[tip:timers/urgent] lib/vdso/32: Provide legacy syscall fallbacks

[tip-bot for Thomas Gleixner <tipbot@zytor.com>]

Commit-ID:  c60a32ea4f459f99b98d383cad3b1ac7cfb3f4be
Gitweb:     https://git.kernel.org/tip/c60a32ea4f459f99b98d383cad3b1ac7cfb3f4be
Author:     Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Tue, 30 Jul 2019 11:38:50 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 31 Jul 2019 00:09:09 +0200

lib/vdso/32: Provide legacy syscall fallbacks

To address the regression which causes seccomp to deny applications the
access to clock_gettime64() and clock_getres64() syscalls because they
are not enabled in the existing filters.

That trips over the fact that 32bit VDSOs use the new clock_gettime64() and
clock_getres64() syscalls in the fallback path.

Add a conditional to invoke the 32bit legacy fallback syscalls instead of
the new 64bit variants. The conditional can go away once all architectures
are converted.

Fixes: 00b26474c2f1 ("lib/vdso: Provide generic VDSO implementation")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1907301134470.1738@nanos.tec.linutronix.de

---
 lib/vdso/gettimeofday.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c
index a9e7fd029593..e630e7ff57f1 100644
--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -125,14 +125,18 @@ __cvdso_clock_gettime32(clockid_t clock, struct old_timespec32 *res)
 
 	ret = __cvdso_clock_gettime_common(clock, &ts);
 
+#ifdef VDSO_HAS_32BIT_FALLBACK
+	if (unlikely(ret))
+		return clock_gettime32_fallback(clock, res);
+#else
 	if (unlikely(ret))
 		ret = clock_gettime_fallback(clock, &ts);
+#endif
 
 	if (likely(!ret)) {
 		res->tv_sec = ts.tv_sec;
 		res->tv_nsec = ts.tv_nsec;
 	}
-
 	return ret;
 }
 
@@ -232,8 +236,14 @@ __cvdso_clock_getres_time32(clockid_t clock, struct old_timespec32 *res)
 	int ret;
 
 	ret = __cvdso_clock_getres_common(clock, &ts);
+
+#ifdef VDSO_HAS_32BIT_FALLBACK
+	if (unlikely(ret))
+		return clock_getres32_fallback(clock, res);
+#else
 	if (unlikely(ret))
 		ret = clock_getres_fallback(clock, &ts);
+#endif
 
 	if (likely(!ret)) {
 		res->tv_sec = ts.tv_sec;