From: "H. Peter Anvin" <hpa@zytor.com>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>,
tglx@linutronix.de, mingo@redhat.com
Cc: linux-kernel@vger.kernel.org, stefani@seibold.net,
luto@amacapital.net, konrad.wilk@oracle.com,
stable@vger.kernel.org
Subject: Re: [PATCH] time: Cast tv_nsec to u64 for proper shifting in update_vsyscall()
Date: Fri, 09 May 2014 08:43:47 -0700 [thread overview]
Message-ID: <536CF7B3.4040705@zytor.com> (raw)
In-Reply-To: <1399648287-15178-1-git-send-email-boris.ostrovsky@oracle.com>
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?
-hpa
next prev parent reply other threads:[~2014-05-09 15:44 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-09 15:11 [PATCH] time: Cast tv_nsec to u64 for proper shifting in update_vsyscall() Boris Ostrovsky
2014-05-09 15:43 ` H. Peter Anvin [this message]
2014-05-09 15:59 ` Boris Ostrovsky
2014-05-09 16:03 ` H. Peter Anvin
2014-05-09 16:23 ` Boris Ostrovsky
2014-05-09 16:31 ` [tip:x86/urgent] x86, vdso, " tip-bot for Boris Ostrovsky
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