[PATCH] Don't allow the stack to grow into hugetlb reserved regions

When expanding the stack, we don't currently check if the VMA will cross
into an area of the address space that is reserved for hugetlb pages.
Subsequent faults on the expanded portion of such a VMA will confuse the
low-level MMU code, resulting in an OOPS. Check for this.

Signed-off-by: Adam Litke <[e-mail]>
Cc: David Gibson <[e-mail]>
Cc: William Lee Irwin III <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/mmap.c

···
 {
 	struct mm_struct *mm = vma->vm_mm;
 	struct rlimit *rlim = current->signal->rlim;
+	unsigned long new_start;
 
 	/* address space limit tests */
 	if (!may_expand_vm(mm, grow))
···
 		if (locked > limit && !capable(CAP_IPC_LOCK))
 			return -ENOMEM;
 	}
+
+	/* Check to ensure the stack will not grow into a hugetlb-only region */
+	new_start = (vma->vm_flags & VM_GROWSUP) ? vma->vm_start :
+			vma->vm_end - size;
+	if (is_hugepage_only_range(vma->vm_mm, new_start, size))
+		return -EFAULT;
 
 	/*
 	 * Overcommit..  This must be the final test, as it will