From patchwork Tue Nov 15 21:19:01 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dmitry Safonov X-Patchwork-Id: 13044181 X-Patchwork-Delegate: kuba@kernel.org 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 8D9D6C4332F for ; Tue, 15 Nov 2022 21:20:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232142AbiKOVT5 (ORCPT ); Tue, 15 Nov 2022 16:19:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45256 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231230AbiKOVTu (ORCPT ); Tue, 15 Nov 2022 16:19:50 -0500 Received: from mail-wr1-x432.google.com (mail-wr1-x432.google.com [IPv6:2a00:1450:4864:20::432]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1836621E27 for ; Tue, 15 Nov 2022 13:19:46 -0800 (PST) Received: by mail-wr1-x432.google.com with SMTP id g12so26360084wrs.10 for ; Tue, 15 Nov 2022 13:19:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arista.com; s=google; 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=G6ZrelBNbx4bHqPFCl+9tJGrR84oe90P9c4JQMnU//c=; b=JEiTnfyG7jVn1GJy603cURHFeY1WtTxd95lLwGzpaA8HBNnXKesxowihb3ga39IPKr dS5gw1ezZx4dCaWPIAoHblLuwwFa6ESLDtWGU0E0Ok22CK32mdOJtxTg78+U4HkxGv8q y5Pn2DaPOFVFX/NDzqa+wg9sbjgYg1BDrSBkL0RGFRFGcUGOelgL132hPXG0Fny9hhGI tvgtu1d6G2g0fgsL/ThFkBdPrNOzJ9XQIJMtO1gIZ7b15+v0bRb5bQ4shpCXKN6bEmJz TbF8pwAK2SxsONFHVj/j2l1iXpbz8BLy2ORo0gkpaTyy0WLlzkiOOj6/nbupYYZderOi lCTA== 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=G6ZrelBNbx4bHqPFCl+9tJGrR84oe90P9c4JQMnU//c=; b=SOR8/Uza78ll68PhMumfh1lHybRbYSuGa8pEsjiG2NbD3sjm713mn9Frd4PpoDs0eP +7vB/hG9j6untv2G01yeQw1QGOv2a7zBi+5V+zzulQXb7ys0k+YNacHOgx1z2Z1FlgO2 oKO9kJhrTN/g0fzctHS+Y1MUazqWGlf+5Nv1Pfvob8fGV2NkxuIAOc+PCWXAyJIj/75i 1IfVlAwoDaUsTPVwLO7exqfMMlaclK/zzKYzrXloNcTsiGGo27PaGruu2rABsnL8y5fX Id1UMCZqq8GD4CJ2CiBmqMnw6F/FJSC7NOPj6jqKRC6K9xb88Q98wJvcKUy0SoudWeSp NVvA== X-Gm-Message-State: ANoB5pnb0MXEkTl0hkYBbafh6kIOWcM3LRRiM0jTjxOtD6ZwbX12pV9j 9ii+FbyRgdT1aBIkoiLUvIz+cg== X-Google-Smtp-Source: AA0mqf6ot1+pW00qvrkf/vvbjKqUy0/Nsglu2a7sKnGP3DS2KJSGUcA4Re4Z5gF68zjEj6eMwE5YFA== X-Received: by 2002:a05:6000:61a:b0:241:6e0a:bfe6 with SMTP id bn26-20020a056000061a00b002416e0abfe6mr12006959wrb.34.1668547154291; Tue, 15 Nov 2022 13:19:14 -0800 (PST) Received: from Mindolluin.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id n41-20020a05600c502900b003c65c9a36dfsm17201487wmr.48.2022.11.15.13.19.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Nov 2022 13:19:13 -0800 (PST) From: Dmitry Safonov To: linux-kernel@vger.kernel.org, David Ahern , Eric Dumazet , Peter Zijlstra Cc: Dmitry Safonov , Ard Biesheuvel , Bob Gilligan , "David S. Miller" , Dmitry Safonov <0x7f454c46@gmail.com>, Francesco Ruggeri , Hideaki YOSHIFUJI , Jakub Kicinski , Jason Baron , Josh Poimboeuf , Paolo Abeni , Salam Noureddine , Steven Rostedt , netdev@vger.kernel.org Subject: [PATCH v4 1/5] jump_label: Prevent key->enabled int overflow Date: Tue, 15 Nov 2022 21:19:01 +0000 Message-Id: <20221115211905.1685426-2-dima@arista.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221115211905.1685426-1-dima@arista.com> References: <20221115211905.1685426-1-dima@arista.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 1. With CONFIG_JUMP_LABEL=n static_key_slow_inc() doesn't have any protection against key->enabled refcounter overflow. 2. With CONFIG_JUMP_LABEL=y static_key_slow_inc_cpuslocked() still may turn the refcounter negative as (v + 1) may overflow. key->enabled is indeed a ref-counter as it's documented in multiple places: top comment in jump_label.h, Documentation/staging/static-keys.rst, etc. As -1 is reserved for static key that's in process of being enabled, functions would break with negative key->enabled refcount: - for CONFIG_JUMP_LABEL=n negative return of static_key_count() breaks static_key_false(), static_key_true() - the ref counter may become 0 from negative side by too many static_key_slow_inc() calls and lead to use-after-free issues. These flaws result in that some users have to introduce an additional mutex and prevent the reference counter from overflowing themselves, see bpf_enable_runtime_stats() checking the counter against INT_MAX / 2. Prevent the reference counter overflow by checking if (v + 1) > 0. Change functions API to return whether the increment was successful. Signed-off-by: Dmitry Safonov --- include/linux/jump_label.h | 19 +++++++++++--- kernel/jump_label.c | 54 +++++++++++++++++++++++++++++--------- 2 files changed, 57 insertions(+), 16 deletions(-) diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h index 570831ca9951..c0a02d4c2ea2 100644 --- a/include/linux/jump_label.h +++ b/include/linux/jump_label.h @@ -224,9 +224,9 @@ extern bool arch_jump_label_transform_queue(struct jump_entry *entry, enum jump_label_type type); extern void arch_jump_label_transform_apply(void); extern int jump_label_text_reserved(void *start, void *end); -extern void static_key_slow_inc(struct static_key *key); +extern bool static_key_slow_inc(struct static_key *key); extern void static_key_slow_dec(struct static_key *key); -extern void static_key_slow_inc_cpuslocked(struct static_key *key); +extern bool static_key_slow_inc_cpuslocked(struct static_key *key); extern void static_key_slow_dec_cpuslocked(struct static_key *key); extern int static_key_count(struct static_key *key); extern void static_key_enable(struct static_key *key); @@ -278,10 +278,21 @@ static __always_inline bool static_key_true(struct static_key *key) return false; } -static inline void static_key_slow_inc(struct static_key *key) +static inline bool static_key_slow_inc(struct static_key *key) { + int v; + STATIC_KEY_CHECK_USE(key); - atomic_inc(&key->enabled); + /* + * Prevent key->enabled getting negative to follow the same semantics + * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment. + */ + v = atomic_read(&key->enabled); + do { + if (v < 0 || (v + 1) < 0) + return false; + } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1))); + return true; } static inline void static_key_slow_dec(struct static_key *key) diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 4d6c6f5f60db..677a6674c130 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -113,9 +113,38 @@ int static_key_count(struct static_key *key) } EXPORT_SYMBOL_GPL(static_key_count); -void static_key_slow_inc_cpuslocked(struct static_key *key) +/*** + * static_key_fast_inc_not_negative - adds a user for a static key + * @key: static key that must be already enabled + * + * The caller must make sure that the static key can't get disabled while + * in this function. It doesn't patch jump labels, only adds a user to + * an already enabled static key. + * + * Returns true if the increment was done. + */ +static bool static_key_fast_inc_not_negative(struct static_key *key) { + int v; + STATIC_KEY_CHECK_USE(key); + /* + * Negative key->enabled has a special meaning: it sends + * static_key_slow_inc() down the slow path, and it is non-zero + * so it counts as "enabled" in jump_label_update(). Note that + * atomic_inc_unless_negative() checks >= 0, so roll our own. + */ + v = atomic_read(&key->enabled); + do { + if (v <= 0 || (v + 1) < 0) + return false; + } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1))); + + return true; +} + +bool static_key_slow_inc_cpuslocked(struct static_key *key) +{ lockdep_assert_cpus_held(); /* @@ -124,15 +153,9 @@ void static_key_slow_inc_cpuslocked(struct static_key *key) * jump_label_update() process. At the same time, however, * the jump_label_update() call below wants to see * static_key_enabled(&key) for jumps to be updated properly. - * - * So give a special meaning to negative key->enabled: it sends - * static_key_slow_inc() down the slow path, and it is non-zero - * so it counts as "enabled" in jump_label_update(). Note that - * atomic_inc_unless_negative() checks >= 0, so roll our own. */ - for (int v = atomic_read(&key->enabled); v > 0; ) - if (likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1))) - return; + if (static_key_fast_inc_not_negative(key)) + return true; jump_label_lock(); if (atomic_read(&key->enabled) == 0) { @@ -144,16 +167,23 @@ void static_key_slow_inc_cpuslocked(struct static_key *key) */ atomic_set_release(&key->enabled, 1); } else { - atomic_inc(&key->enabled); + if (WARN_ON_ONCE(!static_key_fast_inc_not_negative(key))) { + jump_label_unlock(); + return false; + } } jump_label_unlock(); + return true; } -void static_key_slow_inc(struct static_key *key) +bool static_key_slow_inc(struct static_key *key) { + bool ret; + cpus_read_lock(); - static_key_slow_inc_cpuslocked(key); + ret = static_key_slow_inc_cpuslocked(key); cpus_read_unlock(); + return ret; } EXPORT_SYMBOL_GPL(static_key_slow_inc);