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Commit 0e8e50e2 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

mm: make stack guard page logic use vm_prev pointer 



Like the mlock() change previously, this makes the stack guard check
code use vma->vm_prev to see what the mapping below the current stack
is, rather than have to look it up with find_vma().

Also, accept an abutting stack segment, since that happens naturally if
you split the stack with mlock or mprotect.

Tested-by: default avatarIan Campbell <ijc@hellion.org.uk>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7798330a

mm/memory.c

+11 −4
Original line number Diff line number Diff line
@@ -2770,11 +2770,18 @@ static inline int check_stack_guard_page(struct vm_area_struct *vma, unsigned lo 
{

	address &= PAGE_MASK;

	if ((vma->vm_flags & VM_GROWSDOWN) && address == vma->vm_start) {

		address -= PAGE_SIZE;

		if (find_vma(vma->vm_mm, address) != vma)

			return -ENOMEM;

		struct vm_area_struct *prev = vma->vm_prev;



		/*

		 * Is there a mapping abutting this one below?

		 *

		 * That's only ok if it's the same stack mapping

		 * that has gotten split..

		 */

		if (prev && prev->vm_end == address)

			return prev->vm_flags & VM_GROWSDOWN ? 0 : -ENOMEM;



		expand_stack(vma, address);

		expand_stack(vma, address - PAGE_SIZE);

	}

	return 0;

}