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SubjectRe: [PATCH] mm: Add additional consistency check
On Fri, 31 Mar 2017 09:40:28 -0700 Kees Cook <keescook@chromium.org> wrote:

> As found in PaX, this adds a cheap check on heap consistency, just to
> notice if things have gotten corrupted in the page lookup.

"As found in PaX" isn't a very illuminating justification for such a
change. Was there a real kernel bug which this would have exposed, or
what?

> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -384,6 +384,7 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
> return s;
>
> page = virt_to_head_page(x);
> + BUG_ON(!PageSlab(page));
> cachep = page->slab_cache;
> if (slab_equal_or_root(cachep, s))
> return cachep;

BUG_ON might be too severe. I expect the kindest VM_WARN_ON_ONCE()
would suffice here, but without more details it is hard to say.

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