netdev - Re: [PATCH bpf-next v5 3/8] bpf: per-cgroup lsm flavor

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Message-ID: <20220426063024.4hkgajqzm6edf4u3@kafai-mbp.dhcp.thefacebook.com>
Date:   Mon, 25 Apr 2022 23:30:24 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org
Subject: Re: [PATCH bpf-next v5 3/8] bpf: per-cgroup lsm flavor

On Mon, Apr 25, 2022 at 11:27:08PM -0700, Martin KaFai Lau wrote:
> On Tue, Apr 19, 2022 at 12:00:48PM -0700, Stanislav Fomichev wrote:
> > Allow attaching to lsm hooks in the cgroup context.
> > 
> > Attaching to per-cgroup LSM works exactly like attaching
> > to other per-cgroup hooks. New BPF_LSM_CGROUP is added
> > to trigger new mode; the actual lsm hook we attach to is
> > signaled via existing attach_btf_id.
> > 
> > For the hooks that have 'struct socket' as its first argument,
> > we use the cgroup associated with that socket. For the rest,
> > we use 'current' cgroup (this is all on default hierarchy == v2 only).
> > Note that for the hooks that work on 'struct sock' we still
> > take the cgroup from 'current' because most of the time,
> > the 'sock' argument is not properly initialized.
> This paragraph is out-dated.
> 
> > Behind the scenes, we allocate a shim program that is attached
> > to the trampoline and runs cgroup effective BPF programs array.
> > This shim has some rudimentary ref counting and can be shared
> > between several programs attaching to the same per-cgroup lsm hook.
> > 
> > Note that this patch bloats cgroup size because we add 211
> > cgroup_bpf_attach_type(s) for simplicity sake. This will be
> > addressed in the subsequent patch.
> > 
> > Also note that we only add non-sleepable flavor for now. To enable
> > sleepable use-cases, BPF_PROG_RUN_ARRAY_CG has to grab trace rcu,
> s/BPF_PROG_RUN_ARRAY_CG/bpf_prog_run_array_cg/
> 
> > shim programs have to be freed via trace rcu, cgroup_bpf.effective
> > should be also trace-rcu-managed + maybe some other changes that
> > I'm not aware of.
Will continue the review tomorrow. thanks.