Re: [PATCH 10/18] qla2xxx: prevent bounds-check bypass via speculative execution

Greg KH
2018-01-12T07:27:58Z

On Thu, Jan 11, 2018 at 02:15:12PM -0800, Dan Williams wrote:
> On Sat, Jan 6, 2018 at 1:03 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Fri, Jan 05, 2018 at 05:10:48PM -0800, Dan Williams wrote:
> >> Static analysis reports that 'handle' may be a user controlled value
> >> that is used as a data dependency to read 'sp' from the
> >> 'req->outstanding_cmds' array. In order to avoid potential leaks of
> >> kernel memory values, block speculative execution of the instruction
> >> stream that could issue reads based on an invalid value of 'sp'. In this
> >> case 'sp' is directly dereferenced later in the function.
> >
> > I'm pretty sure that 'handle' comes from the hardware, not from
> > userspace, from what I can tell here. If we want to start auditing
> > __iomem data sources, great! But that's a bigger task, and one I don't
> > think we are ready to tackle...
>
> I think it falls in the hygiene bucket of shutting off an array index
> from a source that could be under attacker control. Should we leave
> this one un-patched while we decide if we generally have a problem
> with trusting completion 'tags' from hardware? My vote is patch it for
> now.

Hah, if you are worried about "tags" from hardware, we have a lot more
auditing to do, right? I don't think anyone has looked into just basic
"bounds checking" for that type of information. For USB devices we have
_just_ started doing that over the past year, the odds of anyone looking
at PCI devices for this same problem is slim-to-none.

Again, here are my questions/objections right now to this series:
- How can we audit this stuff?
- How did you audit this stuff to find these usages?
- How do you know that this series fixes all of the issues?
- What exact tree/date did you run your audit against?
- How do you know that linux-next does not contain a boatload
more problems that we need to go back and fix after 4.16-rc1
is out?
- How can we prevent this type of pattern showing up again?
- How can we audit the data coming from hardware correctly?

I'm all for merging this series, but if anyone things that somehow the
whole problem is now "solved" in this area, they are sorely mistaken.

thanks,

greg k-h