linux-kernel - Re: [PATCH] x86, vsyscall: Fix build warning in vsyscall

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Message-ID: <BANLkTi=yEo9fcXW8SqUCtSOag7Mn_+Ni9Q@mail.gmail.com>
Date:	Sun, 12 Jun 2011 11:12:37 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Andrew Lutomirski <luto@....edu>
Cc:	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86, vsyscall: Fix build warning in vsyscall_64.c

On Sat, Jun 11, 2011 at 5:01 PM, Andrew Lutomirski <luto@....edu> wrote:
> On Sat, Jun 11, 2011 at 3:31 AM, Rakib Mullick <rakib.mullick@...il.com> wrote:
>> Due to commit 5cec93c216db77 (x86-64: Emulate legacy vsyscalls), we get the following warning:
>>
>>   arch/x86/kernel/vsyscall_64.c: In function ‘do_emulate_vsyscall’:
>>   arch/x86/kernel/vsyscall_64.c:111:7: warning: ‘ret’ may be used uninitialized in this function
>
> What's the code path that uses ret without initializing it?
>
In case of, vsyscall_nr is default it might gets uninitialized. And
current code already treats it as a bug.

>> -       if (ret == -EFAULT) {
>> +       if (ret == -EFAULT || ret == -EINVAL) {
>>                /*
>>                 * Bad news -- userspace fed a bad pointer to a vsyscall.
>>                 *
>
> EINVAL doesn't seem like grounds to fault.  (I'm not sure how to get
> EINVAL from time, gettimeofday, or getcpu, but in case there is, we
> should return it back to userspace.)
>
If ret = EINVAL, then it means vsyscall_nr doesn't any of
gettimeofday, time or getcpu. So, I grounds it into fault. In case of
gettimeofday, EINVAL may gets return. But, maybe not in case of time
or getcpu. So, maybe we need to check EINVAL in case of gettimeofday
and maybe should separate EINVAL and EFAULT.

Thanks,
Rakib
> --Andy
>
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