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

[Yu-cheng Yu]

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 <yu-cheng...@intel.com>
---
 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