Re: [PATCH] selftests/sgx: fix EINIT failure dueto SGX_INVALID_SIGNATURE

From: Jarkko Sakkinen <jarkko@kernel.org>
To: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Sean Christopherson <seanjc@google.com>,
	Shuah Khan <shuah@kernel.org>,
	x86@kernel.org, linux-sgx@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
	Jia Zhang <zhang.jia@linux.alibaba.com>
Subject: Re: [PATCH] selftests/sgx: fix EINIT failure dueto SGX_INVALID_SIGNATURE
Date: Mon, 1 Mar 2021 11:54:29 +0200	[thread overview]
Message-ID: <YDy51R2Wva7s+k/x@kernel.org> (raw)
In-Reply-To: <20210301051836.30738-1-tianjia.zhang@linux.alibaba.com>

On Mon, Mar 01, 2021 at 01:18:36PM +0800, Tianjia Zhang wrote:
> q2 is not always 384-byte length. Sometimes it only has 383-byte.

What does determine this?

> In this case, the valid portion of q2 is reordered reversely for
> little endian order, and the remaining portion is filled with zero.

I'm presuming that you want to say "In this case, q2 needs to be reversed because...".

I'm lacking these details:

1. Why the length of Q2 can vary?
2. Why reversing the bytes is the correct measure to counter-measure
   this variation?

/Jarkko

> Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
> ---
>  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--;
> +	}
> +}
> +
>  static bool calc_q1q2(const uint8_t *s, const uint8_t *m, uint8_t *q1,
>  		      uint8_t *q2)
>  {
>  	struct q1q2_ctx ctx;
> +	int len;
>  
>  	if (!alloc_q1q2_ctx(s, m, &ctx)) {
>  		fprintf(stderr, "Not enough memory for Q1Q2 calculation\n");
> @@ -89,8 +106,10 @@ static bool calc_q1q2(const uint8_t *s, const uint8_t *m, uint8_t *q1,
>  		goto out;
>  	}
>  
> -	BN_bn2bin(ctx.q1, q1);
> -	BN_bn2bin(ctx.q2, q2);
> +	len = BN_bn2bin(ctx.q1, q1);
> +	reverse_bytes(q1, len);
> +	len = BN_bn2bin(ctx.q2, q2);
> +	reverse_bytes(q2, len);
>  
>  	free_q1q2_ctx(&ctx);
>  	return true;
> @@ -152,22 +171,6 @@ static RSA *gen_sign_key(void)
>  	return key;
>  }
>  
> -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--;
> -	}
> -}
> -
>  enum mrtags {
>  	MRECREATE = 0x0045544145524345,
>  	MREADD = 0x0000000044444145,
> @@ -367,8 +370,6 @@ bool encl_measure(struct encl *encl)
>  	/* BE -> LE */
>  	reverse_bytes(sigstruct->signature, SGX_MODULUS_SIZE);
>  	reverse_bytes(sigstruct->modulus, SGX_MODULUS_SIZE);
> -	reverse_bytes(sigstruct->q1, SGX_MODULUS_SIZE);
> -	reverse_bytes(sigstruct->q2, SGX_MODULUS_SIZE);
>  
>  	EVP_MD_CTX_destroy(ctx);
>  	RSA_free(key);
> -- 
> 2.19.1.3.ge56e4f7
> 
> 