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

[Dylan Hatch <dylanbhatch@google.com>]

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