Messages in this thread | | | Date | Fri, 09 May 2014 12:23:20 -0400 | From | Boris Ostrovsky <> | Subject | Re: [PATCH] time: Cast tv_nsec to u64 for proper shifting in update_vsyscall() |
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On 05/09/2014 12:03 PM, H. Peter Anvin wrote: > On 05/09/2014 08:59 AM, Boris Ostrovsky wrote: >> On 05/09/2014 11:43 AM, H. Peter Anvin wrote: >>> On 05/09/2014 08:11 AM, Boris Ostrovsky wrote: >>>> 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 explicit cast. >>>> >>>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> >>>> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> >>>> Cc: stable@vger.kernel.org >>> This is needed in stable only for v3.14, right? >> I suspect anything that has commit 650ea024 needs to be fixed. I see >> this code, for example, in 3.12 (it used to be in vsyscall_64.c). >> > But you're talking about 32-bit platforms. Vsyscalls aren't used on > x86-32 until 3.14. Am I missing something?
Oh, yes, of course. I was just looking at code without thinking. 3.14 only then.
-boris
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