[PATCH 6/9] x86/mm: Introduce ptep_set_wrprotect_flush and related functions

Yu-cheng Yu
2018-06-07T14:40:47Z

The function ptep_set_wrprotect()/huge_ptep_set_wrprotect() is
used by copy_page_range()/copy_hugetlb_page_range() to copy
PTEs.

On x86, when the shadow stack is enabled, only a shadow stack
PTE has the read-only and _PAGE_DIRTY_HW combination. Upon
making a dirty PTE read-only, we move its _PAGE_DIRTY_HW to
_PAGE_DIRTY_SW.

When ptep_set_wrprotect() moves _PAGE_DIRTY_HW to _PAGE_DIRTY_SW,
if the PTE is writable and the mm is shared, another task could
race to set _PAGE_DIRTY_HW again.

Introduce ptep_set_wrprotect_flush(), pmdp_set_wrprotect_flush(),
and huge_ptep_set_wrprotect_flush() to make sure this does not
happen.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
arch/x86/include/asm/pgtable.h | 56 +++++++++++++++++++++++++++++++++++-------
include/asm-generic/pgtable.h | 26 ++++++++++++++++++++
2 files changed, 73 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 0996f8a6979a..1053b940b35c 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -1148,11 +1148,27 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
return pte;
}

-#define __HAVE_ARCH_PTEP_SET_WRPROTECT
-static inline void ptep_set_wrprotect(struct mm_struct *mm,
- unsigned long addr, pte_t *ptep)
-{
- clear_bit(_PAGE_BIT_RW, (unsigned long *)&ptep->pte);
+#define __HAVE_ARCH_PTEP_SET_WRPROTECT_FLUSH
+extern pte_t ptep_clear_flush(struct vm_area_struct *vma,
+ unsigned long address,
+ pte_t *ptep);
+static inline void ptep_set_wrprotect_flush(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *ptep)
+{
+ bool rw;
+
+ rw = test_and_clear_bit(_PAGE_BIT_RW, (unsigned long *)&ptep->pte);
+ if (IS_ENABLED(CONFIG_X86_INTEL_SHADOW_STACK_USER)) {
+ struct mm_struct *mm = vma->vm_mm;
+ pte_t pte;
+
+ if (rw && (atomic_read(&mm->mm_users) > 1))
+ pte = ptep_clear_flush(vma, addr, ptep);
+ else
+ pte = *ptep;
+ pte = pte_move_flags(pte, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW);
+ set_pte_at(mm, addr, ptep, pte);
+ }
}

#define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
@@ -1198,11 +1214,33 @@ static inline pud_t pudp_huge_get_and_clear(struct mm_struct *mm,
return native_pudp_get_and_clear(pudp);
}

-#define __HAVE_ARCH_PMDP_SET_WRPROTECT
-static inline void pmdp_set_wrprotect(struct mm_struct *mm,
- unsigned long addr, pmd_t *pmdp)
+#define __HAVE_ARCH_HUGE_PTEP_SET_WRPROTECT_FLUSH
+static inline void huge_ptep_set_wrprotect_flush(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *ptep)
{
- clear_bit(_PAGE_BIT_RW, (unsigned long *)pmdp);
+ ptep_set_wrprotect_flush(vma, addr, ptep);
+}
+
+#define __HAVE_ARCH_PMDP_SET_WRPROTECT_FLUSH
+extern pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma,
+ unsigned long address,
+ pmd_t *pmdp);
+static inline void pmdp_set_wrprotect_flush(struct vm_area_struct *vma,
+ unsigned long addr, pmd_t *pmdp)
+{ bool rw;
+
+ rw = test_and_clear_bit(_PAGE_BIT_RW, (unsigned long *)&pmdp);
+ if (IS_ENABLED(CONFIG_X86_INTEL_SHADOW_STACK_USER)) {
+ struct mm_struct *mm = vma->vm_mm;
+ pmd_t pmd;
+
+ if (rw && (atomic_read(&mm->mm_users) > 1))
+ pmd = pmdp_huge_clear_flush(vma, addr, pmdp);
+ else
+ pmd = *pmdp;
+ pmd = pmd_move_flags(pmd, _PAGE_DIRTY_HW, _PAGE_DIRTY_SW);
+ set_pmd_at(mm, addr, pmdp, pmd);
+ }
}

#define pud_write pud_write
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 3f6f998509f0..9bcfdfc045bb 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -121,6 +121,15 @@ static inline int pmdp_clear_flush_young(struct vm_area_struct *vma,
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#endif

+#ifndef __HAVE_ARCH_HUGE_PTEP_SET_WRPROTECT_FLUSH
+static inline void huge_ptep_set_wrorptect_flush(struct vm_area_struct *vma,
+ unsigned long addr,
+ pte_t *ptep)
+{
+ huge_ptep_set_wrprotect(vma->vm_mm, addr, ptep);
+}
+#endif
+
#ifndef __HAVE_ARCH_PTEP_GET_AND_CLEAR
static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
unsigned long address,
@@ -226,6 +235,15 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
}
#endif

+#ifndef __HAVE_ARCH_PTEP_SET_WRPROTECT_FLUSH
+static inline void ptep_set_wrprotect_flush(struct vm_area_struct *vma,
+ unsigned long address,
+ pte_t *ptep)
+{
+ ptep_set_wrprotect(vma->vm_mm, address, ptep);
+}
+#endif
+
#ifndef pte_savedwrite
#define pte_savedwrite pte_write
#endif
@@ -266,6 +284,14 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#endif
+#ifndef __HAVE_ARCH_PMDP_SET_WRPROTECT_FLUSH
+static inline void pmdp_set_wrprotect_flush(struct vm_area_struct *vma,
+ unsigned long address,
+ pmd_t *pmdp)
+{
+ pmdp_set_wrprotect(vma->vm_mm, address, pmdp);
+}
+#endif
#ifndef __HAVE_ARCH_PUDP_SET_WRPROTECT
#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
static inline void pudp_set_wrprotect(struct mm_struct *mm,
--
2.15.1