mm: make the mlock() stack guard page checks stricter
If we've split the stack vma, only the lowest one has the guard page.
Now that we have a doubly linked list of vma's, checking this is trivial.
Tested-by: Ian Campbell <ijc@hellion.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/mlock.c b/mm/mlock.c
index 49e5e4c..cbae7c5 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -135,6 +135,19 @@
}
}
+/* Is the vma a continuation of the stack vma above it? */
+static inline int vma_stack_continue(struct vm_area_struct *vma, unsigned long addr)
+{
+ return vma && (vma->vm_end == addr) && (vma->vm_flags & VM_GROWSDOWN);
+}
+
+static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr)
+{
+ return (vma->vm_flags & VM_GROWSDOWN) &&
+ (vma->vm_start == addr) &&
+ !vma_stack_continue(vma->vm_prev, addr);
+}
+
/**
* __mlock_vma_pages_range() - mlock a range of pages in the vma.
* @vma: target vma
@@ -168,11 +181,9 @@
gup_flags |= FOLL_WRITE;
/* We don't try to access the guard page of a stack vma */
- if (vma->vm_flags & VM_GROWSDOWN) {
- if (start == vma->vm_start) {
- start += PAGE_SIZE;
- nr_pages--;
- }
+ if (stack_guard_page(vma, start)) {
+ addr += PAGE_SIZE;
+ nr_pages--;
}
while (nr_pages > 0) {
