On Tue, 2019-08-13 at 15:55 -0700, Andy Lutomirski wrote: > On Tue, Aug 13, 2019 at 2:02 PM Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote: > > > > When a task does fork(), its shadow stack (SHSTK) must be duplicated > > for the child. This patch implements a flow similar to copy-on-write > > of an anonymous page, but for SHSTK. > > > > A SHSTK PTE must be RO and dirty. This dirty bit requirement is used > > to effect the copying. In copy_one_pte(), clear the dirty bit from a > > SHSTK PTE to cause a page fault upon the next SHSTK access. At that > > time, fix the PTE and copy/re-use the page. > > Is using VM_SHSTK and special-casing all of this really better than > using a special mapping or other pseudo-file-backed VMA and putting > all the magic in the vm_operations? A special mapping is cleaner. However, we also need to exclude normal [RO + dirty] pages from shadow stack. Yu-cheng
