From patchwork Fri Jan 20 19:25:17 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Vernet X-Patchwork-Id: 13110432 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 A92D5C05027 for ; Fri, 20 Jan 2023 19:25:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230301AbjATTZj (ORCPT ); Fri, 20 Jan 2023 14:25:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57446 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230197AbjATTZf (ORCPT ); Fri, 20 Jan 2023 14:25:35 -0500 Received: from mail-qv1-f45.google.com (mail-qv1-f45.google.com [209.85.219.45]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 099F2CB50A; Fri, 20 Jan 2023 11:25:30 -0800 (PST) Received: by mail-qv1-f45.google.com with SMTP id t7so4453571qvv.3; Fri, 20 Jan 2023 11:25:29 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=KJ/CIF8V3Oz85fXn1ATcxkeRERKTOn9zuVe6bz+JYpA=; b=wQT3eh4Mo7zXBcxmWSL6uJRsj/5QGoGRpazZxOn4PsDBd8csQGHW2EDOrB7keJapf+ 4pgw59WLie/iyuc8QZZtrXsn7pDgw/fthGNpmExKbZ9Ar1H69N6BC7xyP9KtvYKiyZYA IxfvvxtpSLrbnowCO7qzrkR3vN/Fr6IJg+tE/vIJAKOF3TemusbmPmnkZyS7c1Zoe5ua 8jyse6PIVd9FGLKRSpJQuT4sbaS5tFErfV4hcW/KMFtfr/K3O5Brh8ZDD//orJCks2P+ Ws13mjWLgWkEClJxwpVt53AVnRPdMsW+rC5os4e18/SCkXbfgDlM5oTVPKWME2zVSB4q P1Ig== X-Gm-Message-State: AFqh2kqXpsGekQ4K8A660DqfpwL1cjy/esy/JAowIk+wyt0hOxtYS7TT buwkS+jbPjaCBaMtYa63TK+ME6APBTHACwbm X-Google-Smtp-Source: AMrXdXs14Di1mE3nUh3fZe+Fynxkq/nd7+2wjQZJSVsF6Czh5ka4fvGce7GL/2nXK3TVWW7uqU9QeQ== X-Received: by 2002:ad4:584b:0:b0:531:8b4b:b59d with SMTP id de11-20020ad4584b000000b005318b4bb59dmr51044840qvb.50.1674242728609; Fri, 20 Jan 2023 11:25:28 -0800 (PST) Received: from localhost ([2620:10d:c091:480::1:2fc9]) by smtp.gmail.com with ESMTPSA id br38-20020a05620a462600b00706b09b16fasm6085348qkb.11.2023.01.20.11.25.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Jan 2023 11:25:28 -0800 (PST) From: David Vernet To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@meta.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, tj@kernel.org, memxor@gmail.com Subject: [PATCH bpf-next v2 3/9] bpf: Disallow NULLable pointers for trusted kfuncs Date: Fri, 20 Jan 2023 13:25:17 -0600 Message-Id: <20230120192523.3650503-4-void@manifault.com> X-Mailer: git-send-email 2.39.0 In-Reply-To: <20230120192523.3650503-1-void@manifault.com> References: <20230120192523.3650503-1-void@manifault.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net KF_TRUSTED_ARGS kfuncs currently have a subtle and insidious bug in validating pointers to scalars. Say that you have a kfunc like the following, which takes an array as the first argument: bool bpf_cpumask_empty(const struct cpumask *cpumask) { return cpumask_empty(cpumask); } ... BTF_ID_FLAGS(func, bpf_cpumask_empty, KF_TRUSTED_ARGS) ... If a BPF program were to invoke the kfunc with a NULL argument, it would crash the kernel. The reason is that struct cpumask is defined as a bitmap, which is itself defined as an array, and is accessed as a memory address memory by bitmap operations. So when the verifier analyzes the register, it interprets it as a pointer to a scalar struct, which is an array of size 8. check_mem_reg() then sees that the register is NULL, and returns 0, and the kfunc crashes when it passes it down to the cpumask wrappers. To fix this, this patch adds a check for KF_ARG_PTR_TO_MEM which verifies that the register doesn't contain a possibly-NULL pointer if the kfunc is KF_TRUSTED_ARGS. Signed-off-by: David Vernet --- kernel/bpf/verifier.c | 6 ++++++ tools/testing/selftests/bpf/prog_tests/cgrp_kfunc.c | 4 ++-- tools/testing/selftests/bpf/prog_tests/task_kfunc.c | 4 ++-- 3 files changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ca5d601fb3cf..a466887f5334 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -8937,6 +8937,12 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ return -EINVAL; } + if (is_kfunc_trusted_args(meta) && + (register_is_null(reg) || type_may_be_null(reg->type))) { + verbose(env, "Possibly NULL pointer passed to trusted arg%d\n", i); + return -EACCES; + } + if (reg->ref_obj_id) { if (is_kfunc_release(meta) && meta->ref_obj_id) { verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n", diff --git a/tools/testing/selftests/bpf/prog_tests/cgrp_kfunc.c b/tools/testing/selftests/bpf/prog_tests/cgrp_kfunc.c index 973f0c5af965..f3bb0e16e088 100644 --- a/tools/testing/selftests/bpf/prog_tests/cgrp_kfunc.c +++ b/tools/testing/selftests/bpf/prog_tests/cgrp_kfunc.c @@ -93,11 +93,11 @@ static struct { const char *prog_name; const char *expected_err_msg; } failure_tests[] = { - {"cgrp_kfunc_acquire_untrusted", "R1 must be referenced or trusted"}, + {"cgrp_kfunc_acquire_untrusted", "Possibly NULL pointer passed to trusted arg0"}, {"cgrp_kfunc_acquire_fp", "arg#0 pointer type STRUCT cgroup must point"}, {"cgrp_kfunc_acquire_unsafe_kretprobe", "reg type unsupported for arg#0 function"}, {"cgrp_kfunc_acquire_trusted_walked", "R1 must be referenced or trusted"}, - {"cgrp_kfunc_acquire_null", "arg#0 pointer type STRUCT cgroup must point"}, + {"cgrp_kfunc_acquire_null", "Possibly NULL pointer passed to trusted arg0"}, {"cgrp_kfunc_acquire_unreleased", "Unreleased reference"}, {"cgrp_kfunc_get_non_kptr_param", "arg#0 expected pointer to map value"}, {"cgrp_kfunc_get_non_kptr_acquired", "arg#0 expected pointer to map value"}, diff --git a/tools/testing/selftests/bpf/prog_tests/task_kfunc.c b/tools/testing/selftests/bpf/prog_tests/task_kfunc.c index 18848c31e36f..a4f49e8dc7e8 100644 --- a/tools/testing/selftests/bpf/prog_tests/task_kfunc.c +++ b/tools/testing/selftests/bpf/prog_tests/task_kfunc.c @@ -87,11 +87,11 @@ static struct { const char *prog_name; const char *expected_err_msg; } failure_tests[] = { - {"task_kfunc_acquire_untrusted", "R1 must be referenced or trusted"}, + {"task_kfunc_acquire_untrusted", "Possibly NULL pointer passed to trusted arg0"}, {"task_kfunc_acquire_fp", "arg#0 pointer type STRUCT task_struct must point"}, {"task_kfunc_acquire_unsafe_kretprobe", "reg type unsupported for arg#0 function"}, {"task_kfunc_acquire_trusted_walked", "R1 must be referenced or trusted"}, - {"task_kfunc_acquire_null", "arg#0 pointer type STRUCT task_struct must point"}, + {"task_kfunc_acquire_null", "Possibly NULL pointer passed to trusted arg0"}, {"task_kfunc_acquire_unreleased", "Unreleased reference"}, {"task_kfunc_get_non_kptr_param", "arg#0 expected pointer to map value"}, {"task_kfunc_get_non_kptr_acquired", "arg#0 expected pointer to map value"},