Re: [PATCH v8 15/27] mm: Handle shadow stack page fault

Andy Lutomirski
2019-08-13T22:55:07Z

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?

--Andy