From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Subject: Re: [PATCH 06/18] x86, barrier: stop speculation for failed
 access_ok
Date: Sat, 6 Jan 2018 12:32:42 +0000
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-arch@vger.kernel.org, Andi Kleen <ak@linux.intel.com>, Arnd Bergmann <arnd@arndb.de>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Peter Zijlstra <peterz@infradead.org>, Network Development <netdev@vger.kernel.org>, the arch/x86 maintainers <x86@kernel.org>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>

On Fri, 5 Jan 2018 18:52:07 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Fri, Jan 5, 2018 at 5:10 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> > From: Andi Kleen <ak@linux.intel.com>
> >
> > When access_ok fails we should always stop speculating.
> > Add the required barriers to the x86 access_ok macro.  
> 
> Honestly, this seems completely bogus.

Also for x86-64 if we are trusting that an AND with a constant won't get
speculated into something else surely we can just and the address with ~(1
<< 63) before copying from/to user space ? The user will then just
speculatively steal their own memory.

Alan