Re: [PATCH v5 11/39] x86/mm: Update pte_modify for _PAGE_COW

Borislav Petkov
2023-02-10T13:57:25Z

On Thu, Feb 09, 2023 at 05:09:15PM +0000, Edgecombe, Rick P wrote:
> What do you think, can we leave it or give it a new name? Maybe
> pte_set_dirty() to be more like the x86-only pte_set_flags() family of
> functions?

I'd do this (ontop of yours, not built, not tested, etc). It is short
and sweet:

pte_mkdirty() set both dirty flags
pte_modifl() sets only _PAGE_DIRTY

No special helpers to lookup what they do, no nothing. Plain and simple.

---
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 7942eff2af50..8ba37380966c 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -392,19 +392,10 @@ static inline pte_t pte_mkexec(pte_t pte)
return pte_clear_flags(pte, _PAGE_NX);
}

-static inline pte_t __pte_mkdirty(pte_t pte, bool soft)
-{
- pteval_t dirty = _PAGE_DIRTY;
-
- if (soft)
- dirty |= _PAGE_SOFT_DIRTY;
-
- return pte_set_flags(pte, dirty);
-}
-
+/* Set _PAGE_SOFT_DIRTY for shadow stack pages. */
static inline pte_t pte_mkdirty(pte_t pte)
{
- return __pte_mkdirty(pte, true);
+ return pte_set_flags(pte, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
}

static inline pte_t pte_mkyoung(pte_t pte)
@@ -749,14 +740,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)

pte_result = __pte(val);

- /*
- * Dirty bit is not preserved above so it can be done
- * in a special way for the shadow stack case, where it
- * may need to set _PAGE_COW. __pte_mkdirty() will do this in
- * the case of shadow stack.
- */
if (pte_dirty(pte))
- pte_result = __pte_mkdirty(pte_result, false);
+ pte_result = pte_set_flags(pte_result, _PAGE_DIRTY);

return pte_result;
}

--
Regards/Gruss,
Boris.