From patchwork Fri Sep 2 13:29:18 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Benjamin Tissoires X-Patchwork-Id: 602291 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 6E34AC38145 for ; Fri, 2 Sep 2022 14:09:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236317AbiIBOJj (ORCPT ); Fri, 2 Sep 2022 10:09:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238936AbiIBOIX (ORCPT ); Fri, 2 Sep 2022 10:08:23 -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 ESMTPS id 816614E600 for ; Fri, 2 Sep 2022 06:36:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1662125778; 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=UmXuOjUugSdvFfhnfCLRZhRw10ucC5QWiKjJxW2knIY=; b=McfIhz2vG7DUj3rm3gkkmCvTAd7l6C8iaXkYHy3gEUBIyQyismP77rsT88hbe1t4z/j1Jy +zhR/s6/olMSkxQUGMilbZLOqDWSrIAp/dpxksg9y4lHl6dzsA1Ej6XO7+XKgiW8zg6vjs os0/Zi4Bbrvs3jY4SwXMk+Lj1MW8bqE= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-558-C2v1YD0hOziZ3XJ_0yDWmA-1; Fri, 02 Sep 2022 09:29:56 -0400 X-MC-Unique: C2v1YD0hOziZ3XJ_0yDWmA-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 7B6B63C0F37B; Fri, 2 Sep 2022 13:29:55 +0000 (UTC) Received: from plouf.redhat.com (unknown [10.39.193.218]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1BEDC492C3B; Fri, 2 Sep 2022 13:29:51 +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 v10 03/23] bpf/verifier: allow all functions to read user provided context Date: Fri, 2 Sep 2022 15:29:18 +0200 Message-Id: <20220902132938.2409206-4-benjamin.tissoires@redhat.com> In-Reply-To: <20220902132938.2409206-1-benjamin.tissoires@redhat.com> References: <20220902132938.2409206-1-benjamin.tissoires@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.9 Precedence: bulk List-ID: X-Mailing-List: linux-input@vger.kernel.org When a function was trying to access data from context in a syscall eBPF program, the verifier was rejecting the call unless it was accessing the first element. 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 if there is no convert_ctx callback, and allow such situation to happen. There is a slight hiccup with subprogs. btf_check_subprog_arg_match() will check that the types are matching, which is a good thing, but to have an accurate result, it hides the fact that the context register may be null. This makes env->prog->aux->max_ctx_offset being set to the size of the context, which is incompatible with a NULL context. Solve that last problem by storing max_ctx_offset before the type check and restoring it after. Acked-by: Kumar Kartikeya Dwivedi Signed-off-by: Benjamin Tissoires --- changes in v10: - dropped the hunk in btf.c saving/restoring max_ctx_offset changes in v9: - rewrote the commit title and description - made it so all functions can make use of context even if there is no convert_ctx - remove the is_kfunc field in bpf_call_arg_meta changes in v8: - fixup comment - return -EACCESS instead of -EINVAL for consistency 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 | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d27fae3ce949..3f9e6fa92cde 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5233,6 +5233,25 @@ 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 the function doesn't know how to access the context, + * (because we are in a program of type SYSCALL for example), we + * can not statically check its size. + * Dynamically check it now. + */ + if (!env->ops->convert_ctx_access) { + enum bpf_access_type atype = meta && meta->raw_mode ? BPF_WRITE : BPF_READ; + int offset = access_size - 1; + + /* Allow zero-byte read from PTR_TO_CTX */ + if (access_size == 0) + return zero_size_allowed ? 0 : -EACCES; + + 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 &&