From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: tglx@linutronix.de, mingo@redhat.com,
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 11:59:53 -0400 [thread overview]
Message-ID: <536CFB79.7030602@oracle.com> (raw)
In-Reply-To: <536CF7B3.4040705@zytor.com>
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).
-boris
next prev parent reply other threads:[~2014-05-09 15:59 UTC|newest]
Thread overview: 5+ 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
2014-05-09 15:59 ` Boris Ostrovsky [this message]
2014-05-09 16:03 ` H. Peter Anvin
2014-05-09 16:23 ` Boris Ostrovsky
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