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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 59080C433FE for ; Wed, 13 Oct 2021 19:56:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 41F60611CE for ; Wed, 13 Oct 2021 19:56:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238371AbhJMT6P (ORCPT ); Wed, 13 Oct 2021 15:58:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41786 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236791AbhJMT6O (ORCPT ); Wed, 13 Oct 2021 15:58:14 -0400 Received: from mail-lf1-x12d.google.com (mail-lf1-x12d.google.com [IPv6:2a00:1450:4864:20::12d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1BB2FC061746 for ; Wed, 13 Oct 2021 12:56:11 -0700 (PDT) Received: by mail-lf1-x12d.google.com with SMTP id y15so16802971lfk.7 for ; Wed, 13 Oct 2021 12:56:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloudflare.com; s=google; h=references:user-agent:from:to:cc:subject:in-reply-to:date :message-id:mime-version; bh=qKH85f/X/bTM1HBd2jb8yR7hV1r7tXpdbyJxEIUbYFg=; b=IrFtpUHHjhCjoRTsTIuTweLrfzJObNtGoSCXCsaLWFNHKsTRzgvJ055GYOlkux+FY2 SL4/Ct2NU4cOXVX5KzbrkO6L4NU3buaYTu0n+RExjMKoh6AkQGFyikPxpPpxolnvDRZv /aLUPlSU3vyjEA+TSWAzjLCAYqNpOPqtkCQgg= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:references:user-agent:from:to:cc:subject :in-reply-to:date:message-id:mime-version; bh=qKH85f/X/bTM1HBd2jb8yR7hV1r7tXpdbyJxEIUbYFg=; b=2OBCBcNsk4MQnHF6rbQLvCT+sLsjXLcyQ792DzSjW8+NhuOAAOznDHDmyN6ADNV9HY SmWjP9GALacyi6r9YueaiV+dbyvcrvKLor9G5QHtL1nlld6CWzlExgV4UigPuVYJbj9P Cw104764g24dWDgYEhblMe/rnKmsIrKgDPD2Exf5ez8di/e1F1AHI3Jy1ZaeyAszuxhG WjQ7uCpUEw5VStLuqU9N9lnbJ5KIAB1aWQbFxZ5K+aM5dEPtQWJhttzQTfTcBIn/MwQ0 3bwn247lxNYy9TRYvCJH8RUmkXwdVIO8NThk0haFsrlgYcwqe3uij97PHXONNkOcg2Rz eO5A== X-Gm-Message-State: AOAM531Ug5mHyDZR1hcPklUpQOT4daBlC5riQ3niqH+k/NTteBGf1OuC POSYxIX3+yq1Z8dxw/E7rP3xCA== X-Google-Smtp-Source: ABdhPJwHphrDVmMbMJ7FNjq5CHkLWjARm6t6dQ3Imk/b5ETfBXq/2tEXlahAHUelGKMPUbS6bJZYhQ== X-Received: by 2002:a05:6512:4029:: with SMTP id br41mr961117lfb.233.1634154969452; Wed, 13 Oct 2021 12:56:09 -0700 (PDT) Received: from cloudflare.com ([2a01:110f:480d:6f00:ff34:bf12:ef2:5071]) by smtp.gmail.com with ESMTPSA id d19sm47867ljl.87.2021.10.13.12.56.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Oct 2021 12:56:09 -0700 (PDT) References: <20211012135935.37054-1-lmb@cloudflare.com> User-agent: mu4e 1.1.0; emacs 27.2 From: Jakub Sitnicki To: Lorenz Bauer Cc: nicolas.dichtel@6wind.com, luke.r.nels@gmail.com, Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , kernel-team@cloudflare.com, linux-riscv@lists.infradead.org, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH v2 0/4] Fix up bpf_jit_limit some more In-reply-to: <20211012135935.37054-1-lmb@cloudflare.com> Date: Wed, 13 Oct 2021 21:56:08 +0200 Message-ID: <87wnmgg0mf.fsf@cloudflare.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Oct 12, 2021 at 03:59 PM CEST, Lorenz Bauer wrote: > Some more cleanups around bpf_jit_limit to make it readable via sysctl. > > Jakub raised the point that a sysctl toggle is UAPI and therefore > can't be easily changed later on. I tried to find another place to stick > the info, but couldn't find a good one. All the current BPF knobs are in > sysctl. > > There are examples of read only sysctls: > $ sudo find /proc/sys -perm 0444 | wc -l > 90 > > There are no examples of sysctls with mode 0400 however: > $ sudo find /proc/sys -perm 0400 | wc -l > 0 > > Thoughts? I threw this idea out there during LPC already, that it would be cool to use BPF iterators for that. Pinned/preloaded iterators were made for dumping kernel data on demand after all. What is missing is a BPF iterator type that would run the program just once (there is just one thing to print), and a BPF helper to lookup symbol's address. I thought this would require a bit of work, but actually getting a PoC (see below) to work was rather pleasntly straightforward. Perhaps a bit of a hack but I'd consider it as an alternative. -- >8 -- >From bef52bec926ea08ccd32a3421d195210ae7d3b38 Mon Sep 17 00:00:00 2001 From: Jakub Sitnicki Date: Wed, 13 Oct 2021 18:54:12 +0200 Subject: [PATCH] RFC: BPF iterator that always runs the program just once The test iterator loads the value of bpf_jit_current kernel global: # bpftool iter pin tools/testing/selftests/bpf/bpf_iter_once.o /sys/fs/bpf/bpf_jit_current libbpf: elf: skipping unrecognized data section(6) .rodata.str1.1 # cat /sys/fs/bpf/bpf_jit_current 2 # for ((i=0; i<10; i++)); do iptables -A OUTPUT -m bpf --bytecode '1,6 0 0 0' -j ACCEPT; done # cat /sys/fs/bpf/bpf_jit_current 12 # iptables -F OUTPUT # cat /sys/fs/bpf/bpf_jit_current 2 Signed-off-by: Jakub Sitnicki --- include/uapi/linux/bpf.h | 7 ++ kernel/bpf/Makefile | 2 +- kernel/bpf/helpers.c | 22 ++++++ kernel/bpf/once_iter.c | 76 +++++++++++++++++++ tools/include/uapi/linux/bpf.h | 7 ++ .../selftests/bpf/progs/bpf_iter_once.c | 33 ++++++++ 6 files changed, 146 insertions(+), 1 deletion(-) create mode 100644 kernel/bpf/once_iter.c create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_once.c diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 6fc59d61937a..ec117ebd3d58 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -4909,6 +4909,12 @@ union bpf_attr { * Return * The number of bytes written to the buffer, or a negative error * in case of failure. + * + * long bpf_kallsyms_lookup_name(const char *name, u32 name_size) + * Description + * Lookup the address for a symbol. + * Return + * Returns 0 if not found. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -5089,6 +5095,7 @@ union bpf_attr { FN(task_pt_regs), \ FN(get_branch_snapshot), \ FN(trace_vprintk), \ + FN(kallsyms_lookup_name), \ /* */ /* integer value in 'imm' field of BPF_CALL instruction selects which helper diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile index 7f33098ca63f..f2dc86ea0f2d 100644 --- a/kernel/bpf/Makefile +++ b/kernel/bpf/Makefile @@ -6,7 +6,7 @@ cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse endif CFLAGS_core.o += $(call cc-disable-warning, override-init) $(cflags-nogcse-yy) -obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o task_iter.o prog_iter.o +obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o task_iter.o prog_iter.o once_iter.o obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 1ffd469c217f..d2524df54ab5 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -15,6 +15,7 @@ #include #include #include +#include #include "../../lib/kstrtox.h" @@ -1328,6 +1329,25 @@ void bpf_timer_cancel_and_free(void *val) kfree(t); } +BPF_CALL_2(bpf_kallsyms_lookup_name, const char *, name, u32, name_size) +{ + const char *name_end; + + name_end = strnchr(name, name_size, 0); + if (!name_end) + return -EINVAL; + + return kallsyms_lookup_name(name); +} + +static const struct bpf_func_proto bpf_kallsyms_lookup_name_proto = { + .func = bpf_kallsyms_lookup_name, + .gpl_only = true, + .ret_type = RET_INTEGER, + .arg1_type = ARG_PTR_TO_MEM, + .arg2_type = ARG_CONST_SIZE, +}; + const struct bpf_func_proto bpf_get_current_task_proto __weak; const struct bpf_func_proto bpf_get_current_task_btf_proto __weak; const struct bpf_func_proto bpf_probe_read_user_proto __weak; @@ -1404,6 +1424,8 @@ bpf_base_func_proto(enum bpf_func_id func_id) return &bpf_timer_start_proto; case BPF_FUNC_timer_cancel: return &bpf_timer_cancel_proto; + case BPF_FUNC_kallsyms_lookup_name: + return &bpf_kallsyms_lookup_name_proto; default: break; } diff --git a/kernel/bpf/once_iter.c b/kernel/bpf/once_iter.c new file mode 100644 index 000000000000..f2635f1b0043 --- /dev/null +++ b/kernel/bpf/once_iter.c @@ -0,0 +1,76 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Copyright (c) 2021 Cloudflare, Inc. */ + +#include +#include +#include + +static struct {} empty; + +static void *once_seq_start(struct seq_file *seq, loff_t *pos) +{ + if (*pos == 0) + ++*pos; + return ∅ +} + +static void *once_seq_next(struct seq_file *seq, void *v, loff_t *pos) +{ + ++*pos; + return NULL; +} + +struct bpf_iter__once { + __bpf_md_ptr(struct bpf_iter_meta *, meta); +}; + +DEFINE_BPF_ITER_FUNC(once, struct bpf_iter_meta *meta) + +static int once_seq_show(struct seq_file *seq, void *v) +{ + return 0; +} + +static void once_seq_stop(struct seq_file *seq, void *v) +{ + struct bpf_iter_meta meta; + struct bpf_iter__once ctx; + struct bpf_prog *prog; + + meta.seq = seq; + prog = bpf_iter_get_info(&meta, true); + if (!prog) + return; + + meta.seq = seq; + ctx.meta = &meta; + bpf_iter_run_prog(prog, &ctx); +} + +static const struct seq_operations once_seq_ops = { + .start = once_seq_start, + .next = once_seq_next, + .stop = once_seq_stop, + .show = once_seq_show, +}; + +static const struct bpf_iter_seq_info once_seq_info = { + .seq_ops = &once_seq_ops, + .init_seq_private = NULL, + .fini_seq_private = NULL, + .seq_priv_size = 0, +}; + +static struct bpf_iter_reg once_reg_info = { + .target = "once", + .feature = 0, + .ctx_arg_info_size = 0, + .ctx_arg_info = {}, + .seq_info = &once_seq_info, +}; + +static int __init once_iter_init(void) +{ + return bpf_iter_reg_target(&once_reg_info); +} +late_initcall(once_iter_init); diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 6fc59d61937a..ec117ebd3d58 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -4909,6 +4909,12 @@ union bpf_attr { * Return * The number of bytes written to the buffer, or a negative error * in case of failure. + * + * long bpf_kallsyms_lookup_name(const char *name, u32 name_size) + * Description + * Lookup the address for a symbol. + * Return + * Returns 0 if not found. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -5089,6 +5095,7 @@ union bpf_attr { FN(task_pt_regs), \ FN(get_branch_snapshot), \ FN(trace_vprintk), \ + FN(kallsyms_lookup_name), \ /* */ /* integer value in 'imm' field of BPF_CALL instruction selects which helper diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_once.c b/tools/testing/selftests/bpf/progs/bpf_iter_once.c new file mode 100644 index 000000000000..e5e6d779eb51 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/bpf_iter_once.c @@ -0,0 +1,33 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2021 Cloudflare, Inc. */ + +#include "bpf_iter.h" +#include + +char _license[] SEC("license") = "GPL"; + +SEC("iter/once") +int dump_once(struct bpf_iter__once *ctx) +{ + const char sym_name[] = "bpf_jit_current"; + struct seq_file *seq = ctx->meta->seq; + unsigned long sym_addr; + s64 value = 0; + int err; + + sym_addr = bpf_kallsyms_lookup_name(sym_name, sizeof(sym_name)); + if (!sym_addr) { + BPF_SEQ_PRINTF(seq, "failed to find %s address\n", sym_name); + return 0; + } + + err = bpf_probe_read_kernel(&value, sizeof(value), (void *)sym_addr); + if (err) { + BPF_SEQ_PRINTF(seq, "failed to read from %s address\n", sym_name); + return 0; + } + + BPF_SEQ_PRINTF(seq, "%ld\n", value); + + return 0; +} -- 2.31.1