[PATCH] prevent NULL mmap in topdown model (49a43876) · Commits · 戴 / test

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>

mm/mmap.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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,

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