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Old 11-24-2011, 09:07 AM
Paolo Pisati
 
Default mm: make the mlock() stack guard page checks stricter

From: Linus Torvalds <torvalds@linux-foundation.org>

commit 7798330ac8114c731cfab83e634c6ecedaa233d7 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
(cherry picked from commit e89cfc48a21fa83088e083fe6341ff803ab32f8e)

BugLink: http://launchpad.net/bugs/893190

Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
---
mm/mlock.c | 21 ++++++++++++++++-----
1 files changed, 16 insertions(+), 5 deletions(-)

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 @@ void munlock_vma_page(struct page *page)
}
}

+/* 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 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
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) {
--
1.7.5.4


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