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Commit 7798330a authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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: default avatarIan Campbell <ijc@hellion.org.uk>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 297c5eee

mm/mlock.c

+16 −5
Original line number Diff line number Diff line
@@ -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
@@ -168,12 +181,10 @@ 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;

	if (stack_guard_page(vma, start)) {

		addr += PAGE_SIZE;

		nr_pages--;

	}

	}



	while (nr_pages > 0) {

		int i;