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

Dylan Hatch
2022-06-16T21:10:39Z

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.

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 */
--
2.36.1.476.g0c4daa206d-goog