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

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Date:   Wed, 21 Apr 2021 14:58:05 +0200
From:   Jessica Yu <jeyu@...nel.org>
To:     Stefan Berger <stefanb@...ux.ibm.com>
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

+++ Stefan Berger [21/04/21 08:54 -0400]:
>
>On 4/21/21 8:52 AM, Jessica Yu wrote:
>>+++ Stefan Berger [20/04/21 17:02 -0400]:
>>>
>>>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?
>>
>>Yeah, I would tack on the 'depends on' until the code above has been
>>extended to cover more sha hashes - because currently if someone
>>builds and signs a bunch of modules with an ECDSA key, they will fail
>>to load if they picked something other than sha256. I am unfortunately
>>not knowledgeable enough to suggest an official guideline on choice of
>>hash, but for now it is reasonable to have a 'depends on' for which
>>hashes the code currently supports, so that users don't run into
>>module loading rejection issues.
>
>
>I was going to repost this series now with the additional OIDs 
>supported above and a recommendation to use sha384 in the help text 
>for ECDSA-signed modules, but not enforcing this but instead trusting 
>the user that they will choose a reasonable hash (probably >= sha256).

OK, that sounds good to me.

Thanks Stefan!