netdev - Re: [PATCH 000/109] remove in-kernel calls to syscalls

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Message-ID: <20180329144209.GA25559@isilmar-4.linta.de>
Date:   Thu, 29 Mar 2018 16:42:09 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, viro@...IV.linux.org.uk,
        torvalds@...ux-foundation.org, arnd@...db.de,
        linux-arch@...r.kernel.org, hmclauchlan@...com,
        tautschn@...zon.co.uk, Amir Goldstein <amir73il@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        "David S . Miller" <davem@...emloft.net>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        Jaswinder Singh <jaswinder@...radead.org>,
        Jeff Dike <jdike@...toit.com>, Jiri Slaby <jslaby@...e.com>,
        kexec@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org,
        "Luis R . Rodriguez" <mcgrof@...nel.org>, netdev@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        user-mode-linux-devel@...ts.sourceforge.net, x86@...nel.org
Subject: Re: [PATCH 000/109] remove in-kernel calls to syscalls

On Thu, Mar 29, 2018 at 07:20:27AM -0700, Matthew Wilcox wrote:
> On Thu, Mar 29, 2018 at 01:22:37PM +0200, Dominik Brodowski wrote:
> > At least on 64-bit x86, it will likely be a hard requirement from v4.17
> > onwards to not call system call functions in the kernel: It is better to
> > use use a different calling convention for system calls there, where 
> > struct pt_regs is decoded on-the-fly in a syscall wrapper which then hands
> > processing over to the actual syscall function. This means that only those
> > parameters which are actually needed for a specific syscall are passed on
> > during syscall entry, instead of filling in six CPU registers with random
> > user space content all the time (which may cause serious trouble down the
> > call chain).[*]
> 
> How do we stop new ones from springing up?  Some kind of linker trick
> like was used to, er, "dissuade" people from using gets()?

Once the patches which modify the syscall calling convention are merged,
it won't compile on 64-bit x86, but bark loudly. That should frighten anyone.
Meow.

Thanks,
	Dominik