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In-Reply-To: <20200730114842.GH3703480@smile.fi.intel.com>
From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 30 Jul 2020 15:49:08 +0200
Message-ID: <CAK8P3a2L1yK=XuS5vGj-einsNKU99ZdX53Ao5TUfc7_WU-LOYA@mail.gmail.com>
Subject: Re: [Linux-kernel-mentees] [PATCH v3] media/v4l2-core: Fix
 kernel-infoleak in video_put_user()
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     Bartosz Golaszewski <brgl@bgdev.pl>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Peilin Ye <yepeilin.cs@gmail.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Vandana BN <bnvandana@gmail.com>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        =?UTF-8?Q?Niklas_S=C3=B6derlund?= 
        <niklas.soderlund+renesas@ragnatech.se>,
        linux-kernel-mentees@lists.linuxfoundation.org,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Thu, Jul 30, 2020 at 1:48 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
> On Thu, Jul 30, 2020 at 11:18:04AM +0200, Arnd Bergmann wrote:
> > The in_ia32_syscall() check should be completely reliable in telling whether
> > we are called from read() by an ia32 task or not, and we use the same
> > logic for input_event, which has a similar problem (on all compat architectures,
> > not just x86).
>
> By the way any reason why we have to have in_ia32_syscall() instead of
> in_compat_syscall()?

x86 is the only architecture that has different struct alignment between 32-bit
and 64-bit processes, so others don't have this particular problem. On top of
that, x86 also has two different 32-bit ABIs and only one of them needs the
workaround, while the other (x32) uses the same struct layout as x86-64 and
must use the normal code path.

       Arnd