On Sat, Apr 08, 2017 at 08:20:03AM -0700, Andy Lutomirski wrote: > On Sat, Apr 8, 2017 at 12:33 AM, Daniel Micay <danielmi...@gmail.com> wrote: > > The > > submitted code is aimed at rare writes to globals, but this feature is > > more than that and design decisions shouldn't be based on just the > > short term. > > Then, if you disagree with a proposed design, *explain why* in a > standalone manner. Say what future uses a different design would > have. > > > I actually care a lot more about 64-bit ARM support than I do x86, but > > using a portable API for pax_open_kernel (for the simple uses at > > least) is separate from choosing the underlying implementation. There > > might not be a great way to do it on the architectures I care about > > but that doesn't need to hinder x86. It's really not that much code... > > A weaker/slower implementation for x86 also encourages the same > > elsewhere. > > No one has explained how CR0.WP is weaker or slower than my proposal. > Here's what I'm proposing: > > At boot, choose a random address A. Create an mm_struct that has a > single VMA starting at A that represents the kernel's rarely-written > section. Compute O = (A - VA of rarely-written section). To do a > rare write, use_mm() the mm, write to (VA + O), then unuse_mm(). > > This should work on any arch that has an MMU that allows this type of > aliasing and that doesn't have PA-based protections on the > rarely-written section.
Modulo randomization, that sounds exactly like what I had envisaged [1], so that makes sense to me. Thanks, Mark. [1] http://www.openwall.com/lists/kernel-hardening/2016/11/18/3
