From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53AC9C433EF for ; Tue, 10 May 2022 17:31:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348237AbiEJRfK (ORCPT ); Tue, 10 May 2022 13:35:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57850 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241327AbiEJRfJ (ORCPT ); Tue, 10 May 2022 13:35:09 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E8DE36173 for ; Tue, 10 May 2022 10:31:08 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id g129-20020a25db87000000b0064b0d671050so2351954ybf.6 for ; Tue, 10 May 2022 10:31:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=+OItLiQE6V8bbnL9yESMNsFuPWf1H2cgWOWhkugLbts=; b=C7uHnMQH/g8c4RQwEgQXe4iSngwlEhlbNu8w8o2e9ZZmCvYNC6h/ztU1TomM1+2+pU 5w6ss35/qQ8cdqeviXf88HW9jauycb9ePQV5jBs5xWONQdJlDCcFle9WlKJlTxrxI+cq igyaKezOXn17wIMFftdSC2GmAmyb6RyjkcdlgAJ+XNUwZDnQWJV37t5qR5rEGTv2Nk2i fJ1M2tkbFQV2scAO5/E0MfqdDmGR5HSZt6Wi6KaTLRcK2DaTVXuZuLUNzyHaqxhZS1B9 1NtWUdFoiiqselXALoSIBxFznLhceBwgbUDXiL30pb93svi0tSMUfDOB/iDNA5C+kDtU Y6ow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=+OItLiQE6V8bbnL9yESMNsFuPWf1H2cgWOWhkugLbts=; b=xZh3h4iPiDTcSxCqu7YAsykp84Bd33rxOchoS+ghYOhyg50CEcVKaVVXLYVly6aThl 6evbrch5yzJL3/Ti5rkGCvGCX4ORSxiGBist3wPKst+3xcqNFa+Q10tteji3aSqyF75/ UACQ0ycX4jh5TVgREohzLCU3uCz505A7JXlNE/GNOi9j6Jd4WwvlPQrJfJN2gMDlh/gD QoIsFJf5/Yqs822rJZkxfwSKFVoMjN/7A1TgehmTg5uyPTL3Z8NFCyBI8y5W6/Bx1BYN HT1WtsjCd887EcMa+ZHDEEdNVJWeSqJ/GaWbbKR1+eNy2MuVscz+kuuyyce1RGNjvDtl kFtg== X-Gm-Message-State: AOAM531Iquv9XHH7++76Yp+wSJEebkjw6wFSu6Sb0qmfTF+hKfkigik6 suDTEP+YCue0s7s8D0EaHTLoLQs= X-Google-Smtp-Source: ABdhPJzn7uyZpM0TZ1IyM3QlV/L2ZjzJjdOoEArLgCgMJaHR3V0/cutOa8vWeP+TULrBJY7f1Ragtr0= X-Received: from sdf2.svl.corp.google.com ([2620:15c:2c4:201:e4f0:6894:4cb0:4ccc]) (user=sdf job=sendgmr) by 2002:a25:e056:0:b0:645:d68d:8474 with SMTP id x83-20020a25e056000000b00645d68d8474mr19379979ybg.294.1652203867668; Tue, 10 May 2022 10:31:07 -0700 (PDT) Date: Tue, 10 May 2022 10:31:05 -0700 In-Reply-To: <20220510050546.tpuslkld4rlrqexp@MBP-98dd607d3435.dhcp.thefacebook.com> Message-Id: Mime-Version: 1.0 References: <20220429211540.715151-1-sdf@google.com> <20220429211540.715151-5-sdf@google.com> <20220510050546.tpuslkld4rlrqexp@MBP-98dd607d3435.dhcp.thefacebook.com> Subject: Re: [PATCH bpf-next v6 04/10] bpf: minimize number of allocated lsm slots per program From: sdf@google.com To: Alexei Starovoitov Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org Content-Type: text/plain; charset="UTF-8"; format=flowed; delsp=yes Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 05/09, Alexei Starovoitov wrote: > On Fri, Apr 29, 2022 at 02:15:34PM -0700, Stanislav Fomichev wrote: > > Previous patch adds 1:1 mapping between all 211 LSM hooks > > and bpf_cgroup program array. Instead of reserving a slot per > > possible hook, reserve 10 slots per cgroup for lsm programs. > > Those slots are dynamically allocated on demand and reclaimed. > > > > It should be possible to eventually extend this idea to all hooks if > > the memory consumption is unacceptable and shrink overall effective > > programs array. > > > > struct cgroup_bpf { > > struct bpf_prog_array * effective[33]; /* 0 264 */ > > /* --- cacheline 4 boundary (256 bytes) was 8 bytes ago --- */ > > struct hlist_head progs[33]; /* 264 264 */ > > /* --- cacheline 8 boundary (512 bytes) was 16 bytes ago --- */ > > u8 flags[33]; /* 528 33 */ > > > > /* XXX 7 bytes hole, try to pack */ > > > > struct list_head storages; /* 568 16 */ > > /* --- cacheline 9 boundary (576 bytes) was 8 bytes ago --- */ > > struct bpf_prog_array * inactive; /* 584 8 */ > > struct percpu_ref refcnt; /* 592 16 */ > > struct work_struct release_work; /* 608 72 */ > > > > /* size: 680, cachelines: 11, members: 7 */ > > /* sum members: 673, holes: 1, sum holes: 7 */ > > /* last cacheline: 40 bytes */ > > }; > > > > Signed-off-by: Stanislav Fomichev > > --- > > include/linux/bpf-cgroup-defs.h | 3 +- > > include/linux/bpf_lsm.h | 6 -- > > kernel/bpf/bpf_lsm.c | 5 -- > > kernel/bpf/cgroup.c | 107 +++++++++++++++++++++++++++----- > > 4 files changed, 94 insertions(+), 27 deletions(-) > > > > diff --git a/include/linux/bpf-cgroup-defs.h > b/include/linux/bpf-cgroup-defs.h > > index d5a70a35dace..359d3f16abea 100644 > > --- a/include/linux/bpf-cgroup-defs.h > > +++ b/include/linux/bpf-cgroup-defs.h > > @@ -10,7 +10,8 @@ > > > > struct bpf_prog_array; > > > > -#define CGROUP_LSM_NUM 211 /* will be addressed in the next patch */ > > +/* Maximum number of concurrently attachable per-cgroup LSM hooks. */ > > +#define CGROUP_LSM_NUM 10 > > > > enum cgroup_bpf_attach_type { > > CGROUP_BPF_ATTACH_TYPE_INVALID = -1, > > diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h > > index 7f0e59f5f9be..613de44aa429 100644 > > --- a/include/linux/bpf_lsm.h > > +++ b/include/linux/bpf_lsm.h > > @@ -43,7 +43,6 @@ extern const struct bpf_func_proto > bpf_inode_storage_delete_proto; > > void bpf_inode_storage_free(struct inode *inode); > > > > int bpf_lsm_find_cgroup_shim(const struct bpf_prog *prog, bpf_func_t > *bpf_func); > > -int bpf_lsm_hook_idx(u32 btf_id); > > > > #else /* !CONFIG_BPF_LSM */ > > > > @@ -74,11 +73,6 @@ static inline int bpf_lsm_find_cgroup_shim(const > struct bpf_prog *prog, > > return -ENOENT; > > } > > > > -static inline int bpf_lsm_hook_idx(u32 btf_id) > > -{ > > - return -EINVAL; > > -} > > - > > #endif /* CONFIG_BPF_LSM */ > > > > #endif /* _LINUX_BPF_LSM_H */ > > diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c > > index a0e68ef5dfb1..1079c747e061 100644 > > --- a/kernel/bpf/bpf_lsm.c > > +++ b/kernel/bpf/bpf_lsm.c > > @@ -91,11 +91,6 @@ int bpf_lsm_find_cgroup_shim(const struct bpf_prog > *prog, > > return 0; > > } > > > > -int bpf_lsm_hook_idx(u32 btf_id) > > -{ > > - return btf_id_set_index(&bpf_lsm_hooks, btf_id); > > -} > > - > > int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog, > > const struct bpf_prog *prog) > > { > > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c > > index 9cc38454e402..787ff6cf8d42 100644 > > --- a/kernel/bpf/cgroup.c > > +++ b/kernel/bpf/cgroup.c > > @@ -79,10 +79,13 @@ unsigned int __cgroup_bpf_run_lsm_sock(const void > *ctx, > > shim_prog = (const struct bpf_prog *)((void *)insn - offsetof(struct > bpf_prog, insnsi)); > > > > cgrp = sock_cgroup_ptr(&sk->sk_cgrp_data); > > - if (likely(cgrp)) > > + if (likely(cgrp)) { > > + rcu_read_lock(); /* See bpf_lsm_attach_type_get(). */ > I've looked at bpf_lsm_attach_type_get/put, but still don't get it :) > shim_prog->aux->cgroup_atype stays the same for the life of shim_prog. > atype_usecnt will go up and down, but atype_usecnt == 0 is the only > interesting one from the pov of selecting atype in _get(). > And there shim_prog will be detached and trampoline destroyed. > The shim_prog->aux->cgroup_atype deref below cannot be happening on > freed shim_prog. > So what is the point of this critical section and sync_rcu() ? > It seems none of it is necessary. I was trying to guard against the reuse of the same cgroup_atype: CPU0 CPU1 __cgroup_bpf_run_lsm_socket: atype = shim_prog->aux->cgroup_atype __cgroup_bpf_detach bpf_lsm_attach_type_put(shim_prog attach_btf_id) __cgroup_bpf_attach(another hook) bpf_lsm_attach_type_get(another btf_id) ^^^ can reuse the same cgroup_atype array = cgrp->effective[atype] ^^^ run effective from another btf_id? So I added that sync_rcu to wait for existing shim_prog users to exit. Am I too paranoid? Maybe if I move bpf_lsm_attach_type_put deep into bpf_prog_put (deferred path) that won't be an issue and we can drop rcu_sync+read lock? > > It should be possible to eventually extend this idea to all hooks if > > the memory consumption is unacceptable and shrink overall effective > > programs array. > if BPF_LSM_CGROUP do atype differently looks too special. > Why not to do this generalization right now? > Do atype_get for all cgroup hooks and get rid of > to_cgroup_bpf_attach_type ? > Combine ranges of attach_btf_id for lsm_cgroup and enum bpf_attach_type > for traditional cgroup hooks into single _get() method that returns a slot > in effective[] array ? > attach/detach/query apis won't notice this internal implementation detail. I'm being extra cautious by using this new allocation scheme for LSM only. If there is no general pushback, I can try to convert everything at the same time.