The patch titled
Subject: selftests/vm: anon_cow: test COW handling of anonymous memory
has been added to the -mm mm-unstable branch. Its filename is
selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory.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: David Hildenbrand <david@xxxxxxxxxx>
Subject: selftests/vm: anon_cow: test COW handling of anonymous memory
Date: Tue, 27 Sep 2022 13:01:14 +0200
Patch series "selftests/vm: test COW handling of anonymous memory".
This is my current set of tests for testing COW handling of anonymous
memory, especially when interacting with GUP. I developed these tests
while working on PageAnonExclusive and managed to clean them up just now.
On current upstream Linux, all tests pass except the hugetlb tests that
rely on vmsplice -- these tests should pass as soon as vmsplice properly
uses FOLL_PIN instead of FOLL_GET.
I'm working on additional tests for COW handling in private mappings,
focusing on long-term R/O pinning e.g., of the shared zeropage, pagecache
pages and KSM pages. These tests, however, will go into a different file.
So this is everything I have regarding tests for anonymous memory.
This patch (of 7):
Let's start adding tests for our COW handling of anonymous memory. We'll
focus on basic tests that we can achieve without additional libraries or
gup_test extensions.
We'll add THP and hugetlb tests separately.
Link: https://lkml.kernel.org/r/20220927110120.106906-1-david@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20220927110120.106906-2-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Christoph von Recklinghausen <crecklin@xxxxxxxxxx>
Cc: Don Dutile <ddutile@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxx>
Cc: Nadav Amit <namit@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
tools/testing/selftests/vm/.gitignore | 1
tools/testing/selftests/vm/Makefile | 4
tools/testing/selftests/vm/anon_cow.c | 401 ++++++++++++++++++++
tools/testing/selftests/vm/run_vmtests.sh | 3
tools/testing/selftests/vm/vm_util.c | 7
tools/testing/selftests/vm/vm_util.h | 1
6 files changed, 416 insertions(+), 1 deletion(-)
--- /dev/null
+++ a/tools/testing/selftests/vm/anon_cow.c
@@ -0,0 +1,401 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * COW (Copy On Write) tests for anonymous memory.
+ *
+ * Copyright 2022, Red Hat, Inc.
+ *
+ * Author(s): David Hildenbrand <david@xxxxxxxxxx>
+ */
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <dirent.h>
+#include <assert.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+
+#include "../kselftest.h"
+#include "vm_util.h"
+
+static size_t pagesize;
+static int pagemap_fd;
+
+struct comm_pipes {
+ int child_ready[2];
+ int parent_ready[2];
+};
+
+static int setup_comm_pipes(struct comm_pipes *comm_pipes)
+{
+ if (pipe(comm_pipes->child_ready) < 0)
+ return -errno;
+ if (pipe(comm_pipes->parent_ready) < 0) {
+ close(comm_pipes->child_ready[0]);
+ close(comm_pipes->child_ready[1]);
+ return -errno;
+ }
+
+ return 0;
+}
+
+static void close_comm_pipes(struct comm_pipes *comm_pipes)
+{
+ close(comm_pipes->child_ready[0]);
+ close(comm_pipes->child_ready[1]);
+ close(comm_pipes->parent_ready[0]);
+ close(comm_pipes->parent_ready[1]);
+}
+
+static int child_memcmp_fn(char *mem, size_t size,
+ struct comm_pipes *comm_pipes)
+{
+ char *old = malloc(size);
+ char buf;
+
+ /* Backup the original content. */
+ memcpy(old, mem, size);
+
+ /* Wait until the parent modified the page. */
+ write(comm_pipes->child_ready[1], "0", 1);
+ while (read(comm_pipes->parent_ready[0], &buf, 1) != 1)
+ ;
+
+ /* See if we still read the old values. */
+ return memcmp(old, mem, size);
+}
+
+static int child_vmsplice_memcmp_fn(char *mem, size_t size,
+ struct comm_pipes *comm_pipes)
+{
+ struct iovec iov = {
+ .iov_base = mem,
+ .iov_len = size,
+ };
+ size_t cur, total, transferred;
+ char *old, *new;
+ int fds[2];
+ char buf;
+
+ old = malloc(size);
+ new = malloc(size);
+
+ /* Backup the original content. */
+ memcpy(old, mem, size);
+
+ if (pipe(fds) < 0)
+ return -errno;
+
+ /* Trigger a read-only pin. */
+ transferred = vmsplice(fds[1], &iov, 1, 0);
+ if (transferred < 0)
+ return -errno;
+ if (transferred == 0)
+ return -EINVAL;
+
+ /* Unmap it from our page tables. */
+ if (munmap(mem, size) < 0)
+ return -errno;
+
+ /* Wait until the parent modified it. */
+ write(comm_pipes->child_ready[1], "0", 1);
+ while (read(comm_pipes->parent_ready[0], &buf, 1) != 1)
+ ;
+
+ /* See if we still read the old values via the pipe. */
+ for (total = 0; total < transferred; total += cur) {
+ cur = read(fds[0], new + total, transferred - total);
+ if (cur < 0)
+ return -errno;
+ }
+
+ return memcmp(old, new, transferred);
+}
+
+typedef int (*child_fn)(char *mem, size_t size, struct comm_pipes *comm_pipes);
+
+static void do_test_cow_in_parent(char *mem, size_t size, child_fn fn)
+{
+ struct comm_pipes comm_pipes;
+ char buf;
+ int ret;
+
+ ret = setup_comm_pipes(&comm_pipes);
+ if (ret) {
+ ksft_test_result_fail("pipe() failed\n");
+ return;
+ }
+
+ ret = fork();
+ if (ret < 0) {
+ ksft_test_result_fail("fork() failed\n");
+ goto close_comm_pipes;
+ } else if (!ret) {
+ exit(fn(mem, size, &comm_pipes));
+ }
+
+ while (read(comm_pipes.child_ready[0], &buf, 1) != 1)
+ ;
+ /* Modify the page. */
+ memset(mem, 0xff, size);
+ write(comm_pipes.parent_ready[1], "0", 1);
+
+ wait(&ret);
+ if (WIFEXITED(ret))
+ ret = WEXITSTATUS(ret);
+ else
+ ret = -EINVAL;
+
+ ksft_test_result(!ret, "No leak from parent into child\n");
+close_comm_pipes:
+ close_comm_pipes(&comm_pipes);
+}
+
+static void test_cow_in_parent(char *mem, size_t size)
+{
+ do_test_cow_in_parent(mem, size, child_memcmp_fn);
+}
+
+static void test_vmsplice_in_child(char *mem, size_t size)
+{
+ do_test_cow_in_parent(mem, size, child_vmsplice_memcmp_fn);
+}
+
+static void do_test_vmsplice_in_parent(char *mem, size_t size,
+ bool before_fork)
+{
+ struct iovec iov = {
+ .iov_base = mem,
+ .iov_len = size,
+ };
+ size_t cur, total, transferred;
+ struct comm_pipes comm_pipes;
+ char *old, *new;
+ int ret, fds[2];
+ char buf;
+
+ old = malloc(size);
+ new = malloc(size);
+
+ memcpy(old, mem, size);
+
+ ret = setup_comm_pipes(&comm_pipes);
+ if (ret) {
+ ksft_test_result_fail("pipe() failed\n");
+ goto free;
+ }
+
+ if (pipe(fds) < 0) {
+ ksft_test_result_fail("pipe() failed\n");
+ goto close_comm_pipes;
+ }
+
+ if (before_fork) {
+ transferred = vmsplice(fds[1], &iov, 1, 0);
+ if (transferred <= 0) {
+ ksft_test_result_fail("vmsplice() failed\n");
+ goto close_pipe;
+ }
+ }
+
+ ret = fork();
+ if (ret < 0) {
+ ksft_test_result_fail("fork() failed\n");
+ goto close_pipe;
+ } else if (!ret) {
+ write(comm_pipes.child_ready[1], "0", 1);
+ while (read(comm_pipes.parent_ready[0], &buf, 1) != 1)
+ ;
+ /* Modify page content in the child. */
+ memset(mem, 0xff, size);
+ exit(0);
+ }
+
+ if (!before_fork) {
+ transferred = vmsplice(fds[1], &iov, 1, 0);
+ if (transferred <= 0) {
+ ksft_test_result_fail("vmsplice() failed\n");
+ wait(&ret);
+ goto close_pipe;
+ }
+ }
+
+ while (read(comm_pipes.child_ready[0], &buf, 1) != 1)
+ ;
+ if (munmap(mem, size) < 0) {
+ ksft_test_result_fail("munmap() failed\n");
+ goto close_pipe;
+ }
+ write(comm_pipes.parent_ready[1], "0", 1);
+
+ /* Wait until the child is done writing. */
+ wait(&ret);
+ if (!WIFEXITED(ret)) {
+ ksft_test_result_fail("wait() failed\n");
+ goto close_pipe;
+ }
+
+ /* See if we still read the old values. */
+ for (total = 0; total < transferred; total += cur) {
+ cur = read(fds[0], new + total, transferred - total);
+ if (cur < 0) {
+ ksft_test_result_fail("read() failed\n");
+ goto close_pipe;
+ }
+ }
+
+ ksft_test_result(!memcmp(old, new, transferred),
+ "No leak from child into parent\n");
+close_pipe:
+ close(fds[0]);
+ close(fds[1]);
+close_comm_pipes:
+ close_comm_pipes(&comm_pipes);
+free:
+ free(old);
+ free(new);
+}
+
+static void test_vmsplice_before_fork(char *mem, size_t size)
+{
+ do_test_vmsplice_in_parent(mem, size, true);
+}
+
+static void test_vmsplice_after_fork(char *mem, size_t size)
+{
+ do_test_vmsplice_in_parent(mem, size, false);
+}
+
+typedef void (*test_fn)(char *mem, size_t size);
+
+static void do_run_with_base_page(test_fn fn, bool swapout)
+{
+ char *mem;
+ int ret;
+
+ mem = mmap(NULL, pagesize, PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (mem == MAP_FAILED) {
+ ksft_test_result_fail("mmap() failed\n");
+ return;
+ }
+
+ ret = madvise(mem, pagesize, MADV_NOHUGEPAGE);
+ /* Ignore if not around on a kernel. */
+ if (ret && errno != EINVAL) {
+ ksft_test_result_fail("MADV_NOHUGEPAGE failed\n");
+ goto munmap;
+ }
+
+ /* Populate a base page. */
+ memset(mem, 0, pagesize);
+
+ if (swapout) {
+ madvise(mem, pagesize, MADV_PAGEOUT);
+ if (!pagemap_is_swapped(pagemap_fd, mem)) {
+ ksft_test_result_skip("MADV_PAGEOUT did not work, is swap enabled?\n");
+ goto munmap;
+ }
+ }
+
+ fn(mem, pagesize);
+munmap:
+ munmap(mem, pagesize);
+}
+
+static void run_with_base_page(test_fn fn, const char *desc)
+{
+ ksft_print_msg("[RUN] %s ... with base page\n", desc);
+ do_run_with_base_page(fn, false);
+}
+
+static void run_with_base_page_swap(test_fn fn, const char *desc)
+{
+ ksft_print_msg("[RUN] %s ... with swapped out base page\n", desc);
+ do_run_with_base_page(fn, true);
+}
+
+struct test_case {
+ const char *desc;
+ test_fn fn;
+};
+
+static const struct test_case test_cases[] = {
+ /*
+ * Basic COW tests for fork() without any GUP. If we miss to break COW,
+ * either the child can observe modifications by the parent or the
+ * other way around.
+ */
+ {
+ "Basic COW after fork()",
+ test_cow_in_parent,
+ },
+ /*
+ * vmsplice() [R/O GUP] + unmap in the child; modify in the parent. If
+ * we miss to break COW, the child observes modifications by the parent.
+ * This is CVE-2020-29374 reported by Jann Horn.
+ */
+ {
+ "vmsplice() + unmap in child",
+ test_vmsplice_in_child
+ },
+ /*
+ * vmsplice() [R/O GUP] in parent before fork(), unmap in parent after
+ * fork(); modify in the child. If we miss to break COW, the parent
+ * observes modifications by the child.
+ */
+ {
+ "vmsplice() before fork(), unmap in parent after fork()",
+ test_vmsplice_before_fork,
+ },
+ /*
+ * vmsplice() [R/O GUP] + unmap in parent after fork(); modify in the
+ * child. If we miss to break COW, the parent observes modifications by
+ * the child.
+ */
+ {
+ "vmsplice() + unmap in parent after fork()",
+ test_vmsplice_after_fork,
+ },
+};
+
+static void run_test_case(struct test_case const *test_case)
+{
+ run_with_base_page(test_case->fn, test_case->desc);
+ run_with_base_page_swap(test_case->fn, test_case->desc);
+}
+
+static void run_test_cases(void)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(test_cases); i++)
+ run_test_case(&test_cases[i]);
+}
+
+int main(int argc, char **argv)
+{
+ int nr_test_cases = ARRAY_SIZE(test_cases);
+ int err;
+
+ pagesize = getpagesize();
+
+ ksft_print_header();
+ ksft_set_plan(nr_test_cases * 2);
+
+ pagemap_fd = open("/proc/self/pagemap", O_RDONLY);
+ if (pagemap_fd < 0)
+ ksft_exit_fail_msg("opening pagemap failed\n");
+
+ run_test_cases();
+
+ 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();
+}
--- a/tools/testing/selftests/vm/.gitignore~selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory
+++ a/tools/testing/selftests/vm/.gitignore
@@ -1,4 +1,5 @@
# SPDX-License-Identifier: GPL-2.0-only
+anon_cow
hugepage-mmap
hugepage-mremap
hugepage-shm
--- a/tools/testing/selftests/vm/Makefile~selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory
+++ a/tools/testing/selftests/vm/Makefile
@@ -25,7 +25,8 @@ MAKEFLAGS += --no-builtin-rules
CFLAGS = -Wall -I $(top_srcdir) -I $(top_srcdir)/usr/include $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
LDLIBS = -lrt -lpthread
-TEST_GEN_FILES = compaction_test
+TEST_GEN_FILES = anon_cow
+TEST_GEN_FILES += compaction_test
TEST_GEN_FILES += gup_test
TEST_GEN_FILES += hmm-tests
TEST_GEN_FILES += hugetlb-madvise
@@ -95,6 +96,7 @@ TEST_FILES += va_128TBswitch.sh
include ../lib.mk
+$(OUTPUT)/anon_cow: vm_util.c
$(OUTPUT)/khugepaged: vm_util.c
$(OUTPUT)/madv_populate: vm_util.c
$(OUTPUT)/soft-dirty: vm_util.c
--- a/tools/testing/selftests/vm/run_vmtests.sh~selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory
+++ a/tools/testing/selftests/vm/run_vmtests.sh
@@ -185,4 +185,7 @@ fi
run_test ./soft-dirty
+# COW tests for anonymous memory
+run_test ./anon_cow
+
exit $exitcode
--- a/tools/testing/selftests/vm/vm_util.c~selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory
+++ a/tools/testing/selftests/vm/vm_util.c
@@ -28,6 +28,13 @@ bool pagemap_is_softdirty(int fd, char *
return entry & 0x0080000000000000ull;
}
+bool pagemap_is_swapped(int fd, char *start)
+{
+ uint64_t entry = pagemap_get_entry(fd, start);
+
+ return entry & 0x4000000000000000ull;
+}
+
void clear_softdirty(void)
{
int ret;
--- a/tools/testing/selftests/vm/vm_util.h~selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory
+++ a/tools/testing/selftests/vm/vm_util.h
@@ -4,6 +4,7 @@
uint64_t pagemap_get_entry(int fd, char *start);
bool pagemap_is_softdirty(int fd, char *start);
+bool pagemap_is_swapped(int fd, char *start);
void clear_softdirty(void);
bool check_for_pattern(FILE *fp, const char *pattern, char *buf, size_t len);
uint64_t read_pmd_pagesize(void);
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
selftests-vm-add-test-to-measure-madv_unmergeable-performance.patch
mm-ksm-simplify-break_ksm-to-not-rely-on-vm_fault_write.patch
mm-remove-vm_fault_write.patch
mm-ksm-fix-ksm-cow-breaking-with-userfaultfd-wp-via-fault_flag_unshare.patch
mm-pagewalk-add-walk_page_range_vma.patch
mm-ksm-convert-break_ksm-to-use-walk_page_range_vma.patch
mm-gup-remove-foll_migration.patch
selftests-vm-anon_cow-test-cow-handling-of-anonymous-memory.patch
selftests-vm-factor-out-pagemap_is_populated-into-vm_util.patch
selftests-vm-anon_cow-thp-tests.patch
selftests-vm-anon_cow-hugetlb-tests.patch
selftests-vm-anon_cow-add-liburing-test-cases.patch
mm-gup_test-start-stop-read-functionality-for-pin-longterm-test.patch
selftests-vm-anon_cow-add-r-o-longterm-tests-via-gup_test.patch
