From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="BjaH4eQH" Received: from mail-ej1-x62d.google.com (mail-ej1-x62d.google.com [IPv6:2a00:1450:4864:20::62d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69E14125 for ; Sat, 2 Dec 2023 11:19:47 -0800 (PST) Received: by mail-ej1-x62d.google.com with SMTP id a640c23a62f3a-9fa45e75ed9so465007666b.1 for ; Sat, 02 Dec 2023 11:19:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1701544785; x=1702149585; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=CVnD9IBKgeFXP1N/4EisJqwdjkIdWjmpXDkOaU1l2H0=; b=BjaH4eQHgwykQaCIrUp7JJdBLEyVwWOiqbCi9YFduGND0fKrr4fvqVG4V2UKMX9dZZ Rp8uNNpMjVa90GJWFMMOfYQGOGsYeldHByy+nnmT6kXSIP+lNJBUZKKrO4sTkucEu1fa iHev37Iid4BNdH+yQ/YkCMxeJmSZpDBslGndj0Fzm6l6IkrlaCibKDaUW2ojEChVxW4O qlIkFGH8WwOMP399ry2a7ITZkrISIvT00Dy5RB6+dwj14NRlTyFcZhwMXn1pO/NHb0RL W+jzH4mKIAHAhhs10hUU/7CPN+9DOL0dPUc7YiURTQXmvHifijHyr8klepO5QAZqoQQA oHew== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701544785; x=1702149585; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=CVnD9IBKgeFXP1N/4EisJqwdjkIdWjmpXDkOaU1l2H0=; b=JFsWYXKBB7jGyzVB5YF2IVlRFNSH6wthfxCCgTp80cmZ90H4nMsxt+9MXb139AH1Vc kPijmYqEVDbPtB5h33lBHoTdyJnfhuScSlRp+tXKklMYwq0LXVf2JmzyoSYzCmAGqM+H BKenRgXluRBF06tMx5eDP0EOtKOm2+4d5ybTLQsPokfiydVHzOOJcj0NtiDb31+8CtA/ SBCDY53xOUOoVxy2CIz2bY3bgLF2z+2/D2j/ORwrfW2Xww1JINzAt7QzvcQwVlbc+0fu dm50XB3M7F8fRNPdOh/fp7qV8Z21QsZw9/mG7y+ZfmnFsF5+GL8UdHK9Ondn06KNPN0z MI2Q== X-Gm-Message-State: AOJu0YyPHb+eBnfWFUizywUG5DWL9srpfJUuOb+JPFYg+kjsVytuNiWZ QOufLYJpBVY8Hlt9awJCg95aCg1scHzkIw== X-Google-Smtp-Source: AGHT+IGdO+iRzWWumSEC+qjIegMz38ZOfYsI3AGMCOWLKkWpKeeCZCjwgahwhUnzsa0p6udFEbauyg== X-Received: by 2002:a17:906:20d9:b0:9d4:2080:61dc with SMTP id c25-20020a17090620d900b009d4208061dcmr2083865ejc.22.1701544785350; Sat, 02 Dec 2023 11:19:45 -0800 (PST) Received: from localhost.localdomain ([2a00:20:6008:6fb9:fa16:54ff:fe6e:2940]) by smtp.gmail.com with ESMTPSA id i23-20020a170906115700b00a18ed83ce42sm3127814eja.15.2023.12.02.11.19.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 02 Dec 2023 11:19:45 -0800 (PST) From: Dmitrii Dolgov <9erthalion6@gmail.com> To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, dan.carpenter@linaro.org, olsajiri@gmail.com, asavkov@redhat.com, Dmitrii Dolgov <9erthalion6@gmail.com> Subject: [PATCH bpf-next v6 1/4] bpf: Relax tracing prog recursive attach rules Date: Sat, 2 Dec 2023 20:15:47 +0100 Message-ID: <20231202191556.30997-2-9erthalion6@gmail.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20231202191556.30997-1-9erthalion6@gmail.com> References: <20231202191556.30997-1-9erthalion6@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Currently, it's not allowed to attach an fentry/fexit prog to another one fentry/fexit. At the same time it's not uncommon to see a tracing program with lots of logic in use, and the attachment limitation prevents usage of fentry/fexit for performance analysis (e.g. with "bpftool prog profile" command) in this case. An example could be falcosecurity libs project that uses tp_btf tracing programs. Following the corresponding discussion [1], the reason for that is to avoid tracing progs call cycles without introducing more complex solutions. But currently it seems impossible to load and attach tracing programs in a way that will form such a cycle. The limitation is coming from the fact that attach_prog_fd is specified at the prog load (thus making it impossible to attach to a program loaded after it in this way), as well as tracing progs not implementing link_detach. Replace "no same type" requirement with verification that no more than one level of attachment nesting is allowed. In this way only one fentry/fexit program could be attached to another fentry/fexit to cover profiling use case, and still no cycle could be formed. To implement, add a new field into bpf_prog_aux to track the depth of attachment. [1]: https://lore.kernel.org/bpf/20191108064039.2041889-16-ast@kernel.org/ Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com> --- Previous discussion: https://lore.kernel.org/bpf/20231201154734.8545-1-9erthalion6@gmail.com/ Changes in v6: - Apply nesting level limitation only to tracing programs, otherwise it's possible to apply it in "fentry->extension" case and break it Changes in v5: - Remove follower_cnt and drop unreachable cycle prevention condition - Allow only one level of attachment nesting - Do not display attach_depth in bpftool, as it doesn't make sense anymore Changes in v3: - Fix incorrect decreasing of attach_depth, setting to 0 instead - Place bookkeeping later, to not miss a cleanup if needed - Display attach_depth in bpftool only if the value is not 0 Changes in v2: - Verify tgt_prog is not null - Replace boolean followed with number of followers, to handle multiple progs attaching/detaching include/linux/bpf.h | 1 + include/uapi/linux/bpf.h | 1 + kernel/bpf/syscall.c | 12 ++++++++++++ kernel/bpf/verifier.c | 33 +++++++++++++++++++-------------- tools/include/uapi/linux/bpf.h | 1 + 5 files changed, 34 insertions(+), 14 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index eb447b0a9423..1588e48fe31c 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1400,6 +1400,7 @@ struct bpf_prog_aux { u32 real_func_cnt; /* includes hidden progs, only used for JIT and freeing progs */ u32 func_idx; /* 0 for non-func prog, the index in func array for func prog */ u32 attach_btf_id; /* in-kernel BTF type id to attach to */ + u32 attach_depth; /* for tracing prog, level of attachment nesting */ u32 ctx_arg_info_size; u32 max_rdonly_access; u32 max_rdwr_access; diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index e88746ba7d21..9cf45ad914f1 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -6468,6 +6468,7 @@ struct bpf_prog_info { __u32 verified_insns; __u32 attach_btf_obj_id; __u32 attach_btf_id; + __u32 attach_depth; } __attribute__((aligned(8))); struct bpf_map_info { diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 5e43ddd1b83f..9c56b5970d7e 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3039,6 +3039,7 @@ static void bpf_tracing_link_release(struct bpf_link *link) bpf_trampoline_put(tr_link->trampoline); + link->prog->aux->attach_depth = 0; /* tgt_prog is NULL if target is a kernel function */ if (tr_link->tgt_prog) bpf_prog_put(tr_link->tgt_prog); @@ -3243,6 +3244,16 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog, goto out_unlock; } + if (tgt_prog) { + /* Bookkeeping for managing the prog attachment chain. If it's a + * tracing program, bump the level, otherwise carry it on. + */ + if (prog->type == BPF_PROG_TYPE_TRACING) + prog->aux->attach_depth = tgt_prog->aux->attach_depth + 1; + else + prog->aux->attach_depth = tgt_prog->aux->attach_depth; + } + link->tgt_prog = tgt_prog; link->trampoline = tr; @@ -4510,6 +4521,7 @@ static int bpf_prog_get_info_by_fd(struct file *file, if (prog->aux->btf) info.btf_id = btf_obj_id(prog->aux->btf); info.attach_btf_id = prog->aux->attach_btf_id; + info.attach_depth = prog->aux->attach_depth; if (attach_btf) info.attach_btf_obj_id = btf_obj_id(attach_btf); diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8e7b6072e3f4..a3ea2087a6b2 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -20109,6 +20109,11 @@ int bpf_check_attach_target(struct bpf_verifier_log *log, if (tgt_prog) { struct bpf_prog_aux *aux = tgt_prog->aux; + if (aux->attach_depth >= 1) { + bpf_log(log, "Cannot attach with more than one level of nesting\n"); + return -EINVAL; + } + if (bpf_prog_is_dev_bound(prog->aux) && !bpf_prog_dev_bound_match(prog, tgt_prog)) { bpf_log(log, "Target program bound device mismatch"); @@ -20147,10 +20152,11 @@ int bpf_check_attach_target(struct bpf_verifier_log *log, bpf_log(log, "Can attach to only JITed progs\n"); return -EINVAL; } - if (tgt_prog->type == prog->type) { - /* Cannot fentry/fexit another fentry/fexit program. - * Cannot attach program extension to another extension. - * It's ok to attach fentry/fexit to extension program. + if (tgt_prog->type == prog->type && prog_extension) { + /* + * To avoid potential call chain cycles, prevent attaching of a + * program extension to another extension. It's ok to attach + * fentry/fexit to extension program. */ bpf_log(log, "Cannot recursively attach\n"); return -EINVAL; @@ -20163,16 +20169,15 @@ int bpf_check_attach_target(struct bpf_verifier_log *log, * except fentry/fexit. The reason is the following. * The fentry/fexit programs are used for performance * analysis, stats and can be attached to any program - * type except themselves. When extension program is - * replacing XDP function it is necessary to allow - * performance analysis of all functions. Both original - * XDP program and its program extension. Hence - * attaching fentry/fexit to BPF_PROG_TYPE_EXT is - * allowed. If extending of fentry/fexit was allowed it - * would be possible to create long call chain - * fentry->extension->fentry->extension beyond - * reasonable stack size. Hence extending fentry is not - * allowed. + * type. When extension program is replacing XDP function + * it is necessary to allow performance analysis of all + * functions. Both original XDP program and its program + * extension. Hence attaching fentry/fexit to + * BPF_PROG_TYPE_EXT is allowed. If extending of + * fentry/fexit was allowed it would be possible to create + * long call chain fentry->extension->fentry->extension + * beyond reasonable stack size. Hence extending fentry + * is not allowed. */ bpf_log(log, "Cannot extend fentry/fexit\n"); return -EINVAL; diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index e88746ba7d21..9cf45ad914f1 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -6468,6 +6468,7 @@ struct bpf_prog_info { __u32 verified_insns; __u32 attach_btf_obj_id; __u32 attach_btf_id; + __u32 attach_depth; } __attribute__((aligned(8))); struct bpf_map_info { -- 2.41.0