[PATCH v19 10/25] x86/mm: Update pte_modify for _PAGE_COW

Yu-cheng Yu
2021-02-03T22:57:10Z

The read-only and Dirty PTE has been used to indicate copy-on-write pages.
However, newer x86 processors also regard a read-only and Dirty PTE as a
shadow stack page. In order to separate the two, the software-defined
_PAGE_COW is created to replace _PAGE_DIRTY for the copy-on-write case, and
pte_*() are updated.

Pte_modify() changes a PTE to 'newprot', but it doesn't use the pte_*().
Introduce fixup_dirty_pte(), which sets a dirty PTE, based on _PAGE_RW,
to either _PAGE_DIRTY or _PAGE_COW.

Apply the same changes to pmd_modify().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/include/asm/pgtable.h | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 4b0ec61510dc..4a7fd3e5b7df 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -726,6 +726,21 @@ static inline pmd_t pmd_mkinvalid(pmd_t pmd)

static inline u64 flip_protnone_guard(u64 oldval, u64 val, u64 mask);

+static inline pteval_t fixup_dirty_pte(pteval_t pteval)
+{
+ pte_t pte = __pte(pteval);
+
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK) && pte_dirty(pte)) {
+ pte = pte_mkclean(pte);
+
+ if (pte_flags(pte) & _PAGE_RW)
+ pte = pte_set_flags(pte, _PAGE_DIRTY);
+ else
+ pte = pte_set_flags(pte, _PAGE_COW);
+ }
+ return pte_val(pte);
+}
+
static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
{
pteval_t val = pte_val(pte), oldval = val;
@@ -736,16 +751,34 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
*/
val &= _PAGE_CHG_MASK;
val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK;
+ val = fixup_dirty_pte(val);
val = flip_protnone_guard(oldval, val, PTE_PFN_MASK);
return __pte(val);
}

+static inline int pmd_write(pmd_t pmd);
+static inline pmdval_t fixup_dirty_pmd(pmdval_t pmdval)
+{
+ pmd_t pmd = __pmd(pmdval);
+
+ if (cpu_feature_enabled(X86_FEATURE_SHSTK) && pmd_dirty(pmd)) {
+ pmd = pmd_mkclean(pmd);
+
+ if (pmd_flags(pmd) & _PAGE_RW)
+ pmd = pmd_set_flags(pmd, _PAGE_DIRTY);
+ else
+ pmd = pmd_set_flags(pmd, _PAGE_COW);
+ }
+ return pmd_val(pmd);
+}
+
static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
{
pmdval_t val = pmd_val(pmd), oldval = val;

val &= _HPAGE_CHG_MASK;
val |= check_pgprot(newprot) & ~_HPAGE_CHG_MASK;
+ val = fixup_dirty_pmd(val);
val = flip_protnone_guard(oldval, val, PHYSICAL_PMD_PAGE_MASK);
return __pmd(val);
}
--
2.21.0