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[24.9.64.241]) by smtp.gmail.com with ESMTPSA id t1sm16925109ilf.34.2021.07.23.12.53.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 23 Jul 2021 12:53:07 -0700 (PDT) Subject: Re: [PATCH v2] selftests/sgx: Fix Q1 and Q2 calculation in sigstruct.c To: Jarkko Sakkinen , Shuah Khan Cc: linux-kselftest@vger.kernel.org, linux-sgx@vger.kernel.org, Reinette Chatre , Borislav Petkov , Tianjia Zhang , Dave Hansen , linux-kernel@vger.kernel.org, Shuah Khan References: <20210705050922.63710-1-jarkko@kernel.org> From: Shuah Khan Message-ID: Date: Fri, 23 Jul 2021 13:53:06 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210705050922.63710-1-jarkko@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On 7/4/21 11:09 PM, Jarkko Sakkinen wrote: > From: Tianjia Zhang > > Q1 and Q2 are numbers with *maximum* length of 384 bytes. If the calculated > length of Q1 and Q2 is less than 384 bytes, things will go wrong. > > E.g. if Q2 is 383 bytes, then > > 1. The bytes of q2 are copied to sigstruct->q2 in calc_q1q2(). > 2. The entire sigstruct->q2 is reversed, which results it being > 256 * Q2, given that the last byte of sigstruct->q2 is added > to before the bytes given by calc_q1q2(). > > Either change in key or measurement can trigger the bug. E.g. an unmeasured > heap could cause a devastating change in Q1 or Q2. > > Reverse exactly the bytes of Q1 and Q2 in calc_q1q2() before returning to > the caller. > > Fixes: dedde2634570 ("selftests/sgx: Trigger the reclaimer in the selftests") > Link: https://lore.kernel.org/linux-sgx/20210301051836.30738-1-tianjia.zhang@linux.alibaba.com/ > Signed-off-by: Tianjia Zhang > Signed-off-by: Jarkko Sakkinen > --- > The original patch did a bad job explaining the code change but it > turned out making sense. I wrote a new description. > > v2: > - Added a fixes tag. > tools/testing/selftests/sgx/sigstruct.c | 41 +++++++++++++------------ > 1 file changed, 21 insertions(+), 20 deletions(-) > > diff --git a/tools/testing/selftests/sgx/sigstruct.c b/tools/testing/selftests/sgx/sigstruct.c > index dee7a3d6c5a5..92bbc5a15c39 100644 > --- a/tools/testing/selftests/sgx/sigstruct.c > +++ b/tools/testing/selftests/sgx/sigstruct.c > @@ -55,10 +55,27 @@ static bool alloc_q1q2_ctx(const uint8_t *s, const uint8_t *m, > return true; > } > > +static void reverse_bytes(void *data, int length) > +{ > + int i = 0; > + int j = length - 1; > + uint8_t temp; > + uint8_t *ptr = data; > + > + while (i < j) { > + temp = ptr[i]; > + ptr[i] = ptr[j]; > + ptr[j] = temp; > + i++; > + j--; > + } > +} I was just about apply this one and noticed this reverse_bytes(). Aren't there byteswap functions you could call instead of writing your own? thanks, -- Shuah