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SubjectRe: [PATCH v2] selftests/sgx: Fix Q1 and Q2 calculation in sigstruct.c
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On 7/4/21 11:09 PM, Jarkko Sakkinen wrote:
> From: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
>
> 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 <tianjia.zhang@linux.alibaba.com>
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
> 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

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