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    SubjectRe: [RFC PATCH v2 13/27] mm: Handle shadow stack page fault
    On Tue, Jul 10, 2018 at 04:06:25PM -0700, Dave Hansen wrote:
    > On 07/10/2018 03:26 PM, Yu-cheng Yu wrote:
    > > + if (is_shstk_mapping(vma->vm_flags))
    > > + entry = pte_mkdirty_shstk(entry);
    > > + else
    > > + entry = pte_mkdirty(entry);
    > > +
    > > + entry = maybe_mkwrite(entry, vma);
    > > if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
    > > update_mmu_cache(vma, vmf->address, vmf->pte);
    > > pte_unmap_unlock(vmf->pte, vmf->ptl);
    > > @@ -2526,7 +2532,11 @@ static int wp_page_copy(struct vm_fault *vmf)
    > > }
    > > flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
    > > entry = mk_pte(new_page, vma->vm_page_prot);
    > > - entry = maybe_mkwrite(pte_mkdirty(entry), vma);
    > > + if (is_shstk_mapping(vma->vm_flags))
    > > + entry = pte_mkdirty_shstk(entry);
    > > + else
    > > + entry = pte_mkdirty(entry);
    > > + entry = maybe_mkwrite(entry, vma);
    >
    > Do we want to lift this hunk of code and put it elsewhere? Maybe:
    >
    > entry = pte_set_vma_features(entry, vma);
    >
    > and then:
    >
    > pte_t pte_set_vma_features(pte_t entry, struct vm_area_struct)
    > {
    > /*
    > * Shadow stack PTEs are always dirty and always
    > * writable. They have a different encoding for
    > * this than normal PTEs, though.
    > */
    > if (is_shstk_mapping(vma->vm_flags))
    > entry = pte_mkdirty_shstk(entry);
    > else
    > entry = pte_mkdirty(entry);
    >
    > entry = maybe_mkwrite(entry, vma);
    >
    > return entry;
    > }

    Yes, that wants a helper like that. Not sold on the name, but whatever.

    Is there any way we can hide all the shadow stack magic in arch code?

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