From patchwork Thu Nov 17 22:54:56 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: 13047434 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 36FBBC4332F for ; Thu, 17 Nov 2022 22:56:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234884AbiKQW4E (ORCPT ); Thu, 17 Nov 2022 17:56:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53254 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235058AbiKQWzz (ORCPT ); Thu, 17 Nov 2022 17:55:55 -0500 Received: from mail-pg1-x543.google.com (mail-pg1-x543.google.com [IPv6:2607:f8b0:4864:20::543]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9C10413E28 for ; Thu, 17 Nov 2022 14:55:52 -0800 (PST) Received: by mail-pg1-x543.google.com with SMTP id o13so3426698pgu.7 for ; Thu, 17 Nov 2022 14:55:52 -0800 (PST) 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=+ol7OxizXuiJ4eB7qeHuriIXAY7pywx1ZJI0gazh/20=; b=CEHiUJDt73p8YSq6fZGyoRPpWD6+/OAH+maYcCBLSD+zDeKXxWzvPXxSYeTZi+nldz M9Zj/cFXBvkYReSVnGwWQbbSO4pf16jUiP39xLtdrE0HZ3hb6CpHa5GVqqYcYVFJloHM qZ0N1cCd3l6L0nGfTSu+BhVKFa+CjGtw52U4lC62sAWOK8evWDT3V+bRBnkQ1tDaCFgf w32UvgpbL/dAxWksTqEd25dsg6kgVaXXI2Jx07CpQBqlwksyvsqzRH0HG41FuOdpwHB0 Lz1EClyYiY8EmxdEU54RYM1EYtKuS8p5BFuDtlz8RRh4EZQPrpad/3rfTOSXD/euKo9X Qhow== 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=+ol7OxizXuiJ4eB7qeHuriIXAY7pywx1ZJI0gazh/20=; b=Kv71+VImJaEWXGh8iDTODcLvbEDM2hCNU2quyYNBn6BisZeD+orTx2lOogrQYBwoN7 F7TNB/41A69kEeXsd+eV/fNstb9plIsYs2cv4Fsx8tRJH2oJzQk5Q1QSmxAzTReRSlnL eWVhVavvtOCAQU13k9wK1/XqhtdvI6QY6LeiZ9NYHRT0rrpF8RLSFOeM+3z5+/AGzwiq huhjW/YJCHR23SEsmW7qP1PWgWqDHugYS4Y7kKMj74fweiyc1yzSBVDzElQ/tutlbOhW 2l4tSCDTCUac8cHsJti7488GSGg73rUgfsIfIcGFa/vvonaf+wwRCROnlP9A3wmdXuai eTpA== X-Gm-Message-State: ANoB5plZzwSmVnm65hD/5evUo69OQD9/L1egGegsHd/csq+DkF4YgBAO PXfsi9a0RBisbxNDDmbV9E50aD34xtc= X-Google-Smtp-Source: AA0mqf5f3mG9rOJHY3+s6yhaZL4QTLx6FrXHxaPcqIpJdtYh0FoG77WKDH8lnvEBVp2qY0+oEuOpAQ== X-Received: by 2002:a62:3142:0:b0:56d:8d19:f331 with SMTP id x63-20020a623142000000b0056d8d19f331mr5097692pfx.7.1668725751232; Thu, 17 Nov 2022 14:55:51 -0800 (PST) Received: from localhost ([2409:40f4:8:955c:5484:8048:c08:7b3]) by smtp.gmail.com with ESMTPSA id q13-20020aa7960d000000b0057253eb631dsm1694331pfg.46.2022.11.17.14.55.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Nov 2022 14:55:50 -0800 (PST) From: Kumar Kartikeya Dwivedi To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Dave Marchevsky Subject: [PATCH bpf-next v9 09/23] bpf: Allow locking bpf_spin_lock global variables Date: Fri, 18 Nov 2022 04:24:56 +0530 Message-Id: <20221117225510.1676785-10-memxor@gmail.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221117225510.1676785-1-memxor@gmail.com> References: <20221117225510.1676785-1-memxor@gmail.com> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=7353; i=memxor@gmail.com; h=from:subject; bh=6Vv4lEhpsQX066e3Wnco5QRfk4WP+T5sUnI+NWbYFw4=; b=owEBbQKS/ZANAwAIAUzgyIZIvxHKAcsmYgBjdrkb8Zv5F6jnmv0dZ31LuaSqMWJy1JocMzVB/Fne /JTeMQSJAjMEAAEIAB0WIQRLvip+Buz51YI8YRFM4MiGSL8RygUCY3a5GwAKCRBM4MiGSL8Rysh9D/ wOaBppX4R8XmSWgw3YACFxggiYoXdJCcqVawKGf4Hykye/n0692eV9B1MClQodDBW3kGLaUzToMFU/ n+ICsuRFl3JE5yoz5Jt8XvJ2qQEaDA+dOiZXTIRY86FmT4DAIpU32GjNwSHbbJZ88FywYHypjPyz4x FHVJTnwfCc7S5tTce5tlUJHHxNfTp/W2m5H85fFy1idQjnXfH+odZAfuGeNlUSSiJlwVEQ15Pwg34N amQrR2iGffJvro3t9h+1RRHdKDR8sCV4THJsLU/cqlBdSN/uVcXfeXrxBWb/h1rB1JbkaqVNCe7ewV j9oWZfuP/fsUEDkKggcAYTwpFrz7XfNOQkfEtiC89c+foewBX+NEZiCfB22FZNLn+8tg0G+YJYGXT5 FjIS83SlfBh+/Jja1nqxJjI3HoArgoBjwJQKTGv7E11H3VN+6VQWHh8cHJyzdCQMZW6zw4yk2uwMYa Ke4hSPrD4hdI0KTCHO+CQzVP9MUY+hKKExViKD/a9Gnv8sWe/eWnXMLwtqBAX0c+R17rfd8mhzbRQz /p83JyQYcBdm9/kjtq6fWMEU6x+iUXXErYp+DtWEZQgDDibNobwNAX85mtUMtG51IUavBF4S2yb/2i nn1xI9TgLoaOFcFifa/198ay86rFSNZAmOBb+tI8G5LqLiumLHeZUy/OGpUA== 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 Global variables reside in maps accessible using direct_value_addr callbacks, so giving each load instruction's rewrite a unique reg->id disallows us from holding locks which are global. The reason for preserving reg->id as a unique value for registers that may point to spin lock is that two separate lookups are treated as two separate memory regions, and any possible aliasing is ignored for the purposes of spin lock correctness. This is not great especially for the global variable case, which are served from maps that have max_entries == 1, i.e. they always lead to map values pointing into the same map value. So refactor the active_spin_lock into a 'active_lock' structure which represents the lock identity, and instead of the reg->id, remember two fields, a pointer and the reg->id. The pointer will store reg->map_ptr or reg->btf. It's only necessary to distinguish for the id == 0 case of global variables, but always setting the pointer to a non-NULL value and using the pointer to check whether the lock is held simplifies code in the verifier. This is generic enough to allow it for global variables, map lookups, and allocated objects at the same time. Note that while whether a lock is held can be answered by just comparing active_lock.ptr to NULL, to determine whether the register is pointing to the same held lock requires comparing _both_ ptr and id. Finally, as a result of this refactoring, pseudo load instructions are not given a unique reg->id, as they are doing lookup for the same map value (max_entries is never greater than 1). Essentially, we consider that the tuple of (ptr, id) will always be unique for any kind of argument to bpf_spin_{lock,unlock}. Note that this can be extended in the future to also remember offset used for locking, so that we can introduce multiple bpf_spin_lock fields in the same allocation. Signed-off-by: Kumar Kartikeya Dwivedi --- include/linux/bpf_verifier.h | 16 +++++++++++++- kernel/bpf/verifier.c | 41 ++++++++++++++++++++++++------------ 2 files changed, 43 insertions(+), 14 deletions(-) diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 1a32baa78ce2..3770bb1a6f62 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -323,7 +323,21 @@ struct bpf_verifier_state { u32 branches; u32 insn_idx; u32 curframe; - u32 active_spin_lock; + /* For every reg representing a map value of allocated object pointer, + * we consider the tuple of (ptr, id) for them to be unique in verifier + * context and conside them to not alias each other for the purposes of + * tracking lock state. + */ + struct { + /* This can either be reg->map_ptr or reg->btf. If ptr is NULL, + * there's no active lock held, and other fields have no + * meaning. If non-NULL, it indicates that a lock is held and + * id member has the reg->id of the register which can be >= 0. + */ + void *ptr; + /* This will be reg->id */ + u32 id; + } active_lock; bool speculative; /* first and last insn idx of this verifier state */ diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8eddecfc3a5e..b231abbeaf55 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1215,7 +1215,8 @@ static int copy_verifier_state(struct bpf_verifier_state *dst_state, } dst_state->speculative = src->speculative; dst_state->curframe = src->curframe; - dst_state->active_spin_lock = src->active_spin_lock; + dst_state->active_lock.ptr = src->active_lock.ptr; + dst_state->active_lock.id = src->active_lock.id; dst_state->branches = src->branches; dst_state->parent = src->parent; dst_state->first_insn_idx = src->first_insn_idx; @@ -5590,7 +5591,7 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state * Since only one bpf_spin_lock is allowed the checks are simpler than * reg_is_refcounted() logic. The verifier needs to remember only * one spin_lock instead of array of acquired_refs. - * cur_state->active_spin_lock remembers which map value element or allocated + * cur_state->active_lock remembers which map value element or allocated * object got locked and clears it after bpf_spin_unlock. */ static int process_spin_lock(struct bpf_verifier_env *env, int regno, @@ -5639,22 +5640,35 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno, return -EINVAL; } if (is_lock) { - if (cur->active_spin_lock) { + if (cur->active_lock.ptr) { verbose(env, "Locking two bpf_spin_locks are not allowed\n"); return -EINVAL; } - cur->active_spin_lock = reg->id; + if (map) + cur->active_lock.ptr = map; + else + cur->active_lock.ptr = btf; + cur->active_lock.id = reg->id; } else { - if (!cur->active_spin_lock) { + void *ptr; + + if (map) + ptr = map; + else + ptr = btf; + + if (!cur->active_lock.ptr) { verbose(env, "bpf_spin_unlock without taking a lock\n"); return -EINVAL; } - if (cur->active_spin_lock != reg->id) { + if (cur->active_lock.ptr != ptr || + cur->active_lock.id != reg->id) { verbose(env, "bpf_spin_unlock of different lock\n"); return -EINVAL; } - cur->active_spin_lock = 0; + cur->active_lock.ptr = NULL; + cur->active_lock.id = 0; } return 0; } @@ -10616,8 +10630,8 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn) insn->src_reg == BPF_PSEUDO_MAP_IDX_VALUE) { dst_reg->type = PTR_TO_MAP_VALUE; dst_reg->off = aux->map_off; - if (btf_record_has_field(map->record, BPF_SPIN_LOCK)) - dst_reg->id = ++env->id_gen; + WARN_ON_ONCE(map->max_entries != 1); + /* We want reg->id to be same (0) as map_value is not distinct */ } else if (insn->src_reg == BPF_PSEUDO_MAP_FD || insn->src_reg == BPF_PSEUDO_MAP_IDX) { dst_reg->type = CONST_PTR_TO_MAP; @@ -10695,7 +10709,7 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn) return err; } - if (env->cur_state->active_spin_lock) { + if (env->cur_state->active_lock.ptr) { verbose(env, "BPF_LD_[ABS|IND] cannot be used inside bpf_spin_lock-ed region\n"); return -EINVAL; } @@ -11961,7 +11975,8 @@ static bool states_equal(struct bpf_verifier_env *env, if (old->speculative && !cur->speculative) return false; - if (old->active_spin_lock != cur->active_spin_lock) + if (old->active_lock.ptr != cur->active_lock.ptr || + old->active_lock.id != cur->active_lock.id) return false; /* for states to be equal callsites have to be the same @@ -12606,7 +12621,7 @@ static int do_check(struct bpf_verifier_env *env) return -EINVAL; } - if (env->cur_state->active_spin_lock && + if (env->cur_state->active_lock.ptr && (insn->src_reg == BPF_PSEUDO_CALL || insn->imm != BPF_FUNC_spin_unlock)) { verbose(env, "function calls are not allowed while holding a lock\n"); @@ -12643,7 +12658,7 @@ static int do_check(struct bpf_verifier_env *env) return -EINVAL; } - if (env->cur_state->active_spin_lock) { + if (env->cur_state->active_lock.ptr) { verbose(env, "bpf_spin_unlock is missing\n"); return -EINVAL; }