From nobody Mon Apr 13 13:14:50 2026 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 085D2C433FE for ; Fri, 11 Nov 2022 21:23:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234113AbiKKVXn (ORCPT ); Fri, 11 Nov 2022 16:23:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48890 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233963AbiKKVXc (ORCPT ); Fri, 11 Nov 2022 16:23:32 -0500 Received: from mail-wr1-x42a.google.com (mail-wr1-x42a.google.com [IPv6:2a00:1450:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2CF069FF8 for ; Fri, 11 Nov 2022 13:23:31 -0800 (PST) Received: by mail-wr1-x42a.google.com with SMTP id l14so7977467wrw.2 for ; Fri, 11 Nov 2022 13:23:31 -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=/wqu7ka025DHmiQHo96XTmKANEmftj8UjKkUsPUJ5+A=; b=fxVJwfPadmX2Uf5lD3RgJFfhZGXHqr6rP7D8M4ssAK4uU5IWGA4BJkQKPdVttgZO+v uXmVGi6Qgm563iisXM1+ajmiPXYAsXb99/we41xRtyFyhDvvDRZC8JPD9I/7OpCUqjVj lUTPyvEtnEF6q4PNqyi0LwMAh7Ssg8QqgqdkV9Bx/xXvspGSWleBm83YkbIx7nY3+C+E ffQkoIU0G6sAtFXGMlkKE5hog0L+8Yj5cXwmrwtBijDE4XmlKDip1EhBxi1441SQ6taO 2fN94oJE07p69DqUZPt7ICKiGdM2wTBzV9ok2L80GKrDG8/3wzotNFYnYwAejO3PXXMk 6Lkw== 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=/wqu7ka025DHmiQHo96XTmKANEmftj8UjKkUsPUJ5+A=; b=i4HPrdA6/fqfXoWbOhL6FPVhzF9kmVLxJMoNazqasvtaStB6wQlWy1OoC2wCRgwKiL 5O42SluN2iD0pIPpSRp6PalkNTWXujXLyxd9XyWnEc54vL6q/46iCexlbfnaQR+ecbhI FFjp49EKA/fUJbQcUqhqIZ7+rR86drbArOOEN70K+18f4W38e6L05O2WaFJ0qRk4/wmH VNWfIzFY9WC3J+8PY1sDiAqg+eBtnOw8caS69BNZNO3VqJCVuTeYFmvHib02Ob2N1SjI rIjO5uLwz7HV56kYJ+wccsTJ/p0l1CXGHVS8m1MrKFZMslDFE2v3iTGuzNL3nHdMP6g7 o2Dg== X-Gm-Message-State: ANoB5pklEMQzSxBNnZ5gdMglEYBZyx8AcKVgPhITfpSVVdrdtUBMzSmZ Tci1OQcqUQInPFZHngaeAy0CGomAH/qR4A== X-Google-Smtp-Source: AA0mqf5qyVUOYbiavINF4aCT+lEdbutL4RcNHVO5ns2hb4bESLOXBnavZU1Tx0DyY7qe1LjOnH85mg== X-Received: by 2002:adf:f882:0:b0:236:8dd7:1919 with SMTP id u2-20020adff882000000b002368dd71919mr2114766wrp.242.1668201809379; Fri, 11 Nov 2022 13:23:29 -0800 (PST) Received: from Mindolluin.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id n18-20020a7bcbd2000000b003cf9bf5208esm9423281wmi.19.2022.11.11.13.23.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 11 Nov 2022 13:23:28 -0800 (PST) From: Dmitry Safonov To: linux-kernel@vger.kernel.org, David Ahern , Eric Dumazet Cc: Dmitry Safonov , Bob Gilligan , "David S. Miller" , Dmitry Safonov <0x7f454c46@gmail.com>, Francesco Ruggeri , Hideaki YOSHIFUJI , Jakub Kicinski , Paolo Abeni , Salam Noureddine , netdev@vger.kernel.org, Ard Biesheuvel , Jason Baron , Josh Poimboeuf , Peter Zijlstra , Steven Rostedt Subject: [PATCH v3 1/3] jump_label: Prevent key->enabled int overflow Date: Fri, 11 Nov 2022 21:23:18 +0000 Message-Id: <20221111212320.1386566-2-dima@arista.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221111212320.1386566-1-dima@arista.com> References: <20221111212320.1386566-1-dima@arista.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 1. With CONFIG_JUMP_LABEL=3Dn static_key_slow_inc() doesn't have any protection against key->enabled refcounter overflow. 2. With CONFIG_JUMP_LABEL=3Dy 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=3Dn 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. While at here, provide static_key_fast_inc() helper that does ref counter increment in atomic fashion (without grabbing cpus_read_lock() on CONFIG_JUMP_LABEL=3Dy). This is needed to add a new user for a static_key when the caller controls the lifetime of another user. The exact detail where it will be used: if a listen socket with TCP-MD5 key receives SYN packet that passes the verification and in result creates a request socket - it's all done from RX softirq. At that moment userspace can't lock the listen socket and remove that TCP-MD5 key, so the tcp_md5_needed static branch can't get disabled. But the refcounter of the static key needs to be adjusted to account for a new user (the request socket). Cc: Ard Biesheuvel Cc: Eric Dumazet Cc: Jason Baron Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: Steven Rostedt Signed-off-by: Dmitry Safonov --- include/linux/jump_label.h | 21 ++++++++++++--- kernel/jump_label.c | 54 ++++++++++++++++++++++++++++---------- 2 files changed, 57 insertions(+), 18 deletions(-) diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h index 570831ca9951..ced5b49d24b4 100644 --- a/include/linux/jump_label.h +++ b/include/linux/jump_label.h @@ -224,9 +224,10 @@ extern bool arch_jump_label_transform_queue(struct jum= p_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 bool static_key_fast_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); @@ -278,11 +279,23 @@ static __always_inline bool static_key_true(struct st= atic_key *key) return false; } =20 -static inline void static_key_slow_inc(struct static_key *key) +static inline bool static_key_fast_inc(struct static_key *key) { + int v, v1; + STATIC_KEY_CHECK_USE(key); - atomic_inc(&key->enabled); + /* + * Prevent key->enabled getting negative to follow the same semantics + * as for CONFIG_JUMP_LABEL=3Dy, see kernel/jump_label.c comment. + */ + for (v =3D atomic_read(&key->enabled); v >=3D 0 && (v + 1) > 0; v =3D v1)= { + v1 =3D atomic_cmpxchg(&key->enabled, v, v + 1); + if (likely(v1 =3D=3D v)) + return true; + } + return false; } +#define static_key_slow_inc(key) static_key_fast_inc(key) =20 static inline void static_key_slow_dec(struct static_key *key) { diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 714ac4c3b556..f2c1aa351d41 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -113,11 +113,38 @@ int static_key_count(struct static_key *key) } EXPORT_SYMBOL_GPL(static_key_count); =20 -void static_key_slow_inc_cpuslocked(struct static_key *key) +/*** + * static_key_fast_inc - 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. + */ +bool static_key_fast_inc(struct static_key *key) { int v, v1; =20 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 >=3D 0, so roll our own. + */ + for (v =3D atomic_read(&key->enabled); v > 0 && (v + 1) > 0; v =3D v1) { + v1 =3D atomic_cmpxchg(&key->enabled, v, v + 1); + if (likely(v1 =3D=3D v)) + return true; + } + return false; +} +EXPORT_SYMBOL_GPL(static_key_fast_inc); + +bool static_key_slow_inc_cpuslocked(struct static_key *key) +{ lockdep_assert_cpus_held(); =20 /* @@ -126,17 +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 >=3D 0, so roll our own. */ - for (v =3D atomic_read(&key->enabled); v > 0; v =3D v1) { - v1 =3D atomic_cmpxchg(&key->enabled, v, v + 1); - if (likely(v1 =3D=3D v)) - return; - } + if (static_key_fast_inc(key)) + return true; =20 jump_label_lock(); if (atomic_read(&key->enabled) =3D=3D 0) { @@ -148,16 +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(key))) { + jump_label_unlock(); + return false; + } } jump_label_unlock(); + return true; } =20 -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 =3D static_key_slow_inc_cpuslocked(key); cpus_read_unlock(); + return ret; } EXPORT_SYMBOL_GPL(static_key_slow_inc); =20 --=20 2.38.1