netdev - Re: [RFC PATCH] rxrpc: Fix -Wframe-larger-than= warnings from on-stack crypto

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Message-ID: <21523.1564064970@warthog.procyon.org.uk>
Date:   Thu, 25 Jul 2019 15:29:30 +0100
From:   David Howells <dhowells@...hat.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        Arnd Bergmann <arnd@...db.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        "<netdev@...r.kernel.org>" <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH] rxrpc: Fix -Wframe-larger-than= warnings from on-stack crypto

Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote:

> Given that this part of the driver only uses synchronous crypto, and
> only using a hardcoded algo and mode [pcbc(fcrypt)], of which only a
> generic C implementation exists, may I suggest that we switch to a
> library based approach instead?
> 
> That way, we can get rid of the crypto API overhead here, and IMO, we
> can drop support for this cipher from the crypto API entirely.

Ummm...  I'm not entirely sure.  At some point, I need to look at implementing
the rxgk security class to allow gss to be used.  That can in theory support
any kerberos cipher suite (which don't include pcbc or fcrypt).  I don't yet
know how much code I could theoretically share with rxkad.c.

However, since pcbc and fcrypt are only used by rxkad.c, it might make sense
to move them to net/rxrpc/ and hard code them in rxkad.c - though I'd prefer
to make an attempt on rxgk first.

David