[tip:x86/urgent] x86, vdso, time: Cast tv_nsec to u64 for proper shifting in update_vsyscall()
From: tip-bot for Boris Ostrovsky
Date: Fri May 09 2014 - 12:32:01 EST
Commit-ID: 28b92e09e25bdc0ae864b22eacf195a74f861389
Gitweb: http://git.kernel.org/tip/28b92e09e25bdc0ae864b22eacf195a74f861389
Author: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
AuthorDate: Fri, 9 May 2014 11:11:27 -0400
Committer: H. Peter Anvin <hpa@xxxxxxxxx>
CommitDate: Fri, 9 May 2014 08:45:52 -0700
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 <boris.ostrovsky@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1399648287-15178-1-git-send-email-boris.ostrovsky@xxxxxxxxxx
Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v3.14
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
---
arch/x86/kernel/vsyscall_gtod.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/vsyscall_gtod.c b/arch/x86/kernel/vsyscall_gtod.c
index f9c6e56..9531fbb 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)) {
--
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