| Subject | Re: [RFC PATCH v2 16/27] mm: Modify can_follow_write_pte/pmd for shadow stack | From | Dave Hansen <> | Date | Tue, 10 Jul 2018 16:37:43 -0700 |
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On 07/10/2018 03:26 PM, 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) > > Update can_follow_write_pte/pmd for the shadow stack.
First of all, thanks for the excellent patch headers. It's nice to have that reference every time even though it's repeated.
> -static inline bool can_follow_write_pte(pte_t pte, unsigned int flags) > +static inline bool can_follow_write_pte(pte_t pte, unsigned int flags, > + bool shstk) > { > + bool pte_cowed = shstk ? is_shstk_pte(pte):pte_dirty(pte); > + > return pte_write(pte) || > - ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte)); > + ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_cowed); > }
Can we just pass the VMA in here? This use is OK-ish, but I generally detest true/false function arguments because you can't tell what they are when they show up without a named variable.
But... Why does this even matter? Your own example showed that all shadowstack PTEs have either DIRTY_HW or DIRTY_SW set, and pte_dirty() checks both.
That makes this check seem a bit superfluous.
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