linux-kernel - Re: [PATCH sched_ext/for-6.15 v3 3/5] sched_ext: Add scx_kfunc_ids_ops_context_sensitive for unified filtering of context-sensitive SCX kfuncs

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Message-ID: <Z8IrGagRhkHlUejz@slm.duckdns.org>
Date: Fri, 28 Feb 2025 11:31:05 -1000
From: Tejun Heo <tj@...nel.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Juntong Deng <juntong.deng@...look.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Eddy Z <eddyz87@...il.com>,
	Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Kumar Kartikeya Dwivedi <memxor@...il.com>,
	David Vernet <void@...ifault.com>, Andrea Righi <arighi@...dia.com>,
	Changwoo Min <changwoo@...lia.com>, bpf <bpf@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH sched_ext/for-6.15 v3 3/5] sched_ext: Add
 scx_kfunc_ids_ops_context_sensitive for unified filtering of
 context-sensitive SCX kfuncs

Hello,

On Thu, Feb 27, 2025 at 06:34:37PM -0800, Alexei Starovoitov wrote:
> > Hmm... would that mean a non-sched_ext bpf prog would be able to call e.g.
> > scx_bpf_dsq_insert()?
> 
> Not as far as I can tell.
> scx_kfunc_ids_unlocked[] doesn't include scx_bpf_dsq_insert.
> It's part of scx_kfunc_ids_enqueue_dispatch[].
> 
> So this bit in patch 3 enables it:
> +       if ((flags & SCX_OPS_KF_ENQUEUE) &&
> +           btf_id_set8_contains(&scx_kfunc_ids_enqueue_dispatch, kfunc_id))
> 
> and in patch 2:
> +       [SCX_OP_IDX(enqueue)]                   = SCX_OPS_KF_ENQUEUE,
> 
> So scx_bpf_dsq_insert() kfunc can only be called out
> of enqueue() sched-ext hook.
> 
> So the restriction is still the same. afaict.

Hmm... maybe I'm missing something:

  static int scx_kfunc_ids_ops_context_sensitive_filter(const struct bpf_prog *prog, u32 kfunc_id)
  {
         u32 moff, flags;

         // allow non-context sensitive kfuncs
         if (!btf_id_set8_contains(&scx_kfunc_ids_ops_context_sensitive, kfunc_id))
                 return 0;

         // allow unlocked to be called form all SYSCALL progs
         if (prog->type == BPF_PROG_TYPE_SYSCALL &&
             btf_id_set8_contains(&scx_kfunc_ids_unlocked, kfunc_id))
                 return 0;

         // *** HERE, allow if the prog is not SCX ***
         if (prog->type == BPF_PROG_TYPE_STRUCT_OPS &&
             prog->aux->st_ops != &bpf_sched_ext_ops)
                 return 0;

         /* prog->type == BPF_PROG_TYPE_STRUCT_OPS && prog->aux->st_ops == &bpf_sched_ext_ops*/

         // other context sensitive allow's

So, I think it'd say yes if a non-SCX BPF prog tries to call a context
sensitive SCX kfunc.

Thanks.

-- 
tejun