On Wed, 2018-07-11 at 11:29 +0200, Peter Zijlstra wrote: > On Tue, Jul 10, 2018 at 03:26:28PM -0700, Yu-cheng Yu wrote: > > > > There are three possible shadow stack PTE settings: > > > > Normal SHSTK PTE: (R/O + DIRTY_HW) > > SHSTK PTE COW'ed: (R/O + DIRTY_HW) > > SHSTK PTE shared as R/O data: (R/O + DIRTY_SW) > I count _2_ distinct states there. > > > > > Update can_follow_write_pte/pmd for the shadow stack. > So the below disallows can_follow_write when shstk && _PAGE_DIRTY_SW, > but this here Changelog doesn't explain why. Doesn't even get close. Can we add the following to the log: When a SHSTK PTE is shared, it is (R/O + DIRTY_SW); otherwise it is (R/O + DIRTY_HW). When we (FOLL_WRITE | FOLL_FORCE) on a SHSTK PTE, the following must be true: - It has been COW'ed at least once (FOLL_COW is set); - It still is not shared, i.e. PTE is (R/O + DIRTY_HW); > > Also, the code is a right mess :/ Can't we try harder to not let this > shadow stack stuff escape arch code. We either check here if the VMA is SHSTK mapping or move the logic to pte_dirty(). The latter would be less obvious. Or can we create a can_follow_write_shstk_pte()? Yu-cheng
