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

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Message-ID: <07438b1e94ff42a184adb7134a680069@AcuMS.aculab.com>
Date:   Thu, 29 Mar 2018 14:46:44 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Dominik Brodowski' <linux@...inikbrodowski.net>,
        Matthew Wilcox <willy@...radead.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "viro@...IV.linux.org.uk" <viro@...IV.linux.org.uk>,
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        Amir Goldstein <amir73il@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
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Subject: RE: [PATCH 000/109] remove in-kernel calls to syscalls

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

	David