Messages in this thread | | | Date | Tue, 27 Dec 2022 12:42:12 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v4 11/39] x86/mm: Update pte_modify for _PAGE_COW |
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On Fri, Dec 02, 2022 at 04:35:38PM -0800, Rick Edgecombe wrote: > static inline pte_t pte_modify(pte_t pte, pgprot_t newprot) > { > + pteval_t _page_chg_mask_no_dirty = _PAGE_CHG_MASK & ~_PAGE_DIRTY; > pteval_t val = pte_val(pte), oldval = val; > + pte_t pte_result; > > /* > * Chop off the NX bit (if present), and add the NX portion of > * the newprot (if present): > */ > - val &= _PAGE_CHG_MASK; > - val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK; > + val &= _page_chg_mask_no_dirty; > + val |= check_pgprot(newprot) & ~_page_chg_mask_no_dirty; > val = flip_protnone_guard(oldval, val, PTE_PFN_MASK); > - return __pte(val); > + > + pte_result = __pte(val); > + > + /* > + * Dirty bit is not preserved above so it can be done
Just for my own understanding: are you saying here that flip_protnone_guard() might end up setting _PAGE_DIRTY in val...
> + * in a special way for the shadow stack case, where it > + * needs to set _PAGE_COW. pte_mkcow() will do this in > + * the case of shadow stack. > + */ > + if (pte_dirty(pte_result)) > + pte_result = pte_mkcow(pte_result);
... and in that case we need to turn it into a _PAGE_COW setting?
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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