Re: [PATCH v1 1/7] selftests/vm: anon_cow: test COW handling of anonymous memory

From: Rafael Mendonca
Date: Mon Oct 24 2022 - 14:18:07 EST

Next message: matthew . gerlach: "Re: [PATCH v4 2/4] fpga: dfl: Add DFHv1 Register Definitions"
Previous message: Dennis Zhou: "Re: [PATCH 4/8] mm/percpu: add comment to state the empty populated pages accounting"
Next in thread: David Hildenbrand: "Re: [PATCH v1 1/7] selftests/vm: anon_cow: test COW handling of anonymous memory"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

On Tue, Sep 27, 2022 at 01:01:14PM +0200, David Hildenbrand wrote:
> 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.
>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> 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(-)
> create mode 100644 tools/testing/selftests/vm/anon_cow.c
>
> diff --git a/tools/testing/selftests/vm/.gitignore b/tools/testing/selftests/vm/.gitignore
> index 7b9dc2426f18..8a536c731e3c 100644
> --- a/tools/testing/selftests/vm/.gitignore
> +++ b/tools/testing/selftests/vm/.gitignore
> @@ -1,4 +1,5 @@
> # SPDX-License-Identifier: GPL-2.0-only
> +anon_cow
> hugepage-mmap
> hugepage-mremap
> hugepage-shm
> diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
> index 4ae879f70f4c..bc759534ec28 100644
> --- a/tools/testing/selftests/vm/Makefile
> +++ b/tools/testing/selftests/vm/Makefile
> @@ -25,7 +25,8 @@ MAKEFLAGS += --no-builtin-rules
>
> CFLAGS = -Wall -I ../../../../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)/madv_populate: vm_util.c
> $(OUTPUT)/soft-dirty: vm_util.c
> $(OUTPUT)/split_huge_page_test: vm_util.c
> diff --git a/tools/testing/selftests/vm/anon_cow.c b/tools/testing/selftests/vm/anon_cow.c
> new file mode 100644
> index 000000000000..9d2b15c829e6
> --- /dev/null
> +++ b/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)

Hi David,
I was looking at some coccinelle reports for linux-next and
saw the following warning for this comparison:

WARNING: Unsigned expression compared with zero: cur < 0

I think 'cur' needs to be of type 'ssize_t' for this comparison to work.

The same warning is reported for the variable 'transferred' above, and
also for do_test_iouring() and do_test_vmsplice_in_parent() in
"selftests/vm: anon_cow: add liburing test cases".

> + 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();
> +}
> diff --git a/tools/testing/selftests/vm/run_vmtests.sh b/tools/testing/selftests/vm/run_vmtests.sh
> index e780e76c26b8..af59380bc254 100755
> --- a/tools/testing/selftests/vm/run_vmtests.sh
> +++ b/tools/testing/selftests/vm/run_vmtests.sh
> @@ -197,4 +197,7 @@ fi
>
> run_test ./soft-dirty
>
> +# COW tests for anonymous memory
> +run_test ./anon_cow
> +
> exit $exitcode
> diff --git a/tools/testing/selftests/vm/vm_util.c b/tools/testing/selftests/vm/vm_util.c
> index b58ab11a7a30..6456027e1985 100644
> --- a/tools/testing/selftests/vm/vm_util.c
> +++ b/tools/testing/selftests/vm/vm_util.c
> @@ -28,6 +28,13 @@ bool pagemap_is_softdirty(int fd, char *start)
> 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;
> diff --git a/tools/testing/selftests/vm/vm_util.h b/tools/testing/selftests/vm/vm_util.h
> index 2e512bd57ae1..bb8ec8d69623 100644
> --- a/tools/testing/selftests/vm/vm_util.h
> +++ b/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);
> uint64_t read_pmd_pagesize(void);
> uint64_t check_huge(void *addr);
> --
> 2.37.3
>

Next message: matthew . gerlach: "Re: [PATCH v4 2/4] fpga: dfl: Add DFHv1 Register Definitions"
Previous message: Dennis Zhou: "Re: [PATCH 4/8] mm/percpu: add comment to state the empty populated pages accounting"
Next in thread: David Hildenbrand: "Re: [PATCH v1 1/7] selftests/vm: anon_cow: test COW handling of anonymous memory"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]