+	ksft_print_header();
+	ksft_set_plan(tests);
+
+	mem_fd = open("/proc/self/mem", O_RDWR);
+	if (mem_fd < 0)
+		ksft_exit_fail_msg("opening /proc/self/mem failed\n");
+	pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+	if (pagemap_fd < 0)
+		ksft_exit_fail_msg("opening /proc/self/pagemap failed\n");
+
+	/*
+	 * On some ptrace(FOLL_FORCE) write access via /proc/self/mem in
+	 * read-only VMAs, the kernel may set the PTE/PMD dirty.
+	 */
+	test_ptrace_write();
+	if (thpsize)
+		test_ptrace_write_thp();
+	/*
+	 * On page migration, the kernel may set the PTE/PMD dirty when
+	 * remapping the page.
+	 */
+	test_page_migration();
+	if (thpsize)
+		test_page_migration_thp();
+	/* PTE-mapping a THP might propagate the dirty PMD bit to the PTEs. */
+	if (thpsize)
+		test_pte_mapped_thp();
+	/* Placing a fresh page via userfaultfd may set the PTE dirty. */
+#ifdef __NR_userfaultfd
+	test_uffdio_copy();
+#endif /* __NR_userfaultfd */
+
+	err = ksft_get_fail_cnt();
+	if (err)
+		ksft_exit_fail_msg("%d out of %d tests failed\n",
+				   err, ksft_test_num());
+	return ksft_exit_pass();
+}