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Date:   Fri, 5 Feb 2021 16:40:10 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Brendan Jackman <jackmanb@chromium.org>,
        linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
        linux-security-module@vger.kernel.org,
        Paul Renauld <renauld@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        James Morris <jmorris@namei.org>, pjt@google.com,
        jannh@google.com, rafael.j.wysocki@intel.com,
        keescook@chromium.org, thgarnie@chromium.org, kpsingh@google.com,
        paul.renauld.epfl@gmail.com, Brendan Jackman <jackmanb@google.com>,
        rostedt@goodmis.org
Subject: Re: [RFC] security: replace indirect calls with static calls
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References: <20200820164753.3256899-1-jackmanb@chromium.org>
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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.