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

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Message-ID: <20180329145526.GA1414@isilmar-4.linta.de>
Date:   Thu, 29 Mar 2018 16:55:26 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Matthew Wilcox <willy@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "viro@...IV.linux.org.uk" <viro@...IV.linux.org.uk>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "hmclauchlan@...com" <hmclauchlan@...com>,
        "tautschn@...zon.co.uk" <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" <kexec@...ts.infradead.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
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        "Luis R . Rodriguez" <mcgrof@...nel.org>,
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        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "user-mode-linux-devel@...ts.sourceforge.net" 
        <user-mode-linux-devel@...ts.sourceforge.net>,
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Subject: Re: [PATCH 000/109] remove in-kernel calls to syscalls

On Thu, Mar 29, 2018 at 02:46:44PM +0000, David Laight wrote:
> From: Dominik Brodowski
> > Sent: 29 March 2018 15:42
> > 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.
> 
> Should be pretty easy to ensure the prototypes aren't in any normal header.

That's exactly why the compile will fail.

> Renaming the global symbols (to not match the function name) will make it
> much harder to call them as well.

That still depends on the exact design of the patchset, which is still under
review.

Thanks,
	Dominik