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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Cyrill Gorcunov' <gorcunov@gmail.com>,
        Joel Savitz <jsavitz@redhat.com>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Thomas Gleixner" <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        "Masami Hiramatsu" <mhiramat@kernel.org>,
        Waiman Long <longman@redhat.com>,
        "Mauro Carvalho Chehab" <mchehab+samsung@kernel.org>,
        Kristina Martsenko <kristina.martsenko@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        YueHaibing <yuehaibing@huawei.com>,
        Micah Morton <mortonm@chromium.org>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Jann Horn <jannh@google.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Rafael Aquini <aquini@redhat.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Yury Norov <norov.maillist@gmail.com>
Subject: RE: [PATCH v2 1/2] kernel/sys: add PR_GET_TASK_SIZE option to
 prctl(2)
Thread-Topic: [PATCH v2 1/2] kernel/sys: add PR_GET_TASK_SIZE option to
 prctl(2)
Thread-Index: AQHVAYqqcxRhj7bMTkeIUrrm9JebiKZZRD3w
Date:   Fri, 3 May 2019 11:31:40 +0000
Message-ID: <6cf43408000149d98cc1683943c436cb@AcuMS.aculab.com>
References: <1556830342-32307-1-git-send-email-jsavitz@redhat.com>
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 <20190502210922.GF2488@uranus.lan>
 <CAL1p7m6eC3-99oFEyp0F1xn7qN4Vx+s-kHQXh14cMUWoVFqbWw@mail.gmail.com>
 <20190503083149.GH2488@uranus.lan>
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From: Cyrill Gorcunov
> Sent: 03 May 2019 09:32
> On Thu, May 02, 2019 at 05:46:08PM -0400, Joel Savitz wrote:
> > > Won't be possible to use put_user here? Something like
> > >
> > > static int prctl_get_tasksize(unsigned long __user *uaddr)
> > > {
> > >         return put_user(TASK_SIZE, uaddr) ? -EFAULT : 0;
> > > }
> >
> > What would be the benefit of using put_user() over copy_to_user() in
> > this context?
> 
> It is a common pattern to use put_user with native types, where
> copy_to_user more biased for composed types transfer.

It also removes all the crappy code that checks whether the
kernel buffer is valid.

	David

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