[PATCH] prevent NULL mmap in topdown model

Prevent the topdown allocator from allocating mmap areas all the way
down to address zero.

We still allow a MAP_FIXED mapping of page 0 (needed for various things,
ranging from Wine and DOSEMU to people who want to allow speculative
loads off a NULL pointer).

Tested by Chris Wright.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index 01f9793..63df2d6 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1244,7 +1244,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
        addr = mm->free_area_cache;
 
        /* make sure it can fit in the remaining address space */
-       if (addr >= len) {
+       if (addr > len) {
                vma = find_vma(mm, addr-len);
                if (!vma || addr <= vma->vm_start)
                        /* remember the address as a hint for next time */
@@ -1266,7 +1266,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 
                /* try just below the current vma->vm_start */
                addr = vma->vm_start-len;
-       } while (len <= vma->vm_start);
+       } while (len < vma->vm_start);
 
        /*
         * A failed mmap() very likely causes application failure,