linux-kernel - Re: [PATCH] x86, mpx: Ensure unused arguments of prctl() MPX requests are 0

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Date:	Fri, 9 Jan 2015 19:25:43 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Qiaowei Ren <qiaowei.ren@...el.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, mpx: Ensure unused arguments of prctl() MPX requests
 are 0

On 9 January 2015 at 18:25, Andi Kleen <andi@...stfloor.org> wrote:
> "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> writes:
>
>> From: Michael Kerrisk <mtk.manpages@...il.com>
>>
>> commit fe8c7f5cbf91124987106faa3bdf0c8b955c4cf7 added two new prctl()
>> operations, PR_MPX_ENABLE_MANAGEMENT and PR_MPX_DISABLE_MANAGEMENT.
>> However, no checks were included to ensure that unused arguments
>> are zero, as is done in many existing prctl()s and as should be
>> done for all new prctl()s. This patch adds the required checks.
>
> This will break the existing gcc run time, which doesn't zero these
> arguments.

I'm a little lost here. Weren't these flags new in the
as-yet-unreleased 3.19? How does gcc run-time depends on them already?

Thanks,

Michael


>> Signed-off-by: Michael Kerrisk <mtk.manpages@...il.com>
>> ---
>>  kernel/sys.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/kernel/sys.c b/kernel/sys.c
>> index a8c9f5a..ea9c881 100644
>> --- a/kernel/sys.c
>> +++ b/kernel/sys.c
>> @@ -2210,9 +2210,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>>               up_write(&me->mm->mmap_sem);
>>               break;
>>       case PR_MPX_ENABLE_MANAGEMENT:
>> +             if (arg2 || arg3 || arg4 || arg5)
>> +                     return -EINVAL;
>>               error = MPX_ENABLE_MANAGEMENT(me);
>>               break;
>>       case PR_MPX_DISABLE_MANAGEMENT:
>> +             if (arg2 || arg3 || arg4 || arg5)
>> +                     return -EINVAL;
>>               error = MPX_DISABLE_MANAGEMENT(me);
>>               break;
>>       default:
>> --
>> 1.9.3
>
> --
> ak@...ux.intel.com -- Speaking for myself only



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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