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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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