linux-kernel - Re: [PATCH v2 2/2] certs: Add support for using elliptic curve keys for signing modules

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Message-ID: <794ef635-de91-9207-f28b-ab6805fd95c9@linux.ibm.com>
Date:   Tue, 20 Apr 2021 17:02:44 -0400
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     keyrings@...r.kernel.org, dhowells@...hat.com, zohar@...ux.ibm.com,
        jarkko@...nel.org, nayna@...ux.ibm.com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] certs: Add support for using elliptic curve keys
 for signing modules


On 4/20/21 10:03 AM, Jessica Yu wrote:
> +++ Stefan Berger [08/04/21 11:24 -0400]:
>>
>> diff --git a/crypto/asymmetric_keys/pkcs7_parser.c 
>> b/crypto/asymmetric_keys/pkcs7_parser.c
>> index 967329e0a07b..2546ec6a0505 100644
>> --- a/crypto/asymmetric_keys/pkcs7_parser.c
>> +++ b/crypto/asymmetric_keys/pkcs7_parser.c
>> @@ -269,6 +269,10 @@ int pkcs7_sig_note_pkey_algo(void *context, 
>> size_t hdrlen,
>>         ctx->sinfo->sig->pkey_algo = "rsa";
>>         ctx->sinfo->sig->encoding = "pkcs1";
>>         break;
>> +    case OID_id_ecdsa_with_sha256:
>> +        ctx->sinfo->sig->pkey_algo = "ecdsa";
>> +        ctx->sinfo->sig->encoding = "x962";
>> +        break;
>
> Hi Stefan,
>
> Does CONFIG_MODULE_SIG_KEY_TYPE_ECDSA have a dependency on 
> MODULE_SIG_SHA256?

You are right, per the code above it does have a dependency on SHA256. 
ECDSA is using NIST p384 (secp384r1) for signing and per my tests it can 
be paired with all the sha hashes once the code above is extended. Now 
when it comes to module signing, should we pair it with a particular 
hash? I am not currently aware of a guidance document on this but sha256 
and sha384 seem to be good choices these days, so maybe selecting ECDSA 
module signing should have a 'depends on' on these?

   Stefan