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Re: [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test

Started byIngo Molnar <mingo@kernel.org>
First post2016-05-16 16:00 +0200
Last post2016-05-16 20:30 +0200
Articles 3 — 3 participants

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  Re: [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test Ingo Molnar <mingo@kernel.org> - 2016-05-16 16:00 +0200
    Re: [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test Dmitry Safonov <dsafonov@virtuozzo.com> - 2016-05-16 18:50 +0200
      Re: [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test Andy Lutomirski <luto@amacapital.net> - 2016-05-16 20:30 +0200

#1401512 — Re: [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test

FromIngo Molnar <mingo@kernel.org>
Date2016-05-16 16:00 +0200
SubjectRe: [PATCHv8 resend 2/2] selftest/x86: add mremap vdso test
Message-ID<rzrdU-7Kg-29@gated-at.bofh.it>
* Dmitry Safonov <dsafonov@virtuozzo.com> wrote:

> Should print on success:
> [root@localhost ~]# ./test_mremap_vdso_32
> 	AT_SYSINFO_EHDR is 0xf773f000
> [NOTE]	Moving vDSO: [f773f000, f7740000] -> [a000000, a001000]
> [OK]
> Or segfault if landing was bad (before patches):
> [root@localhost ~]# ./test_mremap_vdso_32
> 	AT_SYSINFO_EHDR is 0xf774f000
> [NOTE]	Moving vDSO: [f774f000, f7750000] -> [a000000, a001000]
> Segmentation fault (core dumped)

Can the segfault be caught and recovered from, to print a proper failure message?

Thanks,

	Ingo

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#1401631

FromDmitry Safonov <dsafonov@virtuozzo.com>
Date2016-05-16 18:50 +0200
Message-ID<rztSq-10v-23@gated-at.bofh.it>
In reply to#1401512
On 05/16/2016 04:54 PM, Ingo Molnar wrote:
>
> * Dmitry Safonov <dsafonov@virtuozzo.com> wrote:
>
>> Should print on success:
>> [root@localhost ~]# ./test_mremap_vdso_32
>> 	AT_SYSINFO_EHDR is 0xf773f000
>> [NOTE]	Moving vDSO: [f773f000, f7740000] -> [a000000, a001000]
>> [OK]
>> Or segfault if landing was bad (before patches):
>> [root@localhost ~]# ./test_mremap_vdso_32
>> 	AT_SYSINFO_EHDR is 0xf774f000
>> [NOTE]	Moving vDSO: [f774f000, f7750000] -> [a000000, a001000]
>> Segmentation fault (core dumped)
>
> Can the segfault be caught and recovered from, to print a proper failure message?

Will add segfault handler, thanks.

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#1401685

FromAndy Lutomirski <luto@amacapital.net>
Date2016-05-16 20:30 +0200
Message-ID<rzvrh-25A-17@gated-at.bofh.it>
In reply to#1401631
On Mon, May 16, 2016 at 9:24 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote:
> On 05/16/2016 04:54 PM, Ingo Molnar wrote:
>>
>>
>> * Dmitry Safonov <dsafonov@virtuozzo.com> wrote:
>>
>>> Should print on success:
>>> [root@localhost ~]# ./test_mremap_vdso_32
>>>         AT_SYSINFO_EHDR is 0xf773f000
>>> [NOTE]  Moving vDSO: [f773f000, f7740000] -> [a000000, a001000]
>>> [OK]
>>> Or segfault if landing was bad (before patches):
>>> [root@localhost ~]# ./test_mremap_vdso_32
>>>         AT_SYSINFO_EHDR is 0xf774f000
>>> [NOTE]  Moving vDSO: [f774f000, f7750000] -> [a000000, a001000]
>>> Segmentation fault (core dumped)
>>
>>
>> Can the segfault be caught and recovered from, to print a proper failure
>> message?
>
>
> Will add segfault handler, thanks.
>

It may be more complicated that that.  Glibc is likely to explode if
this happens, and the headers are sufficiently screwed up that it's
awkward to bypass glibc and call rt_sigaction directly.  I have a test
that does the latter, though, so it's at least possible, but I'm
unconvinced it's worth it just for an error message.

-- 
Andy Lutomirski
AMA Capital Management, LLC

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