linux-kernel - Re: [RFC PATCH 01/11] prctl: Support movement of arch prctls out of common code

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Date:   Mon, 21 May 2018 19:28:26 +0100
From:   Will Deacon <will.deacon@....com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        James Hogan <jhogan@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Matt Turner <mattst88@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Richard Henderson <rth@...ddle.net>,
        Rich Felker <dalias@...c.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>, x86@...nel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>
Subject: Re: [RFC PATCH 01/11] prctl: Support movement of arch prctls out of
 common code

Hi Dave,

On Mon, May 14, 2018 at 06:14:17PM +0100, Dave Martin wrote:
> The core framework for the prctl() syscall is unloved and looking
> rather crusty these days.  It also relies on defining ancillary
> boilerplate macros for each prctl() in order to control conditional
> compilation of the different prctl calls.  We have better ways to
> do this now, using Kconfig.
> 
> This patch defines a new arch hook arch_syscall().  Architectures
> that implemement arch-specific syscalls can now select
> HAVE_ARCH_SYSCALL in their Kconfig and define this function
> appropriately.
> 
> The core prctl() implementation now matches option against the list
> of common or legacy prctls, deferring to prctl_arch() if an
> unrecognised option is encountered.
> 
> (arch_prctl() would have been a nicer name, but it conflicts with the
> pre-existing syscall of the same name on x86, particularly in the um
> code.)
> 
> No functional change.

[...]

> diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
> index af5f8c2..c911ff0 100644
> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -1,6 +1,6 @@
>  /* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> -#ifndef _LINUX_PRCTL_H
> -#define _LINUX_PRCTL_H
> +#ifndef _UAPI_LINUX_PRCTL_H
> +#define _UAPI_LINUX_PRCTL_H

Is it safe to rename this #define, or is there a possibility that userspace
could be using it for something and relying on it not changing?

Other than that:

Acked-by: Will Deacon <will.deacon@....com>

Will