[PATCH v7 20/41] x86/mm: Teach pte_mkwrite() about stack memory

[Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>]

If a VMA has the VM_SHADOW_STACK flag, it is shadow stack memory. So
when it is made writable with pte_mkwrite(), it should create shadow
stack memory, not conventionally writable memory. Now that pte_mkwrite()
takes a VMA, and places where shadow stack memory might be created pass
one, pte_mkwrite() can know when it should do this.

So make pte_mkwrite() create shadow stack memory when the VMA has the
VM_SHADOW_STACK flag. Do the same thing for pmd_mkwrite().

This requires referencing VM_SHADOW_STACK in these functions, which are
currently defined in pgtable.h, however mm.h (where VM_SHADOW_STACK is
located) can't be pulled in without causing problems for files that
reference pgtable.h. So also move pte/pmd_mkwrite() into pgtable.c, where
they can safely reference VM_SHADOW_STACK.

Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Tested-by: John Allen <john.allen@xxxxxxx>
Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>

---
v6:
 - New patch
---
 arch/x86/include/asm/pgtable.h | 20 ++------------------
 arch/x86/mm/pgtable.c          | 26 ++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 18 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 05dfdbdf96b4..d81e7ec27507 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -456,15 +456,7 @@ static inline pte_t pte_mkwrite_kernel(pte_t pte)
 
 struct vm_area_struct;
 
-static inline pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma)
-{
-	pte = pte_mkwrite_kernel(pte);
-
-	if (pte_dirty(pte))
-		pte = pte_clear_saveddirty(pte);
-
-	return pte;
-}
+pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma);
 
 static inline pte_t pte_mkhuge(pte_t pte)
 {
@@ -601,15 +593,7 @@ static inline pmd_t pmd_mkyoung(pmd_t pmd)
 	return pmd_set_flags(pmd, _PAGE_ACCESSED);
 }
 
-static inline pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
-{
-	pmd = pmd_set_flags(pmd, _PAGE_RW);
-
-	if (pmd_dirty(pmd))
-		pmd = pmd_clear_saveddirty(pmd);
-
-	return pmd;
-}
+pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
 
 static inline pud_t pud_set_flags(pud_t pud, pudval_t set)
 {
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index e4f499eb0f29..98856bcc8102 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -880,3 +880,29 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
 
 #endif /* CONFIG_X86_64 */
 #endif	/* CONFIG_HAVE_ARCH_HUGE_VMAP */
+
+pte_t pte_mkwrite(pte_t pte, struct vm_area_struct *vma)
+{
+	if (vma->vm_flags & VM_SHADOW_STACK)
+		return pte_mkwrite_shstk(pte);
+
+	pte = pte_mkwrite_kernel(pte);
+
+	if (pte_dirty(pte))
+		pte = pte_clear_saveddirty(pte);
+
+	return pte;
+}
+
+pmd_t pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
+{
+	if (vma->vm_flags & VM_SHADOW_STACK)
+		return pmd_mkwrite_shstk(pmd);
+
+	pmd = pmd_set_flags(pmd, _PAGE_RW);
+
+	if (pmd_dirty(pmd))
+		pmd = pmd_clear_saveddirty(pmd);
+
+	return pmd;
+}
-- 
2.17.1