From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1DA4870814 for ; Fri, 11 Jul 2025 03:10:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752203441; cv=none; b=AF8zCSCd9iP/6z74qthAKjUYc0k3KloVZ3tDLNvscMw0hicDkuzDZE8IMLnzZiY9sSEETkOAIpZ2kvK0B6+AzDzUwVuHSkQi9PTRbB8Wv5MJ7SPAGNOHoorNVxkndTgOL8/ANpIYEdtSRLir7ciGpMJ8xdi/hdnV6iXFf8fCqMA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752203441; c=relaxed/simple; bh=/m17edC0OXP7hMTmCRLK1oCb0lUyP4ccJ96sraTED0g=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=QHxovLyM9451qGfKkwypZHyZGLMYnd3kjwKxmeM75IXMIE6V+mawE37Wft3MzYWK1+w6sREH5pKy7R9WhEsbgVKd9QeD6Bgtj61P7LnBA07YW0jmf148uL7Rn/B4IJZ0JlsGwjjIHOIJYOnc7UmUZFpN8i2vGqPssRbFqmgUvQ8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=B0/4L3o0; arc=none smtp.client-ip=95.215.58.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="B0/4L3o0" Message-ID: <2f8c792e-9675-4385-b1cb-10266c72bd45@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1752203437; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=x715/q+udRUTDW1yuo6mapYClglFmqiiqnYPKulS+Uk=; b=B0/4L3o0Y6gI127BGVHuDHtJFgF+AxSK2e2eboTSclO75hweb+vut+vpNNJR0+esORmOPb iEzHQKXsRD4WUJxU4FoQIvmtDPHMlD0rDq/RBXuITDuBKj14rkWE+7GqABcvUk9dgiFL3j zgN0h/yLXpvQgYFr0YdjzuOlCZMA2PI= Date: Thu, 10 Jul 2025 20:10:29 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v3] bpf: make the attach target more accurate Content-Language: en-GB To: Menglong Dong , ast@kernel.org, daniel@iogearbox.net Cc: john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Menglong Dong References: <20250710070835.260831-1-dongml2@chinatelecom.cn> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <20250710070835.260831-1-dongml2@chinatelecom.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 7/10/25 12:08 AM, Menglong Dong wrote: > For now, we lookup the address of the attach target in > bpf_check_attach_target() with find_kallsyms_symbol_value or > kallsyms_lookup_name, which is not accurate in some cases. > > For example, we want to attach to the target "t_next", but there are > multiple symbols with the name "t_next" exist in the kallsyms, which makes > the attach target ambiguous, and the attach should fail. > > Introduce the function bpf_lookup_attach_addr() to do the address lookup, > which will return -EADDRNOTAVAIL when the symbol is not unique. > > We can do the testing with following shell: > > for s in $(cat /proc/kallsyms | awk '{print $3}' | sort | uniq -d) > do > if grep -q "^$s\$" /sys/kernel/debug/tracing/available_filter_functions > then > bpftrace -e "fentry:$s {printf(\"1\");}" -v > fi > done > > The script will find all the duplicated symbols in /proc/kallsyms, which > is also in /sys/kernel/debug/tracing/available_filter_functions, and > attach them with bpftrace. > > After this patch, all the attaching fail with the error: > > The address of function xxx cannot be found > or > No BTF found for xxx > > Signed-off-by: Menglong Dong Maybe we should prevent vmlinux BTF generation for such symbols which are static and have more than one instances? This can be done in pahole and downstream libbpf/kernel do not need to do anything. This can avoid libbpf/kernel runtime overhead since bpf_lookup_attach_addr() could be expensive as it needs to go through ALL symbols, even for unique symbols. > --- > v3: > - reject all the duplicated symbols > v2: > - Lookup both vmlinux and modules symbols when mod is NULL, just like > kallsyms_lookup_name(). > > If the btf is not a modules, shouldn't we lookup on the vmlinux only? > I'm not sure if we should keep the same logic with > kallsyms_lookup_name(). > > - Return the kernel symbol that don't have ftrace location if the symbols > with ftrace location are not available > --- > kernel/bpf/verifier.c | 71 ++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 66 insertions(+), 5 deletions(-) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 53007182b46b..bf4951154605 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -23476,6 +23476,67 @@ static int check_non_sleepable_error_inject(u32 btf_id) > return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id); > } > > +struct symbol_lookup_ctx { > + const char *name; > + unsigned long addr; > +}; > + > +static int symbol_callback(void *data, unsigned long addr) > +{ > + struct symbol_lookup_ctx *ctx = data; > + > + if (ctx->addr) > + return -EADDRNOTAVAIL; > + ctx->addr = addr; > + > + return 0; > +} > + > +static int symbol_mod_callback(void *data, const char *name, unsigned long addr) > +{ > + if (strcmp(((struct symbol_lookup_ctx *)data)->name, name) != 0) > + return 0; > + > + return symbol_callback(data, addr); > +} > + > +/** > + * bpf_lookup_attach_addr: Lookup address for a symbol > + * > + * @mod: kernel module to lookup the symbol, NULL means to lookup both vmlinux > + * and modules symbols > + * @sym: the symbol to resolve > + * @addr: pointer to store the result > + * > + * Lookup the address of the symbol @sym. If multiple symbols with the name > + * @sym exist, -EADDRNOTAVAIL will be returned. > + * > + * Returns: 0 on success, -errno otherwise. > + */ > +static int bpf_lookup_attach_addr(const struct module *mod, const char *sym, > + unsigned long *addr) > +{ > + struct symbol_lookup_ctx ctx = { .addr = 0, .name = sym }; > + const char *mod_name = NULL; > + int err = 0; > + > +#ifdef CONFIG_MODULES > + mod_name = mod ? mod->name : NULL; > +#endif > + if (!mod_name) > + err = kallsyms_on_each_match_symbol(symbol_callback, sym, &ctx); > + > + if (!err && !ctx.addr) > + err = module_kallsyms_on_each_symbol(mod_name, symbol_mod_callback, > + &ctx); > + > + if (!ctx.addr) > + err = -ENOENT; > + *addr = err ? 0 : ctx.addr; > + > + return err; > +} > + > int bpf_check_attach_target(struct bpf_verifier_log *log, > const struct bpf_prog *prog, > const struct bpf_prog *tgt_prog, > @@ -23729,18 +23790,18 @@ int bpf_check_attach_target(struct bpf_verifier_log *log, > if (btf_is_module(btf)) { > mod = btf_try_get_module(btf); > if (mod) > - addr = find_kallsyms_symbol_value(mod, tname); > + ret = bpf_lookup_attach_addr(mod, tname, &addr); > else > - addr = 0; > + ret = -ENOENT; > } else { > - addr = kallsyms_lookup_name(tname); > + ret = bpf_lookup_attach_addr(NULL, tname, &addr); > } > - if (!addr) { > + if (ret) { > module_put(mod); > bpf_log(log, > "The address of function %s cannot be found\n", > tname); > - return -ENOENT; > + return ret; > } > } >