On Thu, Dec 7, 2017 at 4:43 AM, Borislav Petkov <b...@alien8.de> wrote: > On Wed, Dec 06, 2017 at 11:22:21PM -0800, Andy Lutomirski wrote: >> I think I like this approach. I also think it might be nice to move the >> whole cpu_entry_area into this new pgd range so that we can stop mucking >> around with the fixmap. > > Yeah, and also, I don't like the idea of sacrificing a whole PGD > only for the LDT crap which is optional, even. Frankly - and this > is just me - I'd make CONFIG_KERNEL_PAGE_TABLE_ISOLATION xor > CONFIG_MODIFY_LDT_SYSCALL and don't give a rat's *ss about the LDT.
The PGD sacrifice doesn't bother me. Putting a writable LDT map at a constant address does bother me. We could probably get away with RO if we trapped and handled the nasty faults, but that could be very problematic. The version here: https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/pti&id=a74d1009ac72a1f04ec5bcd338a4bdbe170ab776 actually seems to work.
