vma->vm_page_prot is read lockless from the rmap_walk, it may be
updated concurrently and this prevents the risk of reading
intermediate values.
v2: avoid semantic change noticed by Hillf Danton in
vma_wants_writenotify().
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
include/linux/mm.h | 2 +-
mm/huge_memory.c | 2 +-
mm/migrate.c | 2 +-
mm/mmap.c | 16 +++++++++-------
mm/mprotect.c | 2 +-
5 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2334052..67b48fb 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1529,7 +1529,7 @@ static inline int pte_devmap(pte_t pte)
}
#endif
-int vma_wants_writenotify(struct vm_area_struct *vma);
+int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot);
extern pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
spinlock_t **ptl);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a6abd76..ccdc703 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1566,7 +1566,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
if (soft_dirty)
entry = pte_swp_mksoft_dirty(entry);
} else {
- entry = mk_pte(page + i, vma->vm_page_prot);
+ entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));
entry = maybe_mkwrite(entry, vma);
if (!write)
entry = pte_wrprotect(entry);
diff --git a/mm/migrate.c b/mm/migrate.c
index f7ee04a..99250ae 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -234,7 +234,7 @@ static int remove_migration_pte(struct page *new, struct vm_area_struct *vma,
goto unlock;
get_page(new);
- pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
+ pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot)));
if (pte_swp_soft_dirty(*ptep))
pte = pte_mksoft_dirty(pte);
diff --git a/mm/mmap.c b/mm/mmap.c
index d8b5fb3..12f32dd 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -111,13 +111,15 @@ static pgprot_t vm_pgprot_modify(pgprot_t oldprot, unsigned long vm_flags)
void vma_set_page_prot(struct vm_area_struct *vma)
{
unsigned long vm_flags = vma->vm_flags;
+ pgprot_t vm_page_prot;
- vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
- if (vma_wants_writenotify(vma)) {
+ vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
+ if (vma_wants_writenotify(vma, vm_page_prot)) {
vm_flags &= ~VM_SHARED;
- vma->vm_page_prot = vm_pgprot_modify(vma->vm_page_prot,
- vm_flags);
+ vm_page_prot = vm_pgprot_modify(vm_page_prot, vm_flags);
}
+ /* remove_protection_ptes reads vma->vm_page_prot without mmap_sem */
+ WRITE_ONCE(vma->vm_page_prot, vm_page_prot);
}
/*
@@ -1484,7 +1486,7 @@ SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
* to the private version (using protection_map[] without the
* VM_SHARED bit).
*/
-int vma_wants_writenotify(struct vm_area_struct *vma)
+int vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot)
{
vm_flags_t vm_flags = vma->vm_flags;
const struct vm_operations_struct *vm_ops = vma->vm_ops;
@@ -1499,8 +1501,8 @@ int vma_wants_writenotify(struct vm_area_struct *vma)
/* The open routine did something to the protections that pgprot_modify
* won't preserve? */
- if (pgprot_val(vma->vm_page_prot) !=
- pgprot_val(vm_pgprot_modify(vma->vm_page_prot, vm_flags)))
+ if (pgprot_val(vm_page_prot) !=
+ pgprot_val(vm_pgprot_modify(vm_page_prot, vm_flags)))
return 0;
/* Do we need to track softdirty? */
diff --git a/mm/mprotect.c b/mm/mprotect.c
index e55e2c9..ec91dfd 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -328,7 +328,7 @@ success:
* held in write mode.
*/
vma->vm_flags = newflags;
- dirty_accountable = vma_wants_writenotify(vma);
+ dirty_accountable = vma_wants_writenotify(vma, vma->vm_page_prot);
vma_set_page_prot(vma);
change_protection(vma, start, end, vma->vm_page_prot,
--
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