On Thu, Jan 04, 2018 at 12:45:29AM +0100, Peter Zijlstra wrote: > On Wed, Jan 03, 2018 at 10:38:27PM +0000, Mark Rutland wrote: > > Under speculation, CPUs may mis-predict branches in bounds checks. Thus, > > memory accesses under a bounds check may be speculated even if the > > bounds check fails, providing a primitive for building a side channel. > > > > The EBPF map code has a number of such bounds-checks accesses in > > map_lookup_elem implementations. This patch modifies these to use the > > nospec helpers to inhibit such side channels. > > > > The JITted lookup_elem implementations remain potentially vulnerable, > > and are disabled (with JITted code falling back to the C > > implementations). > > Since this is now public, let me re-iterate that I don't particularly > like this approach. If you have to kill the JIT, could we please keep > that in the arch JIT implementation? Hopefully, killing the JIT is a temporary bodge. I agree that we want the arch backends to JIT safe sequences somehow; I just haven't figured out exactly what we need to do to make that happen. Thanks, Mark.
