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 9589ECCA48A for ; Fri, 22 Jul 2022 08:44:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229538AbiGVIoR (ORCPT ); Fri, 22 Jul 2022 04:44:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40506 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234425AbiGVIoN (ORCPT ); Fri, 22 Jul 2022 04:44:13 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C6EB39E2BD for ; Fri, 22 Jul 2022 01:44:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1658479450; 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: in-reply-to:in-reply-to:references:references; bh=KPJ7NU0SBJ5IGQBa0MGzAB99cv4bRZOacuI2wl8M0yY=; b=KRgGNmSzQmQGI3a83aPQvg+Yz1K6InJTKZIz3tyqBJ1PS4OaqYSApblbCN9rDbU4uO+SZx x49fG06sXS3OGVlawsYQvI/CoSKih6lAvgh2MWJbXcp5TCGPP8VoehB/GoW7lrTuO2iSWe CmvpxTZN0T/IxzvxEVyEsqbGiXF5Nvs= Received: from mail-pj1-f71.google.com (mail-pj1-f71.google.com [209.85.216.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-583-FEC5LdaFM0aICfMZDXxQQw-1; Fri, 22 Jul 2022 04:44:09 -0400 X-MC-Unique: FEC5LdaFM0aICfMZDXxQQw-1 Received: by mail-pj1-f71.google.com with SMTP id d21-20020a17090ae29500b001f2042edb63so2046711pjz.8 for ; Fri, 22 Jul 2022 01:44:09 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=KPJ7NU0SBJ5IGQBa0MGzAB99cv4bRZOacuI2wl8M0yY=; b=XiwXbe5eC0ZVhyCiFskSHJQ9PU+BOxwhKLr2Cd5eLZJBH2Tagwgy7JnL1c6yASfHuK 0pb479ZwZUhCIdWJ4HSz55G5YT7wAaWE0eJMMKEP/VtJ7A3St1lhhroVBYwSEnbEUEwR Y0o55pE0RGLStNb3IG9BP1Y4k444zSEkixaS127LAFnpx0LFu+Ok2iXFvYAbheJYfba4 gkAPaIDvCHqaewYytojNOAcPTmayCzBD1XuNk9aDPRUJgvEaqKHS8HGF4cJBXD5fQySO 69jjYivanx6TkzQCsz3Meg9Hs6rTOz3z9+3eGkqpaBYX0HxyltVjmTtWh2oxOIv7gjgY MsDA== X-Gm-Message-State: AJIora8G/To9OgK5mgrUtDiLfmPJF0aM0U4kajKHNiYAMr6dgzWudcYJ G/TEfhS88QWo+Dv9WnTvNrEJX+C7MElJpIi54dtr4axCSLNJWzRbRb5VmE6qRC2sWa5P3zS9YzV WubJ6TuLkxE7xsWKqsOQ7ll2Fdq8WEKwH X-Received: by 2002:a17:90b:4a08:b0:1ef:f36b:18e1 with SMTP id kk8-20020a17090b4a0800b001eff36b18e1mr16127725pjb.246.1658479448524; Fri, 22 Jul 2022 01:44:08 -0700 (PDT) X-Google-Smtp-Source: AGRyM1vucvEYBhga7xRfvmO+fpAe+UxKmxIBDDjvW8ENwrZs/TTzp86GPuJSg32bCOVL9jphN7Wm13VUw34PY+/PHI4= X-Received: by 2002:a17:90b:4a08:b0:1ef:f36b:18e1 with SMTP id kk8-20020a17090b4a0800b001eff36b18e1mr16127693pjb.246.1658479448127; Fri, 22 Jul 2022 01:44:08 -0700 (PDT) MIME-Version: 1.0 References: <20220721153625.1282007-1-benjamin.tissoires@redhat.com> <20220721153625.1282007-3-benjamin.tissoires@redhat.com> In-Reply-To: From: Benjamin Tissoires Date: Fri, 22 Jul 2022 10:43:57 +0200 Message-ID: Subject: Re: [PATCH bpf-next v7 02/24] bpf/verifier: allow kfunc to read user provided context To: Kumar Kartikeya Dwivedi Cc: Greg KH , Jiri Kosina , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Shuah Khan , Dave Marchevsky , Joe Stringer , Jonathan Corbet , Tero Kristo , lkml , "open list:HID CORE LAYER" , Networking , bpf , "open list:KERNEL SELFTEST FRAMEWORK" , Linux Doc Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Jul 21, 2022 at 10:15 PM Kumar Kartikeya Dwivedi wrote: > > On Thu, 21 Jul 2022 at 17:36, Benjamin Tissoires > wrote: > > > > When a kfunc was trying to access data from context in a syscall eBPF > > program, the verifier was rejecting the call. > > This is because the syscall context is not known at compile time, and > > so we need to check this when actually accessing it. > > > > Check for the valid memory access and allow such situation to happen. > > > > Signed-off-by: Benjamin Tissoires > > > > --- > > > > LGTM, with just a couple more nits. > Acked-by: Kumar Kartikeya Dwivedi Thanks a lot for the quick review. Sending the new version of just this patch now. Cheers, Benjamin > > > changes in v7: > > - renamed access_t into atype > > - allow zero-byte read > > - check_mem_access() to the correct offset/size > > > > new in v6 > > --- > > kernel/bpf/verifier.c | 21 +++++++++++++++++++++ > > 1 file changed, 21 insertions(+) > > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index 7c1e056624f9..d5fe7e618c52 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -248,6 +248,7 @@ struct bpf_call_arg_meta { > > struct bpf_map *map_ptr; > > bool raw_mode; > > bool pkt_access; > > + bool is_kfunc; > > u8 release_regno; > > int regno; > > int access_size; > > @@ -5170,6 +5171,7 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno, > > struct bpf_call_arg_meta *meta) > > { > > struct bpf_reg_state *regs = cur_regs(env), *reg = ®s[regno]; > > + enum bpf_prog_type prog_type = resolve_prog_type(env->prog); > > u32 *max_access; > > > > switch (base_type(reg->type)) { > > @@ -5223,6 +5225,24 @@ static int check_helper_mem_access(struct bpf_verifier_env *env, int regno, > > env, > > regno, reg->off, access_size, > > zero_size_allowed, ACCESS_HELPER, meta); > > + case PTR_TO_CTX: > > + /* in case of a kfunc called in a program of type SYSCALL, the context is > > + * user supplied, so not computed statically. > > + * Dynamically check it now > > + */ > > + if (prog_type == BPF_PROG_TYPE_SYSCALL && meta && meta->is_kfunc) { > > + enum bpf_access_type atype = meta->raw_mode ? BPF_WRITE : BPF_READ; > > + int offset = access_size - 1; > > + > > + /* Allow zero-byte read from NULL or PTR_TO_CTX */ > > This will not be handling the case for NULL, only for kfunc(ptr_to_ctx, 0) > A null pointer has its reg->type as scalar, so it will be handled by > the default case. > > > + if (access_size == 0) > > + return zero_size_allowed ? 0 : -EINVAL; > > We should use -EACCES, just to be consistent. > > > + > > + return check_mem_access(env, env->insn_idx, regno, offset, BPF_B, > > + atype, -1, false); > > + } > > + > > + fallthrough; > > default: /* scalar_value or invalid ptr */ > > /* Allow zero-byte read from NULL, regardless of pointer type */ > > if (zero_size_allowed && access_size == 0 && > > @@ -5335,6 +5355,7 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state > > WARN_ON_ONCE(regno < BPF_REG_2 || regno > BPF_REG_5); > > > > memset(&meta, 0, sizeof(meta)); > > + meta.is_kfunc = true; > > > > if (may_be_null) { > > saved_reg = *mem_reg; > > -- > > 2.36.1 > > >