From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Stanislav Fomichev <sdf@google.com>
Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, ast@kernel.org,
daniel@iogearbox.net, andrii@kernel.org
Subject: Re: [RFC bpf-next 1/4] bpf: cgroup_sock lsm flavor
Date: Wed, 16 Feb 2022 18:38:49 -0800 [thread overview]
Message-ID: <20220217023849.jn5pcwz23rj2772x@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20220216001241.2239703-2-sdf@google.com>
On Tue, Feb 15, 2022 at 04:12:38PM -0800, Stanislav Fomichev wrote:
> {
> @@ -1767,14 +1769,23 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
>
> /* arg1: lea rdi, [rbp - stack_size] */
> EMIT4(0x48, 0x8D, 0x7D, -stack_size);
> - /* arg2: progs[i]->insnsi for interpreter */
> - if (!p->jited)
> - emit_mov_imm64(&prog, BPF_REG_2,
> - (long) p->insnsi >> 32,
> - (u32) (long) p->insnsi);
> - /* call JITed bpf program or interpreter */
> - if (emit_call(&prog, p->bpf_func, prog))
> - return -EINVAL;
> +
> + if (p->expected_attach_type == BPF_LSM_CGROUP_SOCK) {
> + /* arg2: progs[i] */
> + emit_mov_imm64(&prog, BPF_REG_2, (long) p >> 32, (u32) (long) p);
> + if (emit_call(&prog, __cgroup_bpf_run_lsm_sock, prog))
> + return -EINVAL;
> + } else {
> + /* arg2: progs[i]->insnsi for interpreter */
> + if (!p->jited)
> + emit_mov_imm64(&prog, BPF_REG_2,
> + (long) p->insnsi >> 32,
> + (u32) (long) p->insnsi);
> +
> + /* call JITed bpf program or interpreter */
> + if (emit_call(&prog, p->bpf_func, prog))
> + return -EINVAL;
Overall I think it's a workable solution.
As far as mechanism I think it would be better
to allocate single dummy bpf_prog and use normal fmod_ret
registration mechanism instead of hacking arch trampoline bits.
Set dummy_bpf_prog->bpf_func = __cgroup_bpf_run_lsm_sock;
and keep as dummy_bpf_prog->jited = false;
From p->insnsi pointer in arg2 it's easy to go back to struct bpf_prog.
Such dummy prog might even be statically defined like dummy_bpf_prog.
Or allocated dynamically once.
It can be added as fmod_ret to multiple trampolines.
Just gut the func_model check.
As far as api the attach should probably be to a cgroup+lsm_hook pair.
link_create.target_fd will be cgroup_fd.
At prog load time attach_btf_id should probably be one
of existing bpf_lsm_* hooks.
Feels wrong to duplicate the whole set into lsm_cgroup_sock set.
It's fine to have prog->expected_attach_type == BPF_LSM_CGROUP_SOCK
to disambiguate. Will we probably only have two:
BPF_LSM_CGROUP_SOCK and BPF_LSM_CGROUP_TASK ?
> +int __cgroup_bpf_run_lsm_sock(u64 *regs, const struct bpf_prog *prog)
> +{
> + struct socket *sock = (void *)regs[BPF_REG_0];
> + struct cgroup *cgrp;
> + struct sock *sk;
> +
> + sk = sock->sk;
> + if (!sk)
> + return 0;
> +
> + cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data);
> +
> + return BPF_PROG_RUN_ARRAY_CG(cgrp->bpf.effective[prog->aux->cgroup_atype],
> + regs, bpf_prog_run, 0);
> +}
Would it be fast enough?
We went through a bunch of optimization for normal cgroup and ended with:
if (cgroup_bpf_enabled(CGROUP_INET_INGRESS) &&
cgroup_bpf_sock_enabled(sk, CGROUP_INET_INGRESS))
Here the trampoline code plus call into __cgroup_bpf_run_lsm_sock
will be there for all cgroups.
Since cgroup specific check will be inside BPF_PROG_RUN_ARRAY_CG.
I suspect it's ok, since the link_create will be for few specific lsm hooks
which are typically not in the fast path.
Unlike traditional cgroup hook like ingress that is hot.
For BPF_LSM_CGROUP_TASK it will take cgroup from current instead of sock, right?
Args access should magically work. 'regs' above should be fine for
all lsm hooks.
The typical prog:
+SEC("lsm_cgroup_sock/socket_post_create")
+int BPF_PROG(socket_post_create, struct socket *sock, int family,
+ int type, int protocol, int kern)
looks good too.
Feel natural.
I guess they can be sleepable too?
next prev parent reply other threads:[~2022-02-17 2:38 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-16 0:12 [RFC bpf-next 0/4] bpf: cgroup_sock lsm flavor Stanislav Fomichev
2022-02-16 0:12 ` [RFC bpf-next 1/4] " Stanislav Fomichev
2022-02-17 2:38 ` Alexei Starovoitov [this message]
2022-02-17 16:21 ` sdf
2022-02-17 16:58 ` Alexei Starovoitov
2022-02-16 0:12 ` [RFC bpf-next 2/4] bpf: allow writing to sock->sk_priority from lsm progtype Stanislav Fomichev
2022-02-16 0:12 ` [RFC bpf-next 3/4] libbpf: add lsm_cgoup_sock type Stanislav Fomichev
2022-02-16 0:12 ` [RFC bpf-next 4/4] selftest: lsm_cgroup_sock sample usage Stanislav Fomichev
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