Thread (50 messages) 50 messages, 4 authors, 2021-04-10
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[PATCH v24 20/30] mm/mprotect: Exclude shadow stack from preserve_write

From: Yu-cheng Yu <hidden>
Date: 2021-04-01 22:12:42
Also in: linux-arch, linux-doc, linux-mm, lkml
Subsystem: memory management, memory management - thp (transparent huge page), memory mapping, the rest · Maintainers: Andrew Morton, David Hildenbrand, Lorenzo Stoakes, Liam R. Howlett, Linus Torvalds

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>
Cc: Kirill A. Shutemov <redacted>
---
v24:
- Change arch_shadow_stack_mapping() to is_shadow_stack_mapping().

 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 65fc0aedd577..1d41138c4f74 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1812,12 +1812,17 @@ 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 = is_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..550448dc5ff1 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 = is_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
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