netdev - Re: [PATCH RFC v1 1/3] bpf: move from sha1 to blake2s in tag calculation

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Date:   Wed, 12 Jan 2022 17:33:44 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ardb@...nel.org>,
        Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH RFC v1 1/3] bpf: move from sha1 to blake2s in tag calculation

On Wed, Jan 12, 2022 at 5:14 PM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> [ adding the bpf list - please make sure to include that when sending
>   BPF-related patches, not everyone in BPF land follows netdev ]
>
> "Jason A. Donenfeld" <Jason@...c4.com> writes:
>
> > BLAKE2s is faster and more secure. SHA-1 has been broken for a long time
> > now. This also removes quite a bit of code, and lets us potentially
> > remove sha1 from lib, which would further reduce vmlinux size.
>
> AFAIU, the BPF tag is just used as an opaque (i.e., arbitrary) unique
> identifier for BPF programs, without any guarantees of stability. Which
> means changing it should be fine; at most we'd confuse some operators
> who have memorised the tags of their BPF programs :)
>
> The only other concern I could see would be if it somehow locked us into
> that particular algorithm for other future use cases for computing
> hashes of BPF programs (say, signing if that ends up being the direction
> we go in). But obviously SHA1 would not be a good fit for that anyway,
> so the algorithm choice would have to be part of that discussion in any
> case.
>
> So all in all, I don't see any issues with making this change for BPF.

Nack.
It's part of api. We cannot change it.