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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Mon, 18 Mar 2019 10:13:39 +0100
Message-ID: <CAKv+Gu_w_d5AbkYu=fdK1ver97G4O_rqu9o9tNy_-zNaAOnkkA@mail.gmail.com>
Subject: Re: [PATCH] crypto: vmx - fix copy-paste error in CTR mode
To:     Michael Ellerman <mpe@ellerman.id.au>
Cc:     Eric Biggers <ebiggers@kernel.org>, Daniel Axtens <dja@axtens.net>,
        leo.barbosa@canonical.com,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Stephan Mueller <smueller@chronox.de>, nayna@linux.ibm.com,
        omosnacek@gmail.com, leitao@debian.org, pfsmorigo@gmail.com,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>, marcelo.cerri@canonical.com,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
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Sender: linux-crypto-owner@vger.kernel.org
Precedence: bulk

On Mon, 18 Mar 2019 at 09:41, Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> Eric Biggers <ebiggers@kernel.org> writes:
> > On Fri, Mar 15, 2019 at 03:24:35PM +1100, Daniel Axtens wrote:
> ...
> >> >> This leads to corruption of the IV, which leads to subsequent blocks
> >> >> being corrupted.
> >> >>
> >> >> This can be detected with libkcapi test suite, which is available at
> >> >> https://github.com/smuellerDD/libkcapi
> >> >
> >> > Is this also detected by the kernel's crypto self-tests, and if not why not?
> >> > What about with the new option CONFIG_CRYPTO_MANAGER_EXTRA_TESTS=y?
> >>
> >> It seems the self-tests do not catch it. To catch it, there has to be a
> >> test where the blkcipher_walk creates a walk.nbytes such that
> >> [(the number of AES blocks) mod 8] is either 2 or 3. This happens with
> >> AF_ALG pretty frequently, but when I booted with self-tests it only hit
> >> 1, 4, 5, 6 and 7 - it missed 0, 2 and 3.
> >>
> >> I don't have the EXTRA_TESTS option - I'm testing with 5.0-rc6. Is it in
> >> -next?
> >
> > The improvements I recently made to the self-tests are intended to catch exactly
> > this sort of bug.  They were just merged for v5.1, so try the latest mainline.
> > This almost certainly would be caught by EXTRA_TESTS (and if not I'd want to
> > know), but it may be caught by the regular self-tests now too.
>
> Enabling the crypto tests (CONFIG_CRYPTO_MANAGER_DISABLE_TESTS=n)
> actually hides the bug for me.
>
> By which I mean I can't trigger the bug via kcapi-enc-tests.sh, because
> the VMX code is never called.
>
> ie:
>   # zgrep -e CRYPTO_MANAGER -e VMX /proc/config.gz
>   CONFIG_CRYPTO_MANAGER=y
>   CONFIG_CRYPTO_MANAGER2=y
>   # CONFIG_CRYPTO_MANAGER_DISABLE_TESTS is not set
>   # CONFIG_CRYPTO_MANAGER_EXTRA_TESTS is not set
>   CONFIG_CRYPTO_DEV_VMX=y
>   CONFIG_CRYPTO_DEV_VMX_ENCRYPT=y
>
>   # echo "p:p8_aes_ctr_crypt p8_aes_ctr_crypt" > /sys/kernel/debug/tracing/kprobe_events
>   # echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
>   # ./kcapi-enc-test.sh
>   ...
>   Number of failures: 0
>   # grep -c p8_aes_ctr_crypt  /sys/kernel/debug/tracing/trace
>   0
>
>
> I don't understand how the crypto core chooses which crypto_alg to use,
> but I didn't expect enabling the tests to change it?
>

This is not entirely unexpected. Based on the tests, algos that are
found to be broken are disregarded for further use, and you should see
a warning in the kernel log about this.