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

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Message-ID: <YIAf9jYGu03lrJLn@gunter>
Date:   Wed, 21 Apr 2021 14:52:06 +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 [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.

Thanks!

Jessica