On 8/14/19 9:27 AM, Yu-cheng Yu wrote: > 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. I don't understand what you are saying. Are you saying that we need this VM_SHSTK flag in order to exclude RO+HW-Dirty pages from being created in non-shadow-stack VMAs?
