Re: [PATCH] selftests/proc: Fix proc-pid-vm for vsyscall=xonly.

Shuah Khan
2022-06-16T23:01:55Z

On 6/16/22 3:10 PM, Dylan Hatch wrote:
> This test would erroneously fail the /proc/$PID/maps case if
> vsyscall=xonly since the existing probe of the vsyscall page only
> succeeds if the process has read permissions. Fix this by checking for
> either no vsyscall mapping OR an execute-only vsyscall mapping in the
> case were probing the vsyscall page segfaults.
>

Does this fix include skipping the test with a clear message that
says why test is skipped?

> Signed-off-by: Dylan Hatch <dylanbhatch@google.com>
> ---
> tools/testing/selftests/proc/proc-pid-vm.c | 20 +++++++++++++++-----
> 1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/proc/proc-pid-vm.c b/tools/testing/selftests/proc/proc-pid-vm.c
> index 28604c9f805c..5ca85520131f 100644
> --- a/tools/testing/selftests/proc/proc-pid-vm.c
> +++ b/tools/testing/selftests/proc/proc-pid-vm.c
> @@ -213,9 +213,12 @@ static int make_exe(const uint8_t *payload, size_t len)
>
> static bool g_vsyscall = false;
>
> -static const char str_vsyscall[] =
> +static const char str_vsyscall_rx[] =
> "ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]\n";
>
> +static const char str_vsyscall_x[] =
> +"ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0 [vsyscall]\n";
> +
> #ifdef __x86_64__
> static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
> {
> @@ -261,6 +264,7 @@ int main(void)
> int exec_fd;
>
> vsyscall();
> + const char *str_vsyscall = g_vsyscall ? str_vsyscall_rx : str_vsyscall_x;
>
> atexit(ate);
>
> @@ -314,7 +318,8 @@ int main(void)
>
> /* Test /proc/$PID/maps */
> {
> - const size_t len = strlen(buf0) + (g_vsyscall ? strlen(str_vsyscall) : 0);
> + const size_t len_buf0 = strlen(buf0);
> + const size_t len_vsys = strlen(str_vsyscall);
> char buf[256];
> ssize_t rv;
> int fd;
> @@ -325,11 +330,16 @@ int main(void)
> return 1;
> }
> rv = read(fd, buf, sizeof(buf));
> - assert(rv == len);
> - assert(memcmp(buf, buf0, strlen(buf0)) == 0);
> if (g_vsyscall) {
> - assert(memcmp(buf + strlen(buf0), str_vsyscall, strlen(str_vsyscall)) == 0);
> + assert(rv == len_buf0 + len_vsys);
> + } else {
> + /* If vsyscall isn't readable, it's either x-only or not mapped at all */
> + assert(rv == len_buf0 + len_vsys || rv == len_buf0);
> }
> + assert(memcmp(buf, buf0, len_buf0) == 0);
> + /* Check for vsyscall mapping if buf is long enough */
> + if (rv == len_buf0 + len_vsys)
> + assert(memcmp(buf + len_buf0, str_vsyscall, len_vsys) == 0);
> }
>
> /* Test /proc/$PID/smaps */
>

The change looks good to me. Doesn't look like it skips the test though?

thanks,
-- Shuah