From mboxrd@z Thu Jan  1 00:00:00 1970
Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date: Fri, 12 May 2017 09:00:12 +0200
From: Ingo Molnar <mingo@kernel.org>
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Subject: Re: [kernel-hardening] Re: [PATCH v9 1/4] syscalls: Verify address
 limit before returning to user-mode
List-Archive: <https://lore.kernel.org/kernel-hardening/>
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To: Andy Lutomirski <luto@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>, Greg KH <greg@kroah.com>, Thomas Garnier <thgarnie@google.com>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, Dave Hansen <dave.hansen@intel.com>, Arnd Bergmann <arnd@arndb.de>, Thomas Gleixner <tglx@linutronix.de>, David Howells <dhowells@redhat.com>, =?iso-8859-1?Q?Ren=E9?= Nyffenegger <mail@renenyffenegger.ch>, Andrew Morton <akpm@linux-foundation.org>, "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>, "Eric W . Biederman" <ebiederm@xmission.com>, Oleg Nesterov <oleg@redhat.com>, Pavel Tikhomirov <ptikhomirov@virtuozzo.com>, Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>, Paolo Bonzini <pbonzini@redhat.com>, Rik van Riel <riel@redhat.com>, Kees Cook <keescook@chromium.org>, Josh Poimboeuf <jpoimboe@redhat.com>, Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Christian Borntraeger <borntraeger@de.ibm.com>, Russell King <linux@armlinux.org.uk>, Will Deacon <will.deacon@arm.com>, Catalin Marinas <catalin.marinas@arm.com>, Mark Rutland <mark.rutland@arm.com>, James Morse <james.morse@arm.com>, linux-s390 <linux-s390@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, Linux API <linux-api@vger.kernel.org>, the arch/x86 maintainers <x86@kernel.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>, Kernel Hardening <kernel-hardening@lists.openwall.com>, Linus Torvalds <torvalds@linux-foundation.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>
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* Andy Lutomirski <luto@kernel.org> wrote:

> On Tue, May 9, 2017 at 1:56 AM, Christoph Hellwig <hch@infradead.org> wrote:
> > 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.
> 
> How about trying to remove all of them?  If we could actually get rid
> of all of them, we could drop the arch support, and we'd get faster,
> simpler, shorter uaccess code throughout the kernel.

I'm all for that!

Thanks,

	Ingo