linux-kernel - [PATCH] selftests/proc: Add support for vsyscall=xonly

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Date:   Sat,  6 Aug 2022 22:57:49 +0900
From:   Shigeru Yoshida <syoshida@...hat.com>
To:     shuah@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Shigeru Yoshida <syoshida@...hat.com>
Subject: [PATCH] selftests/proc: Add support for vsyscall=xonly

There are 3 vsyscall modes: emulate, xonly, and none.  proc-pid-vm
detects the existence of the vsyscall with memory load on the vsyscall
page.

This works for emulate and none vsyscall modes, but fails for xonly
because read permission is omitted with xonly vsyscall page, and it
results in the following error:

  # ./proc-pid-vm
  proc-pid-vm: proc-pid-vm.c:328: main: Assertion `rv == len' failed.
  Aborted (core dumped)

This patch fixes this issue with introducing the following rule:

  1. vsyscall mode is emulate if it can load memory
  2. vsyscall mode is xonly if it can call gettimeofday() on vsyscall
  3. vsyscall mode is node otherwise

Signed-off-by: Shigeru Yoshida <syoshida@...hat.com>
---
 tools/testing/selftests/proc/proc-pid-vm.c | 77 ++++++++++++++++++----
 1 file changed, 65 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/proc/proc-pid-vm.c b/tools/testing/selftests/proc/proc-pid-vm.c
index 28604c9f805c..dffd263beef3 100644
--- a/tools/testing/selftests/proc/proc-pid-vm.c
+++ b/tools/testing/selftests/proc/proc-pid-vm.c
@@ -211,10 +211,16 @@ static int make_exe(const uint8_t *payload, size_t len)
 }
 #endif
 
-static bool g_vsyscall = false;
-
-static const char str_vsyscall[] =
-"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]\n";
+static enum { EMULATE, XONLY, NONE } g_vsyscall_mode;
+
+static const char * const str_vsyscall[] = {
+	/* emulate */
+	"ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]\n",
+	/* xonly */
+	"ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0                  [vsyscall]\n",
+	/* none */
+	"",
+};
 
 #ifdef __x86_64__
 static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
@@ -225,7 +231,33 @@ static void sigaction_SIGSEGV(int _, siginfo_t *__, void *___)
 /*
  * vsyscall page can't be unmapped, probe it with memory load.
  */
-static void vsyscall(void)
+static bool vsyscall_emulate(void)
+{
+	*(volatile int *)0xffffffffff600000UL;
+	return true;
+}
+
+/*
+ * vsyscall page can't be unmapped, probe it with calling gettimeofday().
+ */
+static bool vsyscall_xonly(void)
+{
+	int ret;
+	struct timeval tv;
+	int (*f)(struct timeval *tv, struct timezone *tz);
+
+	/* Try to call gettimeofday() on vsyscall*/
+	f = (void *)0xffffffffff600000UL;
+	ret = f(&tv, NULL);
+	if (ret < 0) {
+		fprintf(stderr, "gettimeofday() on vsyscall, ret %d\n", ret);
+		return false;
+	}
+
+	return true;
+}
+
+static bool vsyscall_test(bool (*test)(void))
 {
 	pid_t pid;
 	int wstatus;
@@ -246,13 +278,27 @@ static void vsyscall(void)
 		act.sa_sigaction = sigaction_SIGSEGV;
 		(void)sigaction(SIGSEGV, &act, NULL);
 
-		*(volatile int *)0xffffffffff600000UL;
+		if (!test())
+			exit(1);
+
 		exit(0);
 	}
 	waitpid(pid, &wstatus, 0);
 	if (WIFEXITED(wstatus) && WEXITSTATUS(wstatus) == 0) {
-		g_vsyscall = true;
+		return true;
 	}
+
+	return false;
+}
+
+static void vsyscall(void)
+{
+	if (vsyscall_test(vsyscall_emulate))
+		g_vsyscall_mode = EMULATE;
+	else if (vsyscall_test(vsyscall_xonly))
+		g_vsyscall_mode = XONLY;
+	else
+		g_vsyscall_mode = NONE;
 }
 
 int main(void)
@@ -314,11 +360,14 @@ int main(void)
 
 	/* Test /proc/$PID/maps */
 	{
-		const size_t len = strlen(buf0) + (g_vsyscall ? strlen(str_vsyscall) : 0);
+		size_t len = strlen(buf0);
 		char buf[256];
 		ssize_t rv;
 		int fd;
 
+		if (g_vsyscall_mode != NONE)
+			len += strlen(str_vsyscall[g_vsyscall_mode]);
+
 		snprintf(buf, sizeof(buf), "/proc/%u/maps", pid);
 		fd = open(buf, O_RDONLY);
 		if (fd == -1) {
@@ -327,8 +376,10 @@ int main(void)
 		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);
+		if (g_vsyscall_mode != NONE) {
+			assert(memcmp(buf + strlen(buf0),
+				      str_vsyscall[g_vsyscall_mode],
+				      strlen(str_vsyscall[g_vsyscall_mode])) == 0);
 		}
 	}
 
@@ -374,8 +425,10 @@ int main(void)
 			assert(memmem(buf, rv, S[i], strlen(S[i])));
 		}
 
-		if (g_vsyscall) {
-			assert(memmem(buf, rv, str_vsyscall, strlen(str_vsyscall)));
+		if (g_vsyscall_mode != NONE) {
+			assert(memmem(buf, rv,
+				      str_vsyscall[g_vsyscall_mode],
+				      strlen(str_vsyscall[g_vsyscall_mode])));
 		}
 	}
 
-- 
2.37.1