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Subject[RFC PATCH v2 16/27] mm: Modify can_follow_write_pte/pmd for shadow stack
Date
There are three possible shadow stack PTE settings:

Normal SHSTK PTE: (R/O + DIRTY_HW)
SHSTK PTE COW'ed: (R/O + DIRTY_HW)
SHSTK PTE shared as R/O data: (R/O + DIRTY_SW)

Update can_follow_write_pte/pmd for the shadow stack.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
---
mm/gup.c | 11 ++++++++---
mm/huge_memory.c | 10 +++++++---
2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index b70d7ba7cc13..00171ee847af 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -64,10 +64,13 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
* FOLL_FORCE can write to even unwritable pte's, but only
* after we've gone through a COW cycle and they are dirty.
*/
-static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
+static inline bool can_follow_write_pte(pte_t pte, unsigned int flags,
+ bool shstk)
{
+ bool pte_cowed = shstk ? is_shstk_pte(pte):pte_dirty(pte);
+
return pte_write(pte) ||
- ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
+ ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_cowed);
}

static struct page *follow_page_pte(struct vm_area_struct *vma,
@@ -78,7 +81,9 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
struct page *page;
spinlock_t *ptl;
pte_t *ptep, pte;
+ bool shstk;

+ shstk = is_shstk_mapping(vma->vm_flags);
retry:
if (unlikely(pmd_bad(*pmd)))
return no_page_table(vma, flags);
@@ -105,7 +110,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
}
if ((flags & FOLL_NUMA) && pte_protnone(pte))
goto no_page;
- if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
+ if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags, shstk)) {
pte_unmap_unlock(ptep, ptl);
return NULL;
}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7f3e11d3b64a..db4c689a960a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1389,10 +1389,13 @@ int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
* FOLL_FORCE can write to even unwritable pmd's, but only
* after we've gone through a COW cycle and they are dirty.
*/
-static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags)
+static inline bool can_follow_write_pmd(pmd_t pmd, unsigned int flags,
+ bool shstk)
{
+ bool pmd_cowed = shstk ? is_shstk_pmd(pmd):pmd_dirty(pmd);
+
return pmd_write(pmd) ||
- ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_dirty(pmd));
+ ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pmd_cowed);
}

struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
@@ -1402,10 +1405,11 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
{
struct mm_struct *mm = vma->vm_mm;
struct page *page = NULL;
+ bool shstk = is_shstk_mapping(vma->vm_flags);

assert_spin_locked(pmd_lockptr(mm, pmd));

- if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags))
+ if (flags & FOLL_WRITE && !can_follow_write_pmd(*pmd, flags, shstk))
goto out;

/* Avoid dumping huge zero page */
--
2.17.1
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