diff mbox series

[v23,11/28] x86/mm: Update pte_modify for _PAGE_COW

Message ID 20210316151054.5405-12-yu-cheng.yu@intel.com (mailing list archive)
State New, archived
Headers show
Series Control-flow Enforcement: Shadow Stack | expand

Commit Message

Yu-cheng Yu March 16, 2021, 3:10 p.m. UTC 
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 | 37 ++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

Comments

Kirill A. Shutemov March 22, 2021, 11:31 a.m. UTC | #1 
On Tue, Mar 16, 2021 at 08:10:37AM -0700, Yu-cheng Yu wrote:
> 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>

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
diff mbox series

Patch

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 9c056d5815de..e1739f590ca6 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -799,6 +799,23 @@  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);
+
+	/*
+	 * Fix up potential shadow stack page flags because the RO, Dirty
+	 * PTE is special.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+		if (pte_dirty(pte)) {
+			pte = pte_mkclean(pte);
+			pte = pte_mkdirty(pte);
+		}
+	}
+	return pte_val(pte);
+}
+
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
 	pteval_t val = pte_val(pte), oldval = val;
@@ -809,16 +826,36 @@  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);
+
+	/*
+	 * Fix up potential shadow stack page flags because the RO, Dirty
+	 * PMD is special.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_SHSTK)) {
+		if (pmd_dirty(pmd)) {
+			pmd = pmd_mkclean(pmd);
+			pmd = pmd_mkdirty(pmd);
+		}
+	}
+	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);
 }