From patchwork Thu Nov 3 19:10:06 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kumar Kartikeya Dwivedi X-Patchwork-Id: 13030884 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 BAB00C433FE for ; Thu, 3 Nov 2022 19:11:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231182AbiKCTLk (ORCPT ); Thu, 3 Nov 2022 15:11:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53350 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231382AbiKCTLa (ORCPT ); Thu, 3 Nov 2022 15:11:30 -0400 Received: from mail-pf1-x444.google.com (mail-pf1-x444.google.com [IPv6:2607:f8b0:4864:20::444]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 28B6D1DA4A for ; Thu, 3 Nov 2022 12:11:30 -0700 (PDT) Received: by mail-pf1-x444.google.com with SMTP id y203so2519544pfb.4 for ; Thu, 03 Nov 2022 12:11:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=xWTuhUdTsoJJMSoUXUiqcLtS/v42WScBtGllQKlBmG8=; b=TjTpY/ZQAnu40D2SnEhJc2fvBa7Oqz7O8r9f3ddHrW2+mQTGEEsJraQqk6OQmFN+U5 /Hkil3epRGo83JcQFBLomZzTeOYU8cwruzMDs5xGK3H+Duy2PjUTgAdxMFdDFM18N0n7 kxFvrq/LYoCqkXZ5+V5f5aKocwlEfDYyYiUkX9HGWhl+JXzmfVaDaKeVs382S6zK+rmZ LPO6bqk0vR6u+uCKH4yo9PTgxHYi/h5J427GlZsmIIE+D9hbJRz4IM78kbcm/KhdHG3X CTbVkbFG15bzphYzHofKTWCriYBcsrJNU3ehasVEdvFF6xY2iKB7fhbgfWOwZrlFEtEs Or8Q== 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=xWTuhUdTsoJJMSoUXUiqcLtS/v42WScBtGllQKlBmG8=; b=b6hhmqrd82zvTkm6u6sdTx6TpvY4/NMj9U9bS6eudkueK76XV4u0nSRcxT1mR7rx6x R1QH9U26t/JV4X3f3zc2wQ7UPparkRPUjJgijUZVBl/YG/cCFks3eC8NXkXLrEMGYkKz loXDhEgDUOXj+OibyMNxBKjCsJeujCLhy4dh8Uo6D8NUc7s7MPRlyISJNFcf/iOpk0Ol tKjkMHcW9QeZmeRQ6Upd1I+Y5zcqJHU5jUz2OHsTBYqbvZvZHuyxErJUNeAH/1SmFvQO fRQNyY4H7pxxktNoT/bO0DuQTA/x5maOJFJi6IdAgLLa+JrYNiBhuG4gi7fqN7QAfv1V Aa8w== X-Gm-Message-State: ACrzQf2WMFxmQnr/yL+5I5j5U6kQx4yjIowV6owPrJNsrkfvQ236iK42 AeuQRfseH4jMEN23aWTakeOWXbq9YDHVkg== X-Google-Smtp-Source: AMsMyM7k/dBLZ6pSeQjAu/SN5Yak9qcwY2V+IUQMC3cpfSzvv6Gob42xTlCKjEWzEv/W5NBPw71VAw== X-Received: by 2002:a05:6a00:1f0e:b0:56e:1ce2:a4fd with SMTP id be14-20020a056a001f0e00b0056e1ce2a4fdmr8728669pfb.76.1667502689346; Thu, 03 Nov 2022 12:11:29 -0700 (PDT) Received: from localhost ([103.4.222.252]) by smtp.gmail.com with ESMTPSA id g9-20020a1709026b4900b001868981a18esm1061295plt.6.2022.11.03.12.11.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Nov 2022 12:11:28 -0700 (PDT) From: Kumar Kartikeya Dwivedi To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Dave Marchevsky , Delyan Kratunov Subject: [PATCH bpf-next v4 17/24] bpf: Support constant scalar arguments for kfuncs Date: Fri, 4 Nov 2022 00:40:06 +0530 Message-Id: <20221103191013.1236066-18-memxor@gmail.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221103191013.1236066-1-memxor@gmail.com> References: <20221103191013.1236066-1-memxor@gmail.com> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=6081; i=memxor@gmail.com; h=from:subject; bh=CZNnVG4cpb7gTpxmPgHM5Y8cbZqvBrdHtioKiFAhX70=; b=owEBbQKS/ZANAwAIAUzgyIZIvxHKAcsmYgBjZBIBHW4DihBG67QYjD2mQijkOvxnAyypCXtIBDEI 3Y5LhquJAjMEAAEIAB0WIQRLvip+Buz51YI8YRFM4MiGSL8RygUCY2QSAQAKCRBM4MiGSL8RyqgBD/ 4ouzl2MSSCOH6DZxlmSkW1a035kSpsfxYialxyCdQkskKnZq4X90XDwguWcfNNzpdAS1OKL8mUmIat hh1UO6RF2D6oy8cfMtkcbculEGpNqnR1DbABflSt61zfdLJ4+VX1xDwn9Qh6oJS22M6NAEJEcIcVTi 1k7iBbi9bZTR0uwSgwGi/kJNABGsveg20zJXGR/e3Mu97W+jt1W5n8sAe85X4ZjK84nzHeWk3heq30 T02VsPEtuOh92lTbRWSsPtlzqc3V6bJo5q0tk+0DQIXsVy0mpSgCSILEuziC6b9PPR8ljIqu7QBPHo ly+iNe1748sEtrMedNK4a0hzjuQc+tmL2iL1BU3ZMZq3jxv02oiG8S4jHqDOhq2rNa49+yifHRVTP/ 3lolBtq9MiZajMh4uojBw1qni9J8raW4h6d77iNTTUib+XXnqASXXYUDoli6XJ4L3HxcxvKOoDK1pG oSxPym6G9ashxmJfHXIi0DfuPQj4d4YegjU/DZX6dRQ8nUidWHnztCW4LcDMCuePA4aOKfOOHIIaum T3yqc96uBuy31QMFcenPmEGbjfGRb8qC3BEWIwAJVOWlsoIPonvlWA5O36yxzmfjswpNbYtQPV0SIO AlEte8+CMt23QVZlBXnFSXlrk+SlZz9VkGJfanxyon5gyeeAaQ/SYfjLICKQ== X-Developer-Key: i=memxor@gmail.com; a=openpgp; fpr=4BBE2A7E06ECF9D5823C61114CE0C88648BF11CA Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Allow passing known constant scalars as arguments to kfuncs that do not represent a size parameter. This makes the search pruning optimization of verifier more conservative for such kfunc calls, and each non-distinct argument is considered unequivalent. We will use this support to then expose a global bpf_kptr_alloc function where it takes the local type ID in program BTF, and returns a PTR_TO_BTF_ID to the local type. These will be called local kptrs, and allows programs to allocate their own objects. However, this is still not completely safe, as mark_chain_precision logic is buggy without more work when the constant argument is not a size, but still needs precise marker propagation for pruning checks. Next patch will fix this problem. Signed-off-by: Kumar Kartikeya Dwivedi --- Documentation/bpf/kfuncs.rst | 30 ++++++++++++++++++ kernel/bpf/verifier.c | 59 +++++++++++++++++++++++++++--------- 2 files changed, 75 insertions(+), 14 deletions(-) diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst index 0f858156371d..08f9a968d06d 100644 --- a/Documentation/bpf/kfuncs.rst +++ b/Documentation/bpf/kfuncs.rst @@ -72,6 +72,36 @@ argument as its size. By default, without __sz annotation, the size of the type of the pointer is used. Without __sz annotation, a kfunc cannot accept a void pointer. +2.2.1 __k Annotation +-------------------- + +This annotation is only understood for scalar arguments, where it indicates that +the verifier must check the scalar argument to be a known constant, which does +not indicate a size parameter. This distinction is important, as when the scalar +argument does not represent a size parameter, verifier is more conservative in +state search pruning and does not consider two arguments equivalent for safety +purposes if the already verified value was within range of the new one. + +This assumption holds well for sizes (as memory accessed within smaller bounds +in old verified state will also work for bigger bounds in current to be explored +state), but not for other constant arguments where each carries a distinct +semantic effect. + +An example is given below:: + + void *bpf_mem_alloc(u32 local_type_id__k) + { + ... + } + +Here, bpf_mem_alloc uses local_type_id argument to find out the size of that +type ID in program's BTF and return a sized pointer to it. Each type ID will +have a distinct size, hence it is crucial to treat each such call as distinct +when values don't match. + +Hence, whenever a constant scalar argument is accepted by a kfunc which is not a +size parameter, __k suffix must be used. + .. _BPF_kfunc_nodef: 2.3 Using an existing kernel function diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index effc417cc086..b22ad48bbecd 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7687,6 +7687,10 @@ struct bpf_kfunc_call_arg_meta { u8 release_regno; bool r0_rdonly; u64 r0_size; + struct { + u64 value; + bool found; + } arg_constant; }; static bool is_kfunc_acquire(struct bpf_kfunc_call_arg_meta *meta) @@ -7724,30 +7728,40 @@ static bool is_kfunc_arg_kptr_get(struct bpf_kfunc_call_arg_meta *meta, int arg) return arg == 0 && (meta->kfunc_flags & KF_KPTR_GET); } -static bool is_kfunc_arg_mem_size(const struct btf *btf, - const struct btf_param *arg, - const struct bpf_reg_state *reg) +static bool __kfunc_param_match_suffix(const struct btf *btf, + const struct btf_param *arg, + const char *suffix) { - int len, sfx_len = sizeof("__sz") - 1; - const struct btf_type *t; + int suffix_len = strlen(suffix), len; const char *param_name; - t = btf_type_skip_modifiers(btf, arg->type, NULL); - if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE) - return false; - /* In the future, this can be ported to use BTF tagging */ param_name = btf_name_by_offset(btf, arg->name_off); if (str_is_empty(param_name)) return false; len = strlen(param_name); - if (len < sfx_len) + if (len < suffix_len) return false; - param_name += len - sfx_len; - if (strncmp(param_name, "__sz", sfx_len)) + param_name += len - suffix_len; + return !strncmp(param_name, suffix, suffix_len); +} + +static bool is_kfunc_arg_mem_size(const struct btf *btf, + const struct btf_param *arg, + const struct bpf_reg_state *reg) +{ + const struct btf_type *t; + + t = btf_type_skip_modifiers(btf, arg->type, NULL); + if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE) return false; - return true; + return __kfunc_param_match_suffix(btf, arg, "__sz"); +} + +static bool is_kfunc_arg_sfx_constant(const struct btf *btf, const struct btf_param *arg) +{ + return __kfunc_param_match_suffix(btf, arg, "__k"); } static bool is_kfunc_arg_ret_buf_size(const struct btf *btf, @@ -8023,7 +8037,24 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ verbose(env, "R%d is not a scalar\n", regno); return -EINVAL; } - if (is_kfunc_arg_ret_buf_size(btf, &args[i], reg, "rdonly_buf_size")) { + if (is_kfunc_arg_sfx_constant(meta->btf, &args[i])) { + /* kfunc is already bpf_capable() only, no need + * to check it here. + */ + if (meta->arg_constant.found) { + verbose(env, "verifier internal error: only one constant argument permitted\n"); + return -EFAULT; + } + if (!tnum_is_const(reg->var_off)) { + verbose(env, "R%d must be a known constant\n", regno); + return -EINVAL; + } + ret = mark_chain_precision(env, regno); + if (ret < 0) + return ret; + meta->arg_constant.found = true; + meta->arg_constant.value = reg->var_off.value; + } else if (is_kfunc_arg_ret_buf_size(btf, &args[i], reg, "rdonly_buf_size")) { meta->r0_rdonly = true; is_ret_buf_sz = true; } else if (is_kfunc_arg_ret_buf_size(btf, &args[i], reg, "rdwr_buf_size")) {