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

[Jia Zhang]

On 2021/3/2 下午9:47, Jarkko Sakkinen wrote:
> On Mon, Mar 01, 2021 at 09:54:37PM -0800, Andy Lutomirski wrote:
>> On Mon, Mar 1, 2021 at 9:06 PM Tianjia Zhang
>> <tianjia.zhang@xxxxxxxxxxxxxxxxx> wrote:
>>>
>>>
>>>
>>> On 3/1/21 5:54 PM, Jarkko Sakkinen wrote:
>>>> 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
>>>>
>>>
>>> When use openssl to generate a key instead of using the built-in
>>> sign_key.pem, there is a probability that will encounter this problem.
>>>
>>> Here is a problematic key I encountered. The calculated q1 and q2 of
>>> this key are both 383 bytes, If the length is not processed, the
>>> hardware signature will fail.
>>
>> Presumably the issue is that some keys have parameters that have
>> enough leading 0 bits to be effectively shorter.  The openssl API
>> (and, sadly, a bunch  of the ASN.1 stuff) treats these parameters as
>> variable-size integers.
> 
> But the test uses a static key. It used to generate a key on fly but

IMO even though the test code, it comes from the linux kernel, meaning
that its quality has a certain guarantee and it is a good reference, so
the test code still needs to ensure its correctness.

Jia

> in some of the last versions I replaced key generation with a static
> key:
> 
> static RSA *gen_sign_key(void)
> {
> 	unsigned long sign_key_length;
> 	BIO *bio;
> 	RSA *key;
> 
> 	sign_key_length = (unsigned long)&sign_key_end -
> 			  (unsigned long)&sign_key;
> 
> 	bio = BIO_new_mem_buf(&sign_key, sign_key_length);
> 	if (!bio)
> 		return NULL;
> 
> 	key = PEM_read_bio_RSAPrivateKey(bio, NULL, NULL, NULL);
> 	BIO_free(bio);
> 
> 	return key;
> }
> 
> /Jarkko
>