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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 16958C3F2D1 for ; Wed, 4 Mar 2020 15:48:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA70E22B48 for ; Wed, 4 Mar 2020 15:48:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="jeBpg3zx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729800AbgCDPsU (ORCPT ); Wed, 4 Mar 2020 10:48:20 -0500 Received: from mail-wm1-f66.google.com ([209.85.128.66]:38525 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387801AbgCDPsA (ORCPT ); Wed, 4 Mar 2020 10:48:00 -0500 Received: by mail-wm1-f66.google.com with SMTP id u9so2377329wml.3 for ; Wed, 04 Mar 2020 07:47:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=OnY0sLzc6EG75w+2zGbx52f2fr6wBzB9p2HqJRSWjIE=; b=jeBpg3zx7Fq/WdtomdsFbKI/7lD4yn2XfYDa5pB6rTmiZ12Y115rivK54p00W4iK3w 1oirVnEoTQV9OKlV+/MaN2u15j9SZI2YyEz2rRzfxxDzE3go9t3zRfzpO8zmihWIMJLb 2jSWVAnSZjoyr7Y3W/CZpolMgiS8wq7Ypo414= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=OnY0sLzc6EG75w+2zGbx52f2fr6wBzB9p2HqJRSWjIE=; b=W+ga/UAzH0aOfN0oFL8N70y96IJePog8d3JCIw6PgqxIHq4qS3gsuwcFJfysc3v4Nl SRU/PgiO+p9Ek3zAt/PENWRkV3E/bUcl0h0ImaX/bueIaYwxLwS7UtM0xXUAXA4jrj3x ptw+Xr0eIRant7gbOtq30fV31xIB91PeTuHMOPikDRTQ3epus4sQyr7UQs+cuFpI6lbc 6wE8zlmYy5DKC9YsReTzmIQlq3eY9PBEwufk8ZAYHQVAKK+clPTtFpHkaHfKZYJrl6vm Qpn1eqp+vNWhduRoFJNkPERCvX7M3/rY1G+Qa/Smy5t998hDtSJEpVuUMmnsKNh/T9GJ te3w== X-Gm-Message-State: ANhLgQ1Rn3AtzWRQrCDDQ/aSpd3TpuMIks9sa1pRXFDpj0QSmDDugd47 eF2qfrNdWGTp+Uh0eP7hZHEixw== X-Google-Smtp-Source: ADFU+vtyWWEd7y4ar3XJjKvHHh8Lk8eZl5HKOd3/C8g5c0EZydhJWiwJ4rMhfCmFH57jJGr+drrg5A== X-Received: by 2002:a1c:1b11:: with SMTP id b17mr4150774wmb.93.1583336878995; Wed, 04 Mar 2020 07:47:58 -0800 (PST) Received: from kpsingh-kernel.localdomain ([2a00:79e1:abc:308:8ca0:6f80:af01:b24]) by smtp.gmail.com with ESMTPSA id u25sm4816091wml.17.2020.03.04.07.47.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Mar 2020 07:47:58 -0800 (PST) From: KP Singh To: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Cc: Andrii Nakryiko , Alexei Starovoitov , Daniel Borkmann , Paul Turner , Jann Horn , Florent Revest , Brendan Jackman Subject: [PATCH bpf-next v3 4/7] bpf: Attachment verification for BPF_MODIFY_RETURN Date: Wed, 4 Mar 2020 16:47:44 +0100 Message-Id: <20200304154747.23506-5-kpsingh@chromium.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200304154747.23506-1-kpsingh@chromium.org> References: <20200304154747.23506-1-kpsingh@chromium.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: KP Singh - Allow BPF_MODIFY_RETURN attachment only to functions that are: * Whitelisted for error injection by checking within_error_injection_list. Similar discussions happened for the bpf_override_return helper. * security hooks, this is expected to be cleaned up with the LSM changes after the KRSI patches introduce the LSM_HOOK macro: https://lore.kernel.org/bpf/20200220175250.10795-1-kpsingh@chromium.org/ - The attachment is currently limited to functions that return an int. This can be extended later other types (e.g. PTR). Signed-off-by: KP Singh Acked-by: Andrii Nakryiko --- kernel/bpf/btf.c | 28 ++++++++++++++++++++-------- kernel/bpf/verifier.c | 31 +++++++++++++++++++++++++++++++ 2 files changed, 51 insertions(+), 8 deletions(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 30841fb8b3c0..50080add2ab9 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -3710,14 +3710,26 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, nr_args--; } - if ((prog->expected_attach_type == BPF_TRACE_FEXIT || - prog->expected_attach_type == BPF_MODIFY_RETURN) && - arg == nr_args) { - if (!t) - /* Default prog with 5 args. 6th arg is retval. */ - return true; - /* function return type */ - t = btf_type_by_id(btf, t->type); + if (arg == nr_args) { + if (prog->expected_attach_type == BPF_TRACE_FEXIT) { + if (!t) + return true; + t = btf_type_by_id(btf, t->type); + } else if (prog->expected_attach_type == BPF_MODIFY_RETURN) { + /* For now the BPF_MODIFY_RETURN can only be attached to + * functions that return an int. + */ + if (!t) + return false; + + t = btf_type_skip_modifiers(btf, t->type, NULL); + if (!btf_type_is_int(t)) { + bpf_log(log, + "ret type %s not allowed for fmod_ret\n", + btf_kind_str[BTF_INFO_KIND(t->info)]); + return false; + } + } } else if (arg >= nr_args) { bpf_log(log, "func '%s' doesn't have %d-th argument\n", tname, arg + 1); diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 2460c8e6b5be..ae32517d4ccd 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -19,6 +19,7 @@ #include #include #include +#include #include "disasm.h" @@ -9800,6 +9801,33 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env) return 0; } +#define SECURITY_PREFIX "security_" + +static int check_attach_modify_return(struct bpf_verifier_env *env) +{ + struct bpf_prog *prog = env->prog; + unsigned long addr = (unsigned long) prog->aux->trampoline->func.addr; + + if (within_error_injection_list(addr)) + return 0; + + /* This is expected to be cleaned up in the future with the KRSI effort + * introducing the LSM_HOOK macro for cleaning up lsm_hooks.h. + */ + if (!strncmp(SECURITY_PREFIX, prog->aux->attach_func_name, + sizeof(SECURITY_PREFIX) - 1)) { + + if (!capable(CAP_MAC_ADMIN)) + return -EPERM; + + return 0; + } + + verbose(env, "fmod_ret attach_btf_id %u (%s) is not modifiable\n", + prog->aux->attach_btf_id, prog->aux->attach_func_name); + + return -EINVAL; +} static int check_attach_btf_id(struct bpf_verifier_env *env) { @@ -10000,6 +10028,9 @@ static int check_attach_btf_id(struct bpf_verifier_env *env) } tr->func.addr = (void *)addr; prog->aux->trampoline = tr; + + if (prog->expected_attach_type == BPF_MODIFY_RETURN) + ret = check_attach_modify_return(env); out: mutex_unlock(&tr->mutex); if (ret) -- 2.20.1