From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Subject: Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode
Date: Tue, 9 May 2017 01:56:59 -0700
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To: Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Cc: Greg KH <greg-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>, Thomas Garnier <thgarnie-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>, Martin Schwidefsky <schwidefsky-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, Heiko Carstens <heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, Dave Hansen <dave.hansen-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, =?iso-8859-1?Q?Ren=E9?= Nyffenegger <mail-gLCNRsNSrVdVZEhyV+6z5nIPMjoJpjVV@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, "Paul E . McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, "Eric W . Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>, Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Pavel Tikhomirov <ptikhomirov-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, "H . Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>, Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Paolo Bonzini <pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Rik van Riel <riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Kees
List-Id: linux-api@vger.kernel.org

On Tue, May 09, 2017 at 08:45:22AM +0200, Ingo Molnar wrote:
> We only have ~115 code blocks in the kernel that set/restore KERNEL_DS, it would 
> be a pity to add a runtime check to every system call ...

I think we should simply strive to remove all of them that aren't
in core scheduler / arch code.  Basically evetyytime we do the

	oldfs = get_fs();
	set_fs(KERNEL_DS); 
	..
	set_fs(oldfs);

trick we're doing something wrong, and there should always be better
ways to archive it.  E.g. using iov_iter with a ITER_KVEC type
consistently would already remove most of them.