On 08/04/2018 02:38 PM, Andy Lutomirski wrote: > On Thu, Aug 2, 2018 at 3:58 PM, Dave Hansen <dave.han...@linux.intel.com> > wrote: >> This otherwise unused alias mapping of the holes will, by default >> keep the Global bit, be mapped out to userspace, and be >> vulnerable to Meltdown. >> >> Remove the alias mapping of these pages entirely. This is likely >> to fracture the 2M page mapping the kernel image near these areas, >> but this should affect a minority of the area. ... > > I like this patch, and I tend to think we should (eventually) enable > it regardless of PTI. Cleaning up the memory map is generally a good > thing. > > Also, just to make sure I fully understand: the kernel text is aliased > in both the direct map and the high map, right?
Yes. I don't think the double mapping was because of anything that we really intentionally designed, though. I think it was just easiest to leave it in place and it didn't hurt anything. > This means that we should be able to make the high kernel mapping > have proper RO permissions very early without breaking text_poke() at > the minor cost of needing to force a serializing instruction at the > end of each big block of text pokes. I think this would be > worthwhile, although I suspect we'll uncover *tons* of bugs in the > process. Yeah, this could easily happen much earlier.
