From patchwork Wed Jan 25 14:38:10 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Vernet X-Patchwork-Id: 13115755 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 9C586C54E94 for ; Wed, 25 Jan 2023 14:40:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235829AbjAYOkL (ORCPT ); Wed, 25 Jan 2023 09:40:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43280 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235814AbjAYOkJ (ORCPT ); Wed, 25 Jan 2023 09:40:09 -0500 Received: from mail-qv1-f41.google.com (mail-qv1-f41.google.com [209.85.219.41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DDC9014E89; Wed, 25 Jan 2023 06:39:38 -0800 (PST) Received: by mail-qv1-f41.google.com with SMTP id k12so14211799qvj.5; Wed, 25 Jan 2023 06:39:38 -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=9V/N30yEutPTDBJE0EV1CzSj9vieGH2fZk1ThPLan28=; b=IU38gWK1nz3OK42svsvebf68Ij3Sl943AEGDj0omm4IZnnzJbYG2Q+TWuJTzphwjs8 r3SXOuEQy8UfUKtz3oMhRpiS6liyNxjSnSFtaGUF3qyivCiB4FXy7vAuYmzsfVGxtMaL kqrc87v3WTRjY/jlfgFvbd1VaQj8qQimqVUGyRB7O/TA869jPWhsWDcJC/OTPPxMv7mK oSranPyvQM0lXlCtJda0Yhd9tIzEp4BDcLs3dm2HfUyii9bnQ/5Hp/C7ObIEUzMsGQ22 Vv3Zhtx3mgsN+kW2jrm08tYNU3jCb6CO2HRlhkTj6wHdJRg9dbYhiM+604EYHn/utLtn 0VpQ== X-Gm-Message-State: AFqh2kp3aAOw3VpjyUI0h0q3wTW+GQwO2QX8bTMBwxffaE/9IUrzfXy4 rA2vjgWYadoHwl5yKHBMROL6qA3c2tan/YL1 X-Google-Smtp-Source: AMrXdXtBU1RumqY5OgtHrnXwGx8PY0ST/fF2ErsBRPsavDfnyB3vquHeL8iOl/kw3rdF2+Mk2VkPrQ== X-Received: by 2002:a05:6214:3291:b0:534:6aff:e5ca with SMTP id mu17-20020a056214329100b005346affe5camr45172327qvb.1.1674657500161; Wed, 25 Jan 2023 06:38:20 -0800 (PST) Received: from localhost ([24.1.27.177]) by smtp.gmail.com with ESMTPSA id b64-20020a378043000000b00704a9942708sm3579027qkd.73.2023.01.25.06.38.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Jan 2023 06:38:19 -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 v3 1/7] bpf: Disallow NULLable pointers for trusted kfuncs Date: Wed, 25 Jan 2023 08:38:10 -0600 Message-Id: <20230125143816.721952-2-void@manifault.com> X-Mailer: git-send-email 2.39.0 In-Reply-To: <20230125143816.721952-1-void@manifault.com> References: <20230125143816.721952-1-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 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/progs/task_kfunc_failure.c | 4 ++-- 3 files changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 66ec577fcb8b..bb38b01b738f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9194,6 +9194,12 @@ 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/progs/task_kfunc_failure.c b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c index e6950d6a9cf0..f19d54eda4f1 100644 --- a/tools/testing/selftests/bpf/progs/task_kfunc_failure.c +++ b/tools/testing/selftests/bpf/progs/task_kfunc_failure.c @@ -28,7 +28,7 @@ static struct __tasks_kfunc_map_value *insert_lookup_task(struct task_struct *ta } SEC("tp_btf/task_newtask") -__failure __msg("R1 must be referenced or trusted") +__failure __msg("Possibly NULL pointer passed to trusted arg0") int BPF_PROG(task_kfunc_acquire_untrusted, struct task_struct *task, u64 clone_flags) { struct task_struct *acquired; @@ -86,7 +86,7 @@ int BPF_PROG(task_kfunc_acquire_trusted_walked, struct task_struct *task, u64 cl SEC("tp_btf/task_newtask") -__failure __msg("arg#0 pointer type STRUCT task_struct must point") +__failure __msg("Possibly NULL pointer passed to trusted arg0") int BPF_PROG(task_kfunc_acquire_null, struct task_struct *task, u64 clone_flags) { struct task_struct *acquired;