[v24,16/30] mm: Fixup places that call pte_mkwrite() directly

Commit Message

Yu-cheng Yu April 1, 2021, 10:10 p.m. UTC

When serving a page fault, maybe_mkwrite() makes a PTE writable if it is in
a writable vma.  A shadow stack vma is writable, but its PTEs need
_PAGE_DIRTY to be set to become writable.  For this reason, maybe_mkwrite()
has been updated.

There are a few places that call pte_mkwrite() directly, but have the
same result as from maybe_mkwrite().  These sites need to be updated for
shadow stack as well.  Thus, change them to maybe_mkwrite():

- do_anonymous_page() and migrate_vma_insert_page() check VM_WRITE directly
  and call pte_mkwrite(), which is the same as maybe_mkwrite().  Change
  them to maybe_mkwrite().

- In do_numa_page(), if the numa entry was writable, then pte_mkwrite()
  is called directly.  Fix it by doing maybe_mkwrite().

- In change_pte_range(), pte_mkwrite() is called directly.  Replace it with
  maybe_mkwrite().

  A shadow stack vma is writable but has different vma
flags, and handled accordingly in maybe_mkwrite().

Signed-off-by: Yu-cheng Yu <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
---
 mm/memory.c   | 5 ++---
 mm/migrate.c  | 3 +--
 mm/mprotect.c | 2 +-
 3 files changed, 4 insertions(+), 6 deletions(-)

Comments

Kirill A. Shutemov April 9, 2021, 3:20 p.m. UTC | #1

On Thu, Apr 01, 2021 at 03:10:50PM -0700, Yu-cheng Yu wrote:
> When serving a page fault, maybe_mkwrite() makes a PTE writable if it is in
> a writable vma.  A shadow stack vma is writable, but its PTEs need
> _PAGE_DIRTY to be set to become writable.  For this reason, maybe_mkwrite()
> has been updated.
> 
> There are a few places that call pte_mkwrite() directly, but have the
> same result as from maybe_mkwrite().  These sites need to be updated for
> shadow stack as well.  Thus, change them to maybe_mkwrite():
> 
> - do_anonymous_page() and migrate_vma_insert_page() check VM_WRITE directly
>   and call pte_mkwrite(), which is the same as maybe_mkwrite().  Change
>   them to maybe_mkwrite().
> 
> - In do_numa_page(), if the numa entry was writable, then pte_mkwrite()
>   is called directly.  Fix it by doing maybe_mkwrite().
> 
> - In change_pte_range(), pte_mkwrite() is called directly.  Replace it with
>   maybe_mkwrite().
> 
>   A shadow stack vma is writable but has different vma
> flags, and handled accordingly in maybe_mkwrite().
> 

Have you checked THP side? Looks like at least do_huge_pmd_numa_page()
needs adjustment, no?

Patch

diff --git a/mm/memory.c b/mm/memory.c
index 5efa07fb6cdc..c70c3847f79d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3561,8 +3561,7 @@  static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 	__SetPageUptodate(page);
 
 	entry = mk_pte(page, vma->vm_page_prot);
-	if (vma->vm_flags & VM_WRITE)
-		entry = pte_mkwrite(pte_mkdirty(entry));
+	entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 
 	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
 			&vmf->ptl);
@@ -4125,7 +4124,7 @@  static vm_fault_t do_numa_page(struct vm_fault *vmf)
 	pte = pte_modify(old_pte, vma->vm_page_prot);
 	pte = pte_mkyoung(pte);
 	if (was_writable)
-		pte = pte_mkwrite(pte);
+		pte = maybe_mkwrite(pte, vma);
 	ptep_modify_prot_commit(vma, vmf->address, vmf->pte, old_pte, pte);
 	update_mmu_cache(vma, vmf->address, vmf->pte);
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 62b81d5257aa..7251c88a3d64 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2976,8 +2976,7 @@  static void migrate_vma_insert_page(struct migrate_vma *migrate,
 		}
 	} else {
 		entry = mk_pte(page, vma->vm_page_prot);
-		if (vma->vm_flags & VM_WRITE)
-			entry = pte_mkwrite(pte_mkdirty(entry));
+		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 	}
 
 	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 94188df1ee55..c1ce78d688b6 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -135,7 +135,7 @@  static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 			if (dirty_accountable && pte_dirty(ptent) &&
 					(pte_soft_dirty(ptent) ||
 					 !(vma->vm_flags & VM_SOFTDIRTY))) {
-				ptent = pte_mkwrite(ptent);
+				ptent = maybe_mkwrite(ptent, vma);
 			}
 			ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent);
 			pages++;