linux-kernel - Re: [RFC] security: replace indirect calls with static calls

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Message-ID: <YB1m2i6bUM0LO5wS@hirez.programming.kicks-ass.net>
Date:   Fri, 5 Feb 2021 16:40:10 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Brendan Jackman <jackmanb@...omium.org>,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Paul Renauld <renauld@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        James Morris <jmorris@...ei.org>, pjt@...gle.com,
        jannh@...gle.com, rafael.j.wysocki@...el.com,
        keescook@...omium.org, thgarnie@...omium.org, kpsingh@...gle.com,
        paul.renauld.epfl@...il.com, Brendan Jackman <jackmanb@...gle.com>,
        rostedt@...dmis.org
Subject: Re: [RFC] security: replace indirect calls with static calls

On Fri, Feb 05, 2021 at 10:09:26AM -0500, Mathieu Desnoyers wrote:
> Then we should be able to generate the following using static keys as a
> jump table and N static calls:
> 
>   jump <static key label target>
> label_N:
>   stack setup
>   call
> label_N-1:
>   stack setup
>   call
> label_N-2:
>   stack setup
>   call
>   ...
> label_0:
>   jump end
> label_fallback:
>   <iteration and indirect calls>
> end:
> 
> So the static keys would be used to jump to the appropriate label (using
> a static branch, which has pretty much 0 overhead). Static calls would
> be used to implement each of the calls.
> 
> Thoughts ?

At some point I tried to extend the static_branch infra to do multiple
targets and while the low level plumbing is trivial, I ran into trouble
trying to get a sane C level API for it.