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[24.9.64.241]) by smtp.gmail.com with ESMTPSA id p4sm671399ooa.35.2021.07.29.14.33.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Jul 2021 14:33:11 -0700 (PDT) Subject: Re: [PATCH v2] selftests/sgx: Fix Q1 and Q2 calculation in sigstruct.c To: Jarkko Sakkinen Cc: Shuah Khan , 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> <20210727031227.tx2gqx2qg3mg4522@kernel.org> From: Shuah Khan Message-ID: Date: Thu, 29 Jul 2021 15:33:10 -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: <20210727031227.tx2gqx2qg3mg4522@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 7/26/21 9:12 PM, Jarkko Sakkinen wrote: > On Fri, Jul 23, 2021 at 01:53:06PM -0600, Shuah Khan wrote: >> 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? > > Sorry for latency, just came from two week leave. > > glibc does provide bswap for 16, 32, 64 bit numbers but nothing better. > > I have no idea if libssl has such function. Since the test code already > uses this function, and it works, and it's not a newly added function in > this patch, I would consider keeping it. > I will queue this up since it is fixing an important problem. Let's look into if this can be replaced with a lib call when you do cleanups perhaps for the next release. thanks, -- Shuah