Re: [PATCH v7 02/14] selftests/memfd: Add tests for F_SEAL_AUTO_ALLOCATE

David Hildenbrand
2022-08-05T13:11:56Z

On 06.07.22 10:20, Chao Peng wrote:
> Add tests to verify sealing memfds with the F_SEAL_AUTO_ALLOCATE works
> as expected.
>
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> ---
> tools/testing/selftests/memfd/memfd_test.c | 166 +++++++++++++++++++++
> 1 file changed, 166 insertions(+)
>
> diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
> index 94df2692e6e4..b849ece295fd 100644
> --- a/tools/testing/selftests/memfd/memfd_test.c
> +++ b/tools/testing/selftests/memfd/memfd_test.c
> @@ -9,6 +9,7 @@
> #include <fcntl.h>
> #include <linux/memfd.h>
> #include <sched.h>
> +#include <setjmp.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <signal.h>
> @@ -232,6 +233,31 @@ static void mfd_fail_open(int fd, int flags, mode_t mode)
> }
> }
>
> +static void mfd_assert_fallocate(int fd)
> +{
> + int r;
> +
> + r = fallocate(fd, 0, 0, mfd_def_size);
> + if (r < 0) {
> + printf("fallocate(ALLOC) failed: %m\n");
> + abort();
> + }
> +}
> +
> +static void mfd_assert_punch_hole(int fd)
> +{
> + int r;
> +
> + r = fallocate(fd,
> + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> + 0,
> + mfd_def_size);
> + if (r < 0) {
> + printf("fallocate(PUNCH_HOLE) failed: %m\n");
> + abort();
> + }
> +}
> +
> static void mfd_assert_read(int fd)
> {
> char buf[16];
> @@ -594,6 +620,94 @@ static void mfd_fail_grow_write(int fd)
> }
> }
>
> +static void mfd_assert_hole_write(int fd)
> +{
> + ssize_t l;
> + void *p;
> + char *p1;
> +
> + /*
> + * huegtlbfs does not support write, but we want to
> + * verify everything else here.
> + */
> + if (!hugetlbfs_test) {
> + /* verify direct write() succeeds */
> + l = write(fd, "\0\0\0\0", 4);
> + if (l != 4) {
> + printf("write() failed: %m\n");
> + abort();
> + }
> + }
> +
> + /* verify mmaped write succeeds */
> + p = mmap(NULL,
> + mfd_def_size,
> + PROT_READ | PROT_WRITE,
> + MAP_SHARED,
> + fd,
> + 0);
> + if (p == MAP_FAILED) {
> + printf("mmap() failed: %m\n");
> + abort();
> + }
> + p1 = (char *)p + mfd_def_size - 1;
> + *p1 = 'H';
> + if (*p1 != 'H') {
> + printf("mmaped write failed: %m\n");
> + abort();
> +
> + }
> + munmap(p, mfd_def_size);
> +}
> +
> +sigjmp_buf jbuf, *sigbuf;
> +static void sig_handler(int sig, siginfo_t *siginfo, void *ptr)
> +{
> + if (sig == SIGBUS) {
> + if (sigbuf)
> + siglongjmp(*sigbuf, 1);
> + abort();
> + }
> +}
> +
> +static void mfd_fail_hole_write(int fd)
> +{
> + ssize_t l;
> + void *p;
> + char *p1;
> +
> + /* verify direct write() fails */
> + l = write(fd, "data", 4);
> + if (l > 0) {
> + printf("expected failure on write(), but got %d: %m\n", (int)l);
> + abort();
> + }
> +
> + /* verify mmaped write fails */
> + p = mmap(NULL,
> + mfd_def_size,
> + PROT_READ | PROT_WRITE,
> + MAP_SHARED,
> + fd,
> + 0);
> + if (p == MAP_FAILED) {
> + printf("mmap() failed: %m\n");
> + abort();
> + }
> +
> + sigbuf = &jbuf;
> + if (sigsetjmp(*sigbuf, 1))
> + goto out;
> +
> + /* Below write should trigger SIGBUS signal */
> + p1 = (char *)p + mfd_def_size - 1;
> + *p1 = 'H';

Maybe you want to verify separately, that bothj

> + printf("failed to receive SIGBUS for mmaped write: %m\n");
> + abort();
> +out:
> + munmap(p, mfd_def_size);
> +}
> +
> static int idle_thread_fn(void *arg)
> {
> sigset_t set;
> @@ -880,6 +994,57 @@ static void test_seal_resize(void)
> close(fd);
> }
>
> +/*
> + * Test F_SEAL_AUTO_ALLOCATE
> + * Test whether F_SEAL_AUTO_ALLOCATE actually prevents allocation.
> + */
> +static void test_seal_auto_allocate(void)
> +{
> + struct sigaction act;
> + int fd;
> +
> + printf("%s SEAL-AUTO-ALLOCATE\n", memfd_str);
> +
> + memset(&act, 0, sizeof(act));
> + act.sa_sigaction = sig_handler;
> + act.sa_flags = SA_SIGINFO;
> + if (sigaction(SIGBUS, &act, 0)) {
> + printf("sigaction() failed: %m\n");
> + abort();
> + }
> +
> + fd = mfd_assert_new("kern_memfd_seal_auto_allocate",
> + mfd_def_size,
> + MFD_CLOEXEC | MFD_ALLOW_SEALING);
> +
> + /* read/write should pass if F_SEAL_AUTO_ALLOCATE not set */
> + mfd_assert_read(fd);
> + mfd_assert_hole_write(fd);
> +
> + mfd_assert_has_seals(fd, 0);
> + mfd_assert_add_seals(fd, F_SEAL_AUTO_ALLOCATE);
> + mfd_assert_has_seals(fd, F_SEAL_AUTO_ALLOCATE);
> +
> + /* read/write should pass for pre-allocated area */
> + mfd_assert_read(fd);
> + mfd_assert_hole_write(fd);
> +
> + mfd_assert_punch_hole(fd);
> +
> + /* read should pass, write should fail in hole */
> + mfd_assert_read(fd);
> + mfd_fail_hole_write(fd);
> +
> + mfd_assert_fallocate(fd);
> +
> + /* read/write should pass after fallocate */
> + mfd_assert_read(fd);
> + mfd_assert_hole_write(fd);
> +
> + close(fd);
> +}

What might make sense is to verify for the following operations:
* read()
* write()
* read via mmap
* write via mmap

After sealing on a hole, that there is *still* a hole and that only the
read() might succeed, with a comment stating that shmem optimized for
read on holes by reading from the shared zeropage.

I'd suggest decoupling hole_write from hole_mmap_write and similarly
have hole_read and hole_mmap_read.

You should be able to use fstat() to obtain the number of allocated
blocks to check that fairly easily.

--
Thanks,

David / dhildenb