From patchwork Fri Sep 2 13:29:17 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Benjamin Tissoires X-Patchwork-Id: 602693 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 8229BECAAD5 for ; Fri, 2 Sep 2022 14:05:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238809AbiIBOFa (ORCPT ); Fri, 2 Sep 2022 10:05:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54348 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238881AbiIBOEo (ORCPT ); Fri, 2 Sep 2022 10:04:44 -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 1DB3216D150 for ; Fri, 2 Sep 2022 06:33:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1662125595; 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=nHk5BTlmONqv6fEHgegmNNqBCjtFGaXUYYFXNjhPeHw=; b=GUj1Zqq/PMenlTkrdztcPrTSZOQkgYC2Y6k4FYvhIfbmVdi53fDg7bhMjB+QYA14+C/X96 quwmhRvZz7qlKbzIr9yfeMA58ie0ifsn2eE2ZglsasfltpLQigIigf/wklelD3MVILyPeO DsuhOCvvGyaGCRwuD74k3KoNPcmWaQQ= 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-434-Ac5ZtnOcPti7L1bTbu94bw-1; Fri, 02 Sep 2022 09:29:52 -0400 X-MC-Unique: Ac5ZtnOcPti7L1bTbu94bw-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 CF56485A58F; Fri, 2 Sep 2022 13:29:51 +0000 (UTC) Received: from plouf.redhat.com (unknown [10.39.193.218]) by smtp.corp.redhat.com (Postfix) with ESMTP id 98605492CA2; Fri, 2 Sep 2022 13:29:48 +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 02/23] bpf: split btf_check_subprog_arg_match in two Date: Fri, 2 Sep 2022 15:29:17 +0200 Message-Id: <20220902132938.2409206-3-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 btf_check_subprog_arg_match() was used twice in verifier.c: - when checking for the type mismatches between a (sub)prog declaration and BTF - when checking the call of a subprog to see if the provided arguments are correct and valid This is problematic when we check if the first argument of a program (pointer to ctx) is correctly accessed: To be able to ensure we access a valid memory in the ctx, the verifier assumes the pointer to context is not null. This has the side effect of marking the program accessing the entire context, even if the context is never dereferenced. For example, by checking the context access with the current code, the following eBPF program would fail with -EINVAL if the ctx is set to null from the userspace: ``` SEC("syscall") int prog(struct my_ctx *args) { return 0; } ``` In that particular case, we do not want to actually check that the memory is correct while checking for the BTF validity, but we just want to ensure that the (sub)prog definition matches the BTF we have. So split btf_check_subprog_arg_match() in two so we can actually check for the memory used when in a call, and ignore that part when not. Note that a further patch is in preparation to disentangled btf_check_func_arg_match() from these two purposes, and so right now we just add a new hack around that by adding a boolean to this function. Signed-off-by: Benjamin Tissoires --- new in v10 --- include/linux/bpf.h | 2 ++ kernel/bpf/btf.c | 54 +++++++++++++++++++++++++++++++++++++++---- kernel/bpf/verifier.c | 2 +- 3 files changed, 52 insertions(+), 6 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 9c1674973e03..c9c72a089579 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1943,6 +1943,8 @@ int btf_distill_func_proto(struct bpf_verifier_log *log, struct bpf_reg_state; int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog, struct bpf_reg_state *regs); +int btf_check_subprog_call(struct bpf_verifier_env *env, int subprog, + struct bpf_reg_state *regs); int btf_check_kfunc_arg_match(struct bpf_verifier_env *env, const struct btf *btf, u32 func_id, struct bpf_reg_state *regs, diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 903719b89238..eca9ea78ee5f 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -6170,7 +6170,8 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, const struct btf *btf, u32 func_id, struct bpf_reg_state *regs, bool ptr_to_mem_ok, - u32 kfunc_flags) + u32 kfunc_flags, + bool processing_call) { enum bpf_prog_type prog_type = resolve_prog_type(env->prog); bool rel = false, kptr_get = false, trusted_arg = false; @@ -6356,7 +6357,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, reg_ref_tname); return -EINVAL; } - } else if (ptr_to_mem_ok) { + } else if (ptr_to_mem_ok && processing_call) { const struct btf_type *resolve_ret; u32 type_size; @@ -6431,7 +6432,7 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, return rel ? ref_regno : 0; } -/* Compare BTF of a function with given bpf_reg_state. +/* Compare BTF of a function declaration with given bpf_reg_state. * Returns: * EFAULT - there is a verifier bug. Abort verification. * EINVAL - there is a type mismatch or BTF is not available. @@ -6458,7 +6459,50 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog, return -EINVAL; is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL; - err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, 0); + err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, 0, false); + + /* Compiler optimizations can remove arguments from static functions + * or mismatched type can be passed into a global function. + * In such cases mark the function as unreliable from BTF point of view. + */ + if (err) + prog->aux->func_info_aux[subprog].unreliable = true; + return err; +} + +/* Compare BTF of a function call with given bpf_reg_state. + * Returns: + * EFAULT - there is a verifier bug. Abort verification. + * EINVAL - there is a type mismatch or BTF is not available. + * 0 - BTF matches with what bpf_reg_state expects. + * Only PTR_TO_CTX and SCALAR_VALUE states are recognized. + * + * NOTE: the code is duplicated from btf_check_subprog_arg_match() + * because btf_check_func_arg_match() is still doing both. Once that + * function is split in 2, we can call from here btf_check_subprog_arg_match() + * first, and then treat the calling part in a new code path. + */ +int btf_check_subprog_call(struct bpf_verifier_env *env, int subprog, + struct bpf_reg_state *regs) +{ + struct bpf_prog *prog = env->prog; + struct btf *btf = prog->aux->btf; + bool is_global; + u32 btf_id; + int err; + + if (!prog->aux->func_info) + return -EINVAL; + + btf_id = prog->aux->func_info[subprog].type_id; + if (!btf_id) + return -EFAULT; + + if (prog->aux->func_info_aux[subprog].unreliable) + return -EINVAL; + + is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL; + err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, 0, true); /* Compiler optimizations can remove arguments from static functions * or mismatched type can be passed into a global function. @@ -6474,7 +6518,7 @@ int btf_check_kfunc_arg_match(struct bpf_verifier_env *env, struct bpf_reg_state *regs, u32 kfunc_flags) { - return btf_check_func_arg_match(env, btf, func_id, regs, true, kfunc_flags); + return btf_check_func_arg_match(env, btf, func_id, regs, true, kfunc_flags, true); } /* Convert BTF of a function into bpf_reg_state if possible diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 0194a36d0b36..d27fae3ce949 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6626,7 +6626,7 @@ static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn func_info_aux = env->prog->aux->func_info_aux; if (func_info_aux) is_global = func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL; - err = btf_check_subprog_arg_match(env, subprog, caller->regs); + err = btf_check_subprog_call(env, subprog, caller->regs); if (err == -EFAULT) return err; if (is_global) {