[PATCH] x86/vdso: Fix vDSO syscall fallback asm constraint regression

[Andy Lutomirski <luto@kernel.org>]

When I added the missing memory outputs, I failed to update the
index of the first argument (ebx) on 32-bit builds, which broke the
fallbacks.  Somehow I must have screwed up my testing or gotten
lucky.

Add another test to cover gettimeofday() as well.

Cc: stable@vger.kernel.org
Fixes: 715bd9d12f84 ("x86/vdso: Fix asm constraints on vDSO syscall fallbacks")
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/entry/vdso/vclock_gettime.c    |  8 +--
 tools/testing/selftests/x86/test_vdso.c | 73 +++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 4 deletions(-)

diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c
index 134e2d2e8add..e48ca3afa091 100644
--- a/arch/x86/entry/vdso/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vclock_gettime.c
@@ -68,11 +68,11 @@ notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
 
 	asm (
 		"mov %%ebx, %%edx \n"
-		"mov %2, %%ebx \n"
+		"mov %[clock], %%ebx \n"
 		"call __kernel_vsyscall \n"
 		"mov %%edx, %%ebx \n"
 		: "=a" (ret), "=m" (*ts)
-		: "0" (__NR_clock_gettime), "g" (clock), "c" (ts)
+		: "0" (__NR_clock_gettime), [clock] "g" (clock), "c" (ts)
 		: "memory", "edx");
 	return ret;
 }
@@ -83,11 +83,11 @@ notrace static long vdso_fallback_gtod(struct timeval *tv, struct timezone *tz)
 
 	asm (
 		"mov %%ebx, %%edx \n"
-		"mov %2, %%ebx \n"
+		"mov %[tv], %%ebx \n"
 		"call __kernel_vsyscall \n"
 		"mov %%edx, %%ebx \n"
 		: "=a" (ret), "=m" (*tv), "=m" (*tz)
-		: "0" (__NR_gettimeofday), "g" (tv), "c" (tz)
+		: "0" (__NR_gettimeofday), [tv] "g" (tv), "c" (tz)
 		: "memory", "edx");
 	return ret;
 }
diff --git a/tools/testing/selftests/x86/test_vdso.c b/tools/testing/selftests/x86/test_vdso.c
index 49f7294fb382..35edd61d1663 100644
--- a/tools/testing/selftests/x86/test_vdso.c
+++ b/tools/testing/selftests/x86/test_vdso.c
@@ -36,6 +36,10 @@ typedef int (*vgettime_t)(clockid_t, struct timespec *);
 
 vgettime_t vdso_clock_gettime;
 
+typedef long (*vgtod_t)(struct timeval *tv, struct timezone *tz);
+
+vgtod_t vdso_gettimeofday;
+
 typedef long (*getcpu_t)(unsigned *, unsigned *, void *);
 
 getcpu_t vgetcpu;
@@ -104,6 +108,11 @@ static void fill_function_pointers()
 	vdso_clock_gettime = (vgettime_t)dlsym(vdso, "__vdso_clock_gettime");
 	if (!vdso_clock_gettime)
 		printf("Warning: failed to find clock_gettime in vDSO\n");
+
+	vdso_gettimeofday = (vgtod_t)dlsym(vdso, "__vdso_gettimeofday");
+	if (!vdso_gettimeofday)
+		printf("Warning: failed to find gettimeofday in vDSO\n");
+
 }
 
 static long sys_getcpu(unsigned * cpu, unsigned * node,
@@ -117,6 +126,11 @@ static inline int sys_clock_gettime(clockid_t id, struct timespec *ts)
 	return syscall(__NR_clock_gettime, id, ts);
 }
 
+static inline int sys_gettimeofday(struct timeval *tv, struct timezone *tz)
+{
+	return syscall(__NR_gettimeofday, tv, tz);
+}
+
 static void test_getcpu(void)
 {
 	printf("[RUN]\tTesting getcpu...\n");
@@ -177,6 +191,14 @@ static bool ts_leq(const struct timespec *a, const struct timespec *b)
 		return a->tv_nsec <= b->tv_nsec;
 }
 
+static bool tv_leq(const struct timeval *a, const struct timeval *b)
+{
+	if (a->tv_sec != b->tv_sec)
+		return a->tv_sec < b->tv_sec;
+	else
+		return a->tv_usec <= b->tv_usec;
+}
+
 static char const * const clocknames[] = {
 	[0] = "CLOCK_REALTIME",
 	[1] = "CLOCK_MONOTONIC",
@@ -248,11 +270,62 @@ static void test_clock_gettime(void)
 	test_one_clock_gettime(INT_MAX, "invalid");
 }
 
+static void test_gettimeofday(void)
+{
+	struct timeval start, vdso, end;
+	struct timezone sys_tz, vdso_tz;
+	int vdso_ret, end_ret;
+
+	if (!vdso_gettimeofday)
+		return;
+
+	printf("[RUN]\tTesting gettimeofday...\n");
+
+	if (sys_gettimeofday(&start, &sys_tz) < 0) {
+		printf("[FAIL]\tsys_gettimeofday failed (%d)\n", errno);
+		nerrs++;
+		return;
+	}
+
+	vdso_ret = vdso_gettimeofday(&vdso, &vdso_tz);
+	end_ret = sys_gettimeofday(&end, NULL);
+
+	if (vdso_ret != 0 || end_ret != 0) {
+		printf("[FAIL]\tvDSO returned %d, syscall errno=%d\n",
+		       vdso_ret, errno);
+		nerrs++;
+		return;
+	}
+
+	printf("\t%llu.%06ld %llu.%06ld %llu.%06ld\n",
+	       (unsigned long long)start.tv_sec, start.tv_usec,
+	       (unsigned long long)vdso.tv_sec, vdso.tv_usec,
+	       (unsigned long long)end.tv_sec, end.tv_usec);
+
+	if (!tv_leq(&start, &vdso) || !tv_leq(&vdso, &end)) {
+		printf("[FAIL]\tTimes are out of sequence\n");
+		nerrs++;
+	}
+
+	if (sys_tz.tz_minuteswest == vdso_tz.tz_minuteswest &&
+	    sys_tz.tz_dsttime == vdso_tz.tz_dsttime) {
+		printf("[OK]\ttimezones match: minuteswest=%d, dsttime=%d\n",
+		       sys_tz.tz_minuteswest, sys_tz.tz_dsttime);
+	} else {
+		printf("[FAIL]\ttimezones do not match\n");
+		nerrs++;
+	}
+
+	/* And make sure that passing NULL for tz doesn't crash. */
+	vdso_gettimeofday(&vdso, NULL);
+}
+
 int main(int argc, char **argv)
 {
 	fill_function_pointers();
 
 	test_clock_gettime();
+	test_gettimeofday();
 
 	/*
 	 * Test getcpu() last so that, if something goes wrong setting affinity,
-- 
2.17.1