[PATCH v26 20/30] mm/mprotect: Exclude shadow stack from preserve_write

Yu-cheng Yu
2021-04-27T20:45:38Z

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.yu@intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
v25:
- Move is_shadow_stack_mapping() to a separate line.

v24:
- Change arch_shadow_stack_mapping() to is_shadow_stack_mapping().

mm/huge_memory.c | 7 +++++++
mm/mprotect.c | 7 +++++++
2 files changed, 14 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index cf10c3822853..3b841d7efd13 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1824,6 +1824,13 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
return 0;

preserve_write = prot_numa && pmd_write(*pmd);
+
+ /*
+ * Preserve only normal writable huge PMD, but not shadow
+ * stack (RW=0, Dirty=1).
+ */
+ if (is_shadow_stack_mapping(vma->vm_flags))
+ preserve_write = false;
ret = 1;

#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
diff --git a/mm/mprotect.c b/mm/mprotect.c
index c1ce78d688b6..3b2f0d75519f 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -77,6 +77,13 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
pte_t ptent;
bool preserve_write = prot_numa && pte_write(oldpte);

+ /*
+ * Preserve only normal writable PTE, but not shadow
+ * stack (RW=0, Dirty=1).
+ */
+ if (is_shadow_stack_mapping(vma->vm_flags))
+ preserve_write = false;
+
/*
* Avoid trapping faults against the zero or KSM
* pages. See similar comment in change_huge_pmd.
--
2.21.0