From patchwork Thu Jul 21 15:36:03 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Benjamin Tissoires X-Patchwork-Id: 12925396 X-Patchwork-Delegate: bpf@iogearbox.net 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 85497C433EF for ; Thu, 21 Jul 2022 15:37:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232679AbiGUPhh (ORCPT ); Thu, 21 Jul 2022 11:37:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53120 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232519AbiGUPhE (ORCPT ); Thu, 21 Jul 2022 11:37:04 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E1A8088763 for ; Thu, 21 Jul 2022 08:36:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1658417808; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TfLxNfPKx31yeXS764YWUeQwYwecwzkxNt5EZKfDWDU=; b=h8GqvZdpPFM66ug8UY9QvHn+NhTPRgFYLXuIdQHT3at83XQ3ZHexnn8bM5531Ax1fPzoks D6zynHH3m3wPvXUoeEhL9sQcuZgwo6S3o1OSa95VeXmNf1G7GaVinffVeYRhXhybkrUic+ waTP5HnsKUhDM0IHEQLvftnWPJ+A8uU= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-78-D4udUILGMH6nCS1jvRZAUw-1; Thu, 21 Jul 2022 11:36:39 -0400 X-MC-Unique: D4udUILGMH6nCS1jvRZAUw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 39C37800124; Thu, 21 Jul 2022 15:36:38 +0000 (UTC) Received: from plouf.redhat.com (unknown [10.39.194.200]) by smtp.corp.redhat.com (Postfix) with ESMTP id 17F992166B26; Thu, 21 Jul 2022 15:36:34 +0000 (UTC) From: Benjamin Tissoires To: Greg KH , Jiri Kosina , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , Kumar Kartikeya Dwivedi , John Fastabend , KP Singh , Shuah Khan , Dave Marchevsky , Joe Stringer , Jonathan Corbet Cc: Tero Kristo , linux-kernel@vger.kernel.org, linux-input@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org, Benjamin Tissoires Subject: [PATCH bpf-next v7 02/24] bpf/verifier: allow kfunc to read user provided context Date: Thu, 21 Jul 2022 17:36:03 +0200 Message-Id: <20220721153625.1282007-3-benjamin.tissoires@redhat.com> In-Reply-To: <20220721153625.1282007-1-benjamin.tissoires@redhat.com> References: <20220721153625.1282007-1-benjamin.tissoires@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net 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 Acked-by: Kumar Kartikeya Dwivedi --- 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 */ + if (access_size == 0) + return zero_size_allowed ? 0 : -EINVAL; + + 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;