linux-kernel - Re: [PATCH] [RFC] syscalls,x86: Add execveat() system call (v2)

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Date:	Thu, 2 Aug 2012 10:14:53 +0100
From:	Meredydd Luff <meredydd@...atehouse.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Kees Cook <keescook@...omium.org>,
	Ingo Molnar <mingo@...hat.com>, Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH] [RFC] syscalls,x86: Add execveat() system call (v2)

On Thu, Aug 2, 2012 at 7:55 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
>> This means you need an x32 version of the function -- execve
>> unfortunately is one of the few system calls which require a special x32
>> version (although it's a simple wrapper around sys32_execve).  See
>> sys_x32_execve.
>
> I *really* strongly object to doing that thing before we sanitize the
> situation with sys_execve().

"That thing" = "creating an x32 entry stub", or "merging execveat() at all"?

(snip)
> The thing is, there's essentially no reason to have more than one
> implementation.  What they are (badly) doing is "we need to find
> pt_regs to pass to do_execve(), the thing we are after has to be near
> our stack frame, so let's try to get to it that way".

Hang on...it's not just sys_execve that fits that description, is it?
You seem to be describing every call that needs a pt_regs parameter,
which at a glance is anything with a stub_ or PTREGSCALL in
arch/x86/kernel/entry_{32,64}.S. That's: clone, fork, vfork,
sigaltstack, iopl, execve, sigreturn, rt_sigreturn, vm86, vm86old.
Most of those are handled by a common PTREGSCALL macro, but there are
a few that get special treatment (different set on each arch - on
x86-64 it's execve and rt_sigreturn ; on i386 it's just clone).

Is there's something special about execve in particular, or do you
want to overhaul all the ptregscalls?

Meredydd
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