linux-kernel - Re: [RFC][PATCH 00/10] KEYS: Introduce user asymmetric keys and signatures

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Date:   Thu, 6 Jul 2023 16:27:09 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     dhowells@...hat.com, dwmw2@...radead.org,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        jarkko@...nel.org, song@...nel.org, jolsa@...nel.org,
        ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com,
        rostedt@...dmis.org, mhiramat@...nel.org, mykolal@...com,
        shuah@...nel.org, linux-kernel@...r.kernel.org,
        keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        bpf@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, pbrobinson@...il.com,
        zbyszek@...waw.pl, zohar@...ux.ibm.com,
        linux-integrity@...r.kernel.org, paul@...l-moore.com,
        linux-security-module@...r.kernel.org, wiktor@...acode.biz,
        devel@...ts.sequoia-pgp.org, gnupg-devel@...pg.org,
        ebiggers@...nel.org, Jason@...c4.com, mail@...iej.szmigiero.name,
        antony@...nard.ch, konstantin@...uxfoundation.org,
        James.Bottomley@...senpartnership.com,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [RFC][PATCH 00/10] KEYS: Introduce user asymmetric keys and
 signatures

On Thu, Jul 06, 2023 at 04:42:13PM +0200, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@...wei.com>
> 
> Define a new TLV-based format for keys and signatures, aiming to store and
> use in the kernel the crypto material from other unsupported formats
> (e.g. PGP).
> 
> TLV fields have been defined to fill the corresponding kernel structures
> public_key, public_key_signature and key_preparsed_payload.
> 
> Keys:
>                 struct public_key {     struct key_preparsed_payload {
> KEY_PUB       -->  void *key;
>                    u32 keylen;         --> prep->payload.data[asym_crypto]
> KEY_ALGO      -->  const char *pkey_algo;
> KEY_KID0
> KEY_KID1                               --> prep->payload.data[asym_key_ids]
> KEY_KID2  
> KEY_DESC                               --> prep->description
> 
> 
> Signatures:
>                 struct public_key_signature {
> SIG_S         -->  u8 *s;
>                    u32 s_size;
> SIG_KEY_ALGO  -->  const char *pkey_algo;
> SIG_HASH_ALGO -->  const char *hash_algo;
>                    u32 digest_size;
> SIG_ENC       -->  const char *encoding;   
> SIG_KID0
> SIG_KID1      -->  struct asymmetric_key_id *auth_ids[3];
> SIG_KID2  
> 
> 
> For keys, since the format conversion has to be done in user space, user
> space is assumed to be trusted, in this proposal. Without this assumption,
> a malicious conversion tool could make a user load to the kernel a
> different key than the one expected.
> 
> That should not be a particular problem for keys that are embedded in the
> kernel image and loaded at boot, since the conversion happens in a trusted
> environment such as the building infrastructure of the Linux distribution
> vendor.
> 
> In the other cases, such as enrolling a key through the Machine Owner Key
> (MOK) mechanism, the user is responsible to ensure that the crypto material
> carried in the original format remains the same after the conversion.
> 
> For signatures, assuming the strength of the crypto algorithms, altering
> the crypto material is simply a Denial-of-Service (DoS), as data can be
> validated only with the right signature.
> 
> 
> This patch set also offers the following contributions:
> 
> - An API similar to the PKCS#7 one, to verify the authenticity of system
>   data through user asymmetric keys and signatures
> 
> - A mechanism to store a keyring blob in the kernel image and to extract
>   and load the keys at system boot
>   
> - eBPF binding, so that data authenticity verification with user asymmetric
>   keys and signatures can be carried out also with eBPF programs

Nack to bpf bits.
You've convinced us that bpf_verify_pkcs7_signature() is what you need.
Yet, 9 month later there are no users of it and you came back with this new
bpf_verify_uasym_signature() helper that practically not much different.

Instead of brand new "public key info" format sign your rpms via
existing pkcs7 mechanism and verify with bpf_verify_pkcs7_signature().