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

Dan Williams
2018-01-11T22:15:13Z

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.