Date: Fri, 9 Dec 2016 21:55:31 -0800 From: Eric Biggers <ebiggers3@...il.com> To: Andy Lutomirski <luto@...capital.net> Cc: linux-crypto@...r.kernel.org, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Herbert Xu <herbert@...dor.apana.org.au>, Andrew Lutomirski <luto@...nel.org>, Stephan Mueller <smueller@...onox.de> Subject: Re: Remaining crypto API regressions with CONFIG_VMAP_STACK On Fri, Dec 09, 2016 at 09:25:38PM -0800, Andy Lutomirski wrote: > > The following crypto drivers initialize a scatterlist to point into an > > ahash_request, which may have been allocated on the stack with > > AHASH_REQUEST_ON_STACK(): > > > > drivers/crypto/bfin_crc.c:351 > > drivers/crypto/qce/sha.c:299 > > drivers/crypto/sahara.c:973,988 > > drivers/crypto/talitos.c:1910 > > This are impossible or highly unlikely on x86. > > > drivers/crypto/ccp/ccp-crypto-aes-cmac.c:105,119,142 > > drivers/crypto/ccp/ccp-crypto-sha.c:95,109,124 > > These > > > drivers/crypto/qce/sha.c:325 > > This is impossible on x86. > Thanks for looking into these. I didn't investigate who/what is likely to be using each driver. Of course I would not be surprised to see people want to start supporting virtually mapped stacks on other architectures too. > > > > The "good" news with these bugs is that on x86_64 without CONFIG_DEBUG_SG=y or > > CONFIG_DEBUG_VIRTUAL=y, you can still do virt_to_page() and then page_address() > > on a vmalloc address and get back the same address, even though you aren't > > *supposed* to be able to do this. This will make things still work for most > > people. The bad news is that if you happen to have consumed just about 1 page > > (or N pages) of your stack at the time you call the crypto API, your stack > > buffer may actually span physically non-contiguous pages, so the crypto > > algorithm will scribble over some unrelated page. > > Are you sure? If it round-trips to the same virtual address, it > doesn't matter if the buffer is contiguous. You may be right, I didn't test this. The hash_walk and blkcipher_walk code do go page by page, but I suppose on x86_64 it would just step from one bogus "struct page" to the adjacent one and still map it to the original virtual address. Eric
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