From patchwork Thu Nov 24 10:07:22 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [2/6] mm: make the mlock() stack guard page checks stricter From: Paolo Pisati X-Patchwork-Id: 127465 Message-Id: <1322129246-5397-3-git-send-email-paolo.pisati@canonical.com> To: kernel-team@lists.ubuntu.com Date: Thu, 24 Nov 2011 11:07:22 +0100 From: Linus Torvalds 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 Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman (cherry picked from commit e89cfc48a21fa83088e083fe6341ff803ab32f8e) BugLink: http://launchpad.net/bugs/893190 Signed-off-by: Paolo Pisati --- 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) {