From: Boris Ostrovsky Date: Fri, 9 May 2014 15:11:27 +0000 (-0400) Subject: x86, vdso, time: Cast tv_nsec to u64 for proper shifting in update_vsyscall() X-Git-Tag: firefly_0821_release~176^2~3927^2 X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=28b92e09e25bdc0ae864b22eacf195a74f861389;p=firefly-linux-kernel-4.4.55.git x86, vdso, time: Cast tv_nsec to u64 for proper shifting in update_vsyscall() With tk->wall_to_monotonic.tv_nsec being a 32-bit value on 32-bit systems, (tk->wall_to_monotonic.tv_nsec << tk->shift) in update_vsyscall() may lose upper bits or, worse, add them since compiler will do this: (u64)(tk->wall_to_monotonic.tv_nsec << tk->shift) instead of ((u64)tk->wall_to_monotonic.tv_nsec << tk->shift) So if, for example, tv_nsec is 0x800000 and shift is 8 we will end up with 0xffffffff80000000 instead of 0x80000000. And then we are stuck in the subsequent 'while' loop. We need an explicit cast. Signed-off-by: Boris Ostrovsky Link: http://lkml.kernel.org/r/1399648287-15178-1-git-send-email-boris.ostrovsky@oracle.com Acked-by: Konrad Rzeszutek Wilk Cc: # v3.14 Signed-off-by: H. Peter Anvin --- diff --git a/arch/x86/kernel/vsyscall_gtod.c b/arch/x86/kernel/vsyscall_gtod.c index f9c6e56e14b5..9531fbb123ba 100644 --- a/arch/x86/kernel/vsyscall_gtod.c +++ b/arch/x86/kernel/vsyscall_gtod.c @@ -43,7 +43,7 @@ void update_vsyscall(struct timekeeper *tk) vdata->monotonic_time_sec = tk->xtime_sec + tk->wall_to_monotonic.tv_sec; vdata->monotonic_time_snsec = tk->xtime_nsec - + (tk->wall_to_monotonic.tv_nsec + + ((u64)tk->wall_to_monotonic.tv_nsec << tk->shift); while (vdata->monotonic_time_snsec >= (((u64)NSEC_PER_SEC) << tk->shift)) {