Messages in this thread | | | Subject | Re: [PATCH v8 15/27] mm: Handle shadow stack page fault | From | Yu-cheng Yu <> | Date | Wed, 14 Aug 2019 09:27:21 -0700 |
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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@intel.com> 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
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