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 X-Spam-Level: X-Spam-Status: No, score=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16D03C433B4 for ; Tue, 13 Apr 2021 23:16:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB71360238 for ; Tue, 13 Apr 2021 23:16:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347915AbhDMXRR (ORCPT ); Tue, 13 Apr 2021 19:17:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231201AbhDMXRP (ORCPT ); Tue, 13 Apr 2021 19:17:15 -0400 Received: from mail-yb1-xb30.google.com (mail-yb1-xb30.google.com [IPv6:2607:f8b0:4864:20::b30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2D998C061574; Tue, 13 Apr 2021 16:16:55 -0700 (PDT) Received: by mail-yb1-xb30.google.com with SMTP id 65so20033563ybc.4; Tue, 13 Apr 2021 16:16:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=QgfRJoCybq9KsaEJIAzOX252QGmZc9D7nckNGd8wwqk=; b=lsqgwiDY2hueWfpFoHPjNpqKf63Yrg8mX8D8SLHoJHZKmel0b1P07wSdUF6J10QhEQ HrtsLKcKzQ1uBtTqsawQBIievd/Gge40kUWDjV3EybgbKtcY+MbAJfXFFlYy+s9UUvdf uSCVbBLhEXv3z/EkNs2UIHz8bDwo97PcIvgccgecRKI/IfWRGuMJtMmS7u0MqS5b0RiF +utIE7K7TLY4wrD8XKDwrY1X31s2X5W8JLJrSSIDvtS8iAurWmyEUL0iG4KuRC8bVGGW 06cgme0b0pazI+4lrFTuVAtZ7WpSogF3+QWU+aUCDKfUCjoqk15+rBbiiMIYu56oDHGW ySuw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=QgfRJoCybq9KsaEJIAzOX252QGmZc9D7nckNGd8wwqk=; b=SwhtNvLdj5ncGQ6X5gbwkFHTmnehAYdEW7IsXlapoNi95w94nAyXP1i62KzJdxD7AD Kqbqf5u2yQ9u6DKZNpETOsQRzq1jbnW7M46DmxIz1liShV7fOvX6RUFpHmC4Af2fH/Mv qWcfyhXh+rDWytc1fhaSAlYf1dCNB46Y54Ooxb7Wg9x20wVa4eJ/veUoKCrguWw8e7+k WU54zv4oxCuVeevSXbedJ+f1Gk5x6YUZw37mRw3ds+O3hEo6lRyULLgM7ZKrs+JMdDvK kpTddDKwH4V76LkjlagRN3uyy7KrTlZ3hWNTuvTAU5gbsyKSsLBfoX2MAfSNEw8rDtF9 qWVA== X-Gm-Message-State: AOAM531dPQ8ztTm0fyaQWQwRYJkDxYscN0TqQdDrVyaSI5AQY0QmqmqH IgKUU/VKNjrIj9/XdhjakNITQhmJSbkPqT8D0w6/fQiq X-Google-Smtp-Source: ABdhPJzVwe6XeypoL5AGx18j/fFFjg2J4NBzEF9zUVH7EBEvCdmGOBfgpttxDsWM1kVweQgS3tr7HNOjUsEmxxs2OqU= X-Received: by 2002:a25:850c:: with SMTP id w12mr4566130ybk.347.1618355814520; Tue, 13 Apr 2021 16:16:54 -0700 (PDT) MIME-Version: 1.0 References: <20210412153754.235500-1-revest@chromium.org> <20210412153754.235500-4-revest@chromium.org> In-Reply-To: <20210412153754.235500-4-revest@chromium.org> From: Andrii Nakryiko Date: Tue, 13 Apr 2021 16:16:43 -0700 Message-ID: Subject: Re: [PATCH bpf-next v3 3/6] bpf: Add a bpf_snprintf helper To: Florent Revest Cc: bpf , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Yonghong Song , KP Singh , Brendan Jackman , open list Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 12, 2021 at 8:38 AM Florent Revest wrote: > > The implementation takes inspiration from the existing bpf_trace_printk > helper but there are a few differences: > > To allow for a large number of format-specifiers, parameters are > provided in an array, like in bpf_seq_printf. > > Because the output string takes two arguments and the array of > parameters also takes two arguments, the format string needs to fit in > one argument. Thankfully, ARG_PTR_TO_CONST_STR is guaranteed to point to > a zero-terminated read-only map so we don't need a format string length > arg. > > Because the format-string is known at verification time, we also do > a first pass of format string validation in the verifier logic. This > makes debugging easier. > > Signed-off-by: Florent Revest > --- > include/linux/bpf.h | 6 ++++ > include/uapi/linux/bpf.h | 28 +++++++++++++++++++ > kernel/bpf/helpers.c | 2 ++ > kernel/bpf/verifier.c | 41 ++++++++++++++++++++++++++++ > kernel/trace/bpf_trace.c | 50 ++++++++++++++++++++++++++++++++++ > tools/include/uapi/linux/bpf.h | 28 +++++++++++++++++++ > 6 files changed, 155 insertions(+) > [...] > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 5f46dd6f3383..d4020e5f91ee 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -5918,6 +5918,41 @@ static int check_reference_leak(struct bpf_verifier_env *env) > return state->acquired_refs ? -EINVAL : 0; > } > > +static int check_bpf_snprintf_call(struct bpf_verifier_env *env, > + struct bpf_reg_state *regs) > +{ > + struct bpf_reg_state *fmt_reg = ®s[BPF_REG_3]; > + struct bpf_reg_state *data_len_reg = ®s[BPF_REG_5]; > + struct bpf_map *fmt_map = fmt_reg->map_ptr; > + int err, fmt_map_off, num_args; > + u64 fmt_addr; > + char *fmt; > + > + /* data must be an array of u64 */ > + if (data_len_reg->var_off.value % 8) > + return -EINVAL; > + num_args = data_len_reg->var_off.value / 8; > + > + /* fmt being ARG_PTR_TO_CONST_STR guarantees that var_off is const > + * and map_direct_value_addr is set. > + */ > + fmt_map_off = fmt_reg->off + fmt_reg->var_off.value; > + err = fmt_map->ops->map_direct_value_addr(fmt_map, &fmt_addr, > + fmt_map_off); > + if (err) > + return err; > + fmt = (char *)fmt_addr + fmt_map_off; > + bot complained about lack of (long) cast before fmt_addr, please address [...] > + /* Maximumly we can have MAX_SNPRINTF_VARARGS parameters, just give > + * all of them to snprintf(). > + */ > + err = snprintf(str, str_size, fmt, BPF_CAST_FMT_ARG(0, args, mod), > + BPF_CAST_FMT_ARG(1, args, mod), BPF_CAST_FMT_ARG(2, args, mod), > + BPF_CAST_FMT_ARG(3, args, mod), BPF_CAST_FMT_ARG(4, args, mod), > + BPF_CAST_FMT_ARG(5, args, mod), BPF_CAST_FMT_ARG(6, args, mod), > + BPF_CAST_FMT_ARG(7, args, mod), BPF_CAST_FMT_ARG(8, args, mod), > + BPF_CAST_FMT_ARG(9, args, mod), BPF_CAST_FMT_ARG(10, args, mod), > + BPF_CAST_FMT_ARG(11, args, mod)); > + > + put_fmt_tmp_buf(); reading this for at least 3rd time, this put_fmt_tmp_buf() looks a bit out of place and kind of random. I think bpf_printf_cleanup() name pairs with bpf_printf_prepare() better. > + > + return err + 1; snprintf() already returns string length *including* terminating zero, so this is wrong > +} > + [...]