Re: Remaining crypto API regressions with CONFIG_VMAP_STACK

From	Eric Biggers <ebiggers3@gmail.com>
Newsgroups	linux.kernel
Subject	Re: Remaining crypto API regressions with CONFIG_VMAP_STACK
Date	2016-12-10 07:00 +0100
Message-ID	<sMIRr-4Ie-1@gated-at.bofh.it> (permalink)
References	<sMCsG-UG-11@gated-at.bofh.it> <sMIoq-4xC-13@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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

Thread

Remaining crypto API regressions with CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 00:10 +0100
  Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-10 06:30 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-10 06:40 +0100
      Re: [kernel-hardening] Re: Remaining crypto API regressions with  CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 07:10 +0100
        Re: [kernel-hardening] Re: Remaining crypto API regressions with  CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-10 09:20 +0100
          Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 09:40 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-10 06:40 +0100
      Re: [kernel-hardening] Re: Remaining crypto API regressions with  CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 07:40 +0100
      Re: [kernel-hardening] Re: Remaining crypto API regressions with CONFIG_VMAP_STACK "Jason A. Donenfeld" <Jason@zx2c4.com> - 2016-12-10 15:50 +0100
        Re: [kernel-hardening] Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-10 18:50 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-10 07:00 +0100
  Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-11 20:20 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Eric Biggers <ebiggers3@gmail.com> - 2016-12-12 00:40 +0100
  Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-12 19:40 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-13 04:40 +0100
      Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Andy Lutomirski <luto@amacapital.net> - 2016-12-13 18:10 +0100
        Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-14 06:00 +0100
    Re: Remaining crypto API regressions with CONFIG_VMAP_STACK Herbert Xu <herbert@gondor.apana.org.au> - 2016-12-13 04:50 +0100

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