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Date: Mon, 31 Oct 2022 08:22:50 -0700 From: Kees Cook <keescook@...omium.org> To: Matthew Wilcox <willy@...radead.org> Cc: Vlastimil Babka <vbabka@...e.cz>, Anders Roxell <anders.roxell@...aro.org>, kernel test robot <oliver.sang@...el.com>, Andrew Morton <akpm@...ux-foundation.org>, David Rientjes <rientjes@...gle.com>, Marco Elver <elver@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, linux-mm@...ck.org, Andrey Konovalov <andreyknvl@...il.com>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH v4] mempool: Do not use ksize() for poisoning On Mon, Oct 31, 2022 at 03:12:33PM +0000, Matthew Wilcox wrote: > On Mon, Oct 31, 2022 at 04:00:25PM +0100, Vlastimil Babka wrote: > > +++ b/mm/mempool.c > > @@ -57,8 +57,10 @@ static void __check_element(mempool_t *pool, void *element, size_t size) > > static void check_element(mempool_t *pool, void *element) > > { > > /* Mempools backed by slab allocator */ > > - if (pool->free == mempool_free_slab || pool->free == mempool_kfree) { > > + if (pool->free == mempool_kfree) { > > __check_element(pool, element, (size_t)pool->pool_data); > > + } else if (pool->free == mempool_free_slab) { > > + __check_element(pool, element, kmem_cache_size(pool->pool_data)); > > } else if (pool->free == mempool_free_pages) { > > /* Mempools backed by page allocator */ > > int order = (int)(long)pool->pool_data; > > I had a quick look at this to be sure I understood what was going on, > and I found a grotesque bug that has been with us since the introduction > of check_element() in 2015. > > + if (pool->free == mempool_free_pages) { > + int order = (int)(long)pool->pool_data; > + void *addr = kmap_atomic((struct page *)element); > + > + __check_element(pool, addr, 1UL << (PAGE_SHIFT + order)); > + kunmap_atomic(addr); > > kmap_atomic() and friends only map a single page. So this is all > nonsense for HIGHMEM kernels, GFP_HIGHMEM allocations and order > 0. > The consequence of doing that will be calling memset(POISON_INUSE) > on random pages that we don't own. Ah-ha! Thank you both! Seems like the first fix should be squashed and the latter one is separate? Or just put it all together? -- Kees Cook
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