From patchwork Wed Nov 23 17:38:55 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dmitry Safonov X-Patchwork-Id: 13054037 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 166A6C433FE for ; Wed, 23 Nov 2022 17:39:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239137AbiKWRjV (ORCPT ); Wed, 23 Nov 2022 12:39:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58676 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239069AbiKWRjL (ORCPT ); Wed, 23 Nov 2022 12:39:11 -0500 Received: from mail-wr1-x42b.google.com (mail-wr1-x42b.google.com [IPv6:2a00:1450:4864:20::42b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DFB718FB29 for ; Wed, 23 Nov 2022 09:39:09 -0800 (PST) Received: by mail-wr1-x42b.google.com with SMTP id v1so30457525wrt.11 for ; Wed, 23 Nov 2022 09:39:09 -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=r5XPjM3RgE/cH2+A7+UFbzbdCk3mTFWCKPug1l8jbA0=; b=GiH4RbqJTKN/mly4lBU/H75GpRlBlxb0RYHmBN8b2PiA+WFBtoiaTYIY3iGo9JAh+N 3yPIiTFK5IwgKSZQvTymUaj9+FkwBORkQwhT9t2dWn/CoBR/wVQZUVeA797cKjK7x0gU APJXLW4Lc3ZVJMaaNWFbkrANbfIW43Gt5aCsbvCXV46a35pg9J7gudgfVxlW91qZB7kO 2ZY9eiMCD4F6073w+qH1/q3oLh/EaAXBbtHencOPgM/JpCQHx5wNDTIEZGycGbEASSLq z83KNrqZhUtMFdMdpr7hCitWRjEyuNU2Q35T06OSebu9NMWezsQ5zA8ou/FjGvYE7w91 G8jg== 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=r5XPjM3RgE/cH2+A7+UFbzbdCk3mTFWCKPug1l8jbA0=; b=0KDth4ygnRUCFSg6G/ivB8hazoCOiJQZ8PADxDXrlyfbshzSxXfXNxVDL8W44sSPRn btl0JY9msezYQWOX6Oxf4YBpuT5P4JlXT3HM/WKYYo1S8xTzAEaZ+32RISabeP7GDB71 DUNIndO5HaWQf1tXDhHi7OVR5rC3sbaB16JNxkQxkG4Nq75V87iSEjNvIQ67YcLBK1qx y6OKwmOtbxZqN+PopcWE34EWF8K6PGyu52h1d//Ev0lgxNTll+rnpfzd9HTGoQRrTkA2 5tqjbTaCjz1r/lOZOK6cLl1WDrgX0k75BAjUsbHkC9q0jnoBcFU1ZOMSW6F5dzWG49jw hxnw== X-Gm-Message-State: ANoB5pkYWGOet56VekeDi8LwloS0OVvquGWe7UdPBuuvwKopabmPD6/Z TFrsIMJz3Uh/OzC+3cc55G2tTA== X-Google-Smtp-Source: AA0mqf4WB//HRR7o8qsoYAXb9nei3HeIprtyCEwvLNr2Ci0zo6e2hcRvR3VFc7MtiiWtYdN31IomYw== X-Received: by 2002:adf:edd1:0:b0:241:7d0a:65ef with SMTP id v17-20020adfedd1000000b002417d0a65efmr10818977wro.491.1669225148331; Wed, 23 Nov 2022 09:39:08 -0800 (PST) Received: from Mindolluin.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id v10-20020adfe28a000000b0023647841c5bsm17464636wri.60.2022.11.23.09.39.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Nov 2022 09:39:07 -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 v6 1/5] jump_label: Prevent key->enabled int overflow Date: Wed, 23 Nov 2022 17:38:55 +0000 Message-Id: <20221123173859.473629-2-dima@arista.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221123173859.473629-1-dima@arista.com> References: <20221123173859.473629-1-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 Acked-by: Jakub Kicinski Acked-by: Peter Zijlstra (Intel) --- include/linux/jump_label.h | 21 +++++++++++--- kernel/jump_label.c | 56 ++++++++++++++++++++++++++++++-------- 2 files changed, 61 insertions(+), 16 deletions(-) diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h index 570831ca9951..4e968ebadce6 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 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 bool static_key_fast_inc_not_disabled(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 static_key *key) return false; } -static inline void static_key_slow_inc(struct static_key *key) +static inline bool static_key_fast_inc_not_disabled(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; } +#define static_key_slow_inc(key) static_key_fast_inc_not_disabled(key) 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..d9c822bbffb8 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -113,9 +113,40 @@ 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_disabled - 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. Unlike refcount_t the ref counter + * is not saturated, but will fail to increment on overflow. + */ +bool static_key_fast_inc_not_disabled(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; +} +EXPORT_SYMBOL_GPL(static_key_fast_inc_not_disabled); + +bool static_key_slow_inc_cpuslocked(struct static_key *key) +{ lockdep_assert_cpus_held(); /* @@ -124,15 +155,9 @@ 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_disabled(key)) + return true; jump_label_lock(); if (atomic_read(&key->enabled) == 0) { @@ -144,16 +169,23 @@ 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_disabled(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);