* [PATCH] time: Cast tv_nsec to u64 for proper shifting in update_vsyscall()
@ 2014-05-09 15:11 Boris Ostrovsky
2014-05-09 15:43 ` H. Peter Anvin
0 siblings, 1 reply; 5+ messages in thread
From: Boris Ostrovsky @ 2014-05-09 15:11 UTC (permalink / raw)
To: tglx, mingo, hpa
Cc: linux-kernel, stefani, luto, konrad.wilk, boris.ostrovsky, stable
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
---
arch/x86/kernel/vsyscall_gtod.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
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)) {
--
1.7.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [PATCH] time: Cast tv_nsec to u64 for proper shifting in update_vsyscall()
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
0 siblings, 1 reply; 5+ messages in thread
From: H. Peter Anvin @ 2014-05-09 15:43 UTC (permalink / raw)
To: Boris Ostrovsky, tglx, mingo
Cc: linux-kernel, stefani, luto, konrad.wilk, stable
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
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] time: Cast tv_nsec to u64 for proper shifting in update_vsyscall()
2014-05-09 15:43 ` H. Peter Anvin
@ 2014-05-09 15:59 ` Boris Ostrovsky
2014-05-09 16:03 ` H. Peter Anvin
0 siblings, 1 reply; 5+ messages in thread
From: Boris Ostrovsky @ 2014-05-09 15:59 UTC (permalink / raw)
To: H. Peter Anvin
Cc: tglx, mingo, linux-kernel, stefani, luto, konrad.wilk, stable
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
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] time: Cast tv_nsec to u64 for proper shifting in update_vsyscall()
2014-05-09 15:59 ` Boris Ostrovsky
@ 2014-05-09 16:03 ` H. Peter Anvin
2014-05-09 16:23 ` Boris Ostrovsky
0 siblings, 1 reply; 5+ messages in thread
From: H. Peter Anvin @ 2014-05-09 16:03 UTC (permalink / raw)
To: Boris Ostrovsky
Cc: tglx, mingo, linux-kernel, stefani, luto, konrad.wilk, stable
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?
-hpa
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] time: Cast tv_nsec to u64 for proper shifting in update_vsyscall()
2014-05-09 16:03 ` H. Peter Anvin
@ 2014-05-09 16:23 ` Boris Ostrovsky
0 siblings, 0 replies; 5+ messages in thread
From: Boris Ostrovsky @ 2014-05-09 16:23 UTC (permalink / raw)
To: H. Peter Anvin
Cc: tglx, mingo, linux-kernel, stefani, luto, konrad.wilk, stable
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
^ permalink raw reply [flat|nested] 5+ messages in thread
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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
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2014-05-09 16:03 ` H. Peter Anvin
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