Thread (30 messages) 30 messages, 2 authors, 2021-10-14

[PATCH v22 20/28] mm/mprotect: Exclude shadow stack from preserve_write

STALE1813d

From: Yu-cheng Yu <hidden>
Date: 2021-03-10 22:02:19
Also in: linux-api, linux-doc, linux-mm, lkml
Subsystem: memory management, memory management - thp (transparent huge page), memory mapping, the rest · Maintainers: Andrew Morton, David Hildenbrand, Liam R. Howlett, Lorenzo Stoakes, Linus Torvalds

Revision v22 of 25 in this series.

Revisions (25)
  1. v6 [diff vs current]
  2. v7 [diff vs current]
  3. v8 [diff vs current]
  4. v9 [diff vs current]
  5. v10 [diff vs current]
  6. v11 [diff vs current]
  7. v12 [diff vs current]
  8. v13 [diff vs current]
  9. v14 [diff vs current]
  10. v15 [diff vs current]
  11. v16 [diff vs current]
  12. v17 [diff vs current]
  13. v18 [diff vs current]
  14. v19 [diff vs current]
  15. v20 [diff vs current]
  16. v21 [diff vs current]
  17. v22 current
  18. v23 [diff vs current]
  19. v24 [diff vs current]
  20. v25 [diff vs current]
  21. v26 [diff vs current]
  22. v27 [diff vs current]
  23. v28 [diff vs current]
  24. v29 [diff vs current]
  25. v30 [diff vs current] 
In change_pte_range(), when a PTE is changed for prot_numa, _PAGE_RW is
preserved to avoid the additional write fault after the NUMA hinting fault.
However, pte_write() now includes both normal writable and shadow stack
(RW=0, Dirty=1) PTEs, but the latter does not have _PAGE_RW and has no need
to preserve it.

Exclude shadow stack from preserve_write test, and apply the same change to
change_huge_pmd().

Signed-off-by: Yu-cheng Yu <redacted>
---
 mm/huge_memory.c | 7 ++++++-
 mm/mprotect.c    | 9 ++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index de8c8b94e840..6b7dc5dd94de 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1816,12 +1816,17 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 	bool prot_numa = cp_flags & MM_CP_PROT_NUMA;
 	bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
 	bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
+	bool shstk = arch_shadow_stack_mapping(vma->vm_flags);
 
 	ptl = __pmd_trans_huge_lock(pmd, vma);
 	if (!ptl)
 		return 0;
 
-	preserve_write = prot_numa && pmd_write(*pmd);
+	/*
+	 * Preserve only normal writable huge PMD, but not shadow
+	 * stack (RW=0, Dirty=1).
+	 */
+	preserve_write = prot_numa && pmd_write(*pmd) && !shstk;
 	ret = 1;
 
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
diff --git a/mm/mprotect.c b/mm/mprotect.c
index c1ce78d688b6..e69278b346a9 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -75,7 +75,14 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 		oldpte = *pte;
 		if (pte_present(oldpte)) {
 			pte_t ptent;
-			bool preserve_write = prot_numa && pte_write(oldpte);
+			bool shstk = arch_shadow_stack_mapping(vma->vm_flags);
+			bool preserve_write;
+
+			/*
+			 * Preserve only normal writable PTE, but not shadow
+			 * stack (RW=0, Dirty=1).
+			 */
+			preserve_write = prot_numa && pte_write(oldpte) && !shstk;
 
 			/*
 			 * Avoid trapping faults against the zero or KSM
-- 
2.21.0
Other recent patches touching these files
Keyboard shortcuts
hback out one level
jnext message in thread
kprevious message in thread
ldrill in
Escclose help / fold thread tree
?toggle this help