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

[Dominik Brodowski <linux@dominikbrodowski.net>]

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