linux-kernel - [patch V2 3/5] lib/vdso/32: Provide legacy syscall fallbacks

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Message-ID: <alpine.DEB.2.21.1907301134470.1738@nanos.tec.linutronix.de>
Date:   Tue, 30 Jul 2019 11:38:50 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Kees Cook <keescook@...omium.org>,
        Paul Bolle <pebolle@...cali.nl>, Will Deacon <will@...nel.org>
Subject: [patch V2 3/5] 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@...utronix.de>
---
V2: Move the #ifdef into the fallback function
---
 lib/vdso/gettimeofday.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/lib/vdso/gettimeofday.c
+++ b/lib/vdso/gettimeofday.c
@@ -125,14 +125,18 @@ static __maybe_unused int
 
 	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 @@ static __maybe_unused int
 	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;