linux-kernel - Re: [PATCH v2 1/2] kernel/sys: add PR_GET_TASK

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Message-ID: <20190503083149.GH2488@uranus.lan>
Date:   Fri, 3 May 2019 11:31:49 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Joel Savitz <jsavitz@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Kristina Martsenko <kristina.martsenko@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Micah Morton <mortonm@...omium.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Jann Horn <jannh@...gle.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Rafael Aquini <aquini@...hat.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Yury Norov <norov.maillist@...il.com>
Subject: Re: [PATCH v2 1/2] kernel/sys: add PR_GET_TASK_SIZE option to
 prctl(2)

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.