Re: [PATCH 06/18] x86, barrier: stop speculation for failed access_ok

[Alan Cox]

On Fri, 5 Jan 2018 18:52:07 -0800
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Fri, Jan 5, 2018 at 5:10 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> > From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> >
> > 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