linux-kernel - Re: [PATCH 18/20] arm64: ptrace: handle ptrace_request differently for aarch32 and ilp32

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Message-ID: <59522F8A.4010709@arm.com>
Date:   Tue, 27 Jun 2017 11:12:26 +0100
From:   James Morse <james.morse@....com>
To:     Yury Norov <ynorov@...iumnetworks.com>, zhouchengming1@...wei.com
CC:     Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Andrew Pinski <pinskia@...il.com>,
        Andrew Pinski <Andrew.Pinski@...iumnetworks.com>,
        Adam Borowski <kilobyte@...band.pl>,
        Chris Metcalf <cmetcalf@...hip.com>,
        Steve Ellcey <sellcey@...iumnetworks.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Ramana Radhakrishnan <ramana.gcc@...glemail.com>,
        Florian Weimer <fweimer@...hat.com>,
        Bamvor Zhangjian <bamvor.zhangjian@...wei.com>,
        Andreas Schwab <schwab@...e.de>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        schwidefsky@...ibm.com, broonie@...nel.org,
        Joseph Myers <joseph@...esourcery.com>,
        christoph.muellner@...obroma-systems.com, szabolcs.nagy@....com,
        klimov.linux@...il.com, Nathan_Lynch@...tor.com, agraf@...e.de,
        Prasun.Kapoor@...iumnetworks.com, geert@...ux-m68k.org,
        philipp.tomsich@...obroma-systems.com, manuel.montezelo@...il.com,
        linyongting@...wei.com, davem@...emloft.net,
        Bamvor Jian Zhang <bamvor.zhangjian@...aro.org>
Subject: Re: [PATCH 18/20] arm64: ptrace: handle ptrace_request differently
 for aarch32 and ilp32

Hi Yury, Zhou,

On 23/06/17 23:28, Yury Norov wrote:
> On Fri, Jun 23, 2017 at 06:03:37PM +0100, James Morse wrote:
>> Hi Yury,
>>
>> On 04/06/17 13:00, Yury Norov wrote:
>>> ILP32 has context-related structures different from both aarch32 and
>>> aarch64/lp64. In this patch compat_arch_ptrace() renamed to
>>> compat_a32_ptrace(), and compat_arch_ptrace() only makes choice between
>>> compat_a32_ptrace() and new compat_ilp32_ptrace() handler.
>>>
>>> compat_ilp32_ptrace() calls generic compat_ptrace_request() for all
>>> requests except PTRACE_GETSIGMASK and PTRACE_SETSIGMASK, which need
>>> special handling.
>>
>> Can you elaborate on this special handling?
>>
>> How come we don't need to wrap PTRACE_{G,S}ETSIGMASK for aarch32 compat?
>> >From kernel/signal32.c that uses compat_sigset_t too.
>>
>> It looks like aarch64, ilp32 and aarch32 all use the same size sigset_t,
>> so doesn't compat_ptrace_request() already do everything we need?
>>
>> ...
>>
>> Is this fixing an endian problem? If so, can we document it as such. Do we
>> already have the same bug for aarch32 compat?
> 
> Originally, the problem was found by Zhou Chengming: https://lkml.org/lkml/2016/6/27/18
> But I think you right, this is the fix for endian.
> 
> It lookd like aarch32 is buggy, but IIUC to confirm it, the BE arm64
> machine is needed. I use qemu and AFAIR it has no BE support.
> 
> Zhou, can you test it on your machine and if the bug will be reproduced,
> send the patch for aarch32?

I've reproduced this on big endian compat-aarch32: yes its broken. I will respin
Zhou's patch as a fix.


Thanks,

James