From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-26.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4184FC2D0E4 for ; Tue, 17 Nov 2020 16:37:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C26BB217A0 for ; Tue, 17 Nov 2020 16:37:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="NgPOtLVr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728144AbgKQQg7 (ORCPT ); Tue, 17 Nov 2020 11:36:59 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33266 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726181AbgKQQg7 (ORCPT ); Tue, 17 Nov 2020 11:36:59 -0500 Received: from mail-wm1-x34a.google.com (mail-wm1-x34a.google.com [IPv6:2a00:1450:4864:20::34a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D017CC0613CF for ; Tue, 17 Nov 2020 08:36:58 -0800 (PST) Received: by mail-wm1-x34a.google.com with SMTP id 3so1997776wms.9 for ; Tue, 17 Nov 2020 08:36:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=1AB7jWGDKqYLUDgu1C5v3wJ4U1VEzQNUsWCkMQleGjc=; b=NgPOtLVr3vxHbX4TvNNxUpe6EqYYLOZmMZP5lXvsFtFkS9aHzMKXS4gXEjWyXvfhj6 lkxhDkZ5xXf3L8CJPu4KWEsmVjHlevFYkmL/PPwDPT+T1jKsW6cyQk/e5R/PCDkNu/20 t7pY1X0Ff7JUk1WD3ftXrt35oJ1ORgDP1Ml1EYKWYbLiYQGPuvXBue/X0syo1m4wnZzG Oe1Vi9NArJP9TgLAr+PDMuTKgnzPWywIlfF5EaqEzIqff3p0WRt9RVIS3kZWitWHDeoJ GnLmp1nrhNu3EFPvUxUpz1StQCort44URbqqWrhtPBnH5sHqpimJaOcFP/EysmRBmDlG cVlA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=1AB7jWGDKqYLUDgu1C5v3wJ4U1VEzQNUsWCkMQleGjc=; b=TwNF3LTtQ6FubfvDEMUhc/zpSoMR824Vq/ZPSd9MsFNrbb3eT73iEucdSPgAK6mljK O9MFdduD5lr2CjqZ6/KaTXk13dU0RHGIwR8pLDHGYDblV11TmUgvhFa2jgb7vjvR3V5r WsoMkrwGwfLkiIMFtsQWBL3qjpahtUgSHMM/wwvp9wF6oSgtc008UR4eOXvKkT8l25TA vDWS8OUE2S/bgXjmb1QmYiZFuUasrDDIInbTx9ZUy7aR4JMmv3i9V0oT7X3lVjkFR5Zx 8psbbOIoR3rKBfiYfywcQa0BjzkTeHnddvV/Mpiwk6oY4q/nYzVFaB8fcuQZGS7aPE3P qkOQ== X-Gm-Message-State: AOAM531Gkvc9enRcVOQCN2B1UE7bQmIJ5Q+2o+w5IuAlEfzVydoy/VJX hRH4hxqOR4XLFz6cfnJNuKprbAOCBA== X-Google-Smtp-Source: ABdhPJx+dUpTJoVqJNMHpC2Y4LofeI+h+gBPz+ugnc+RuKcKyfvLtiSI2Vf2z49tSNVd+vufXa9YG8PFQg== Sender: "elver via sendgmr" X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:f693:9fff:fef4:2449]) (user=elver job=sendgmr) by 2002:a1c:791a:: with SMTP id l26mr22568wme.1.1605631016587; Tue, 17 Nov 2020 08:36:56 -0800 (PST) Date: Tue, 17 Nov 2020 17:36:41 +0100 Message-Id: <20201117163641.3389352-1-elver@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.29.2.299.gdc1121823c-goog Subject: [PATCH] kcsan: Avoid scheduler recursion by using non-instrumented preempt_disable() From: Marco Elver To: elver@google.com, paulmck@kernel.org Cc: will@kernel.org, peterz@infradead.org, tglx@linutronix.de, mingo@kernel.org, mark.rutland@arm.com, boqun.feng@gmail.com, dvyukov@google.com, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When enabling KCSAN for kernel/sched (remove KCSAN_SANITIZE := n from kernel/sched/Makefile), with CONFIG_DEBUG_PREEMPT=y, we can observe recursion due to: check_access() [via instrumentation] kcsan_setup_watchpoint() reset_kcsan_skip() kcsan_prandom_u32_max() get_cpu_var() preempt_disable() preempt_count_add() [in kernel/sched/core.c] check_access() [via instrumentation] Avoid this by rewriting kcsan_prandom_u32_max() to only use safe versions of preempt_disable() that do not call into scheduler code. Note, while this currently does not affect an unmodified kernel, it'd be good to keep a KCSAN kernel working when KCSAN_SANITIZE := n is removed from kernel/sched/Makefile to permit testing scheduler code with KCSAN if desired. Fixes: cd290ec24633 ("kcsan: Use tracing-safe version of prandom") Signed-off-by: Marco Elver --- kernel/kcsan/core.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index 3994a217bde7..967b0b2f9d59 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -284,10 +284,18 @@ should_watch(const volatile void *ptr, size_t size, int type, struct kcsan_ctx * */ static u32 kcsan_prandom_u32_max(u32 ep_ro) { - struct rnd_state *state = &get_cpu_var(kcsan_rand_state); - const u32 res = prandom_u32_state(state); + struct rnd_state *state; + u32 res; + + /* + * Avoid recursion with scheduler by using non-tracing version of + * preempt_disable() that do not call into scheduler code. + */ + preempt_disable_notrace(); + state = raw_cpu_ptr(&kcsan_rand_state); + res = prandom_u32_state(state); + preempt_enable_no_resched_notrace(); - put_cpu_var(kcsan_rand_state); return (u32)(((u64) res * ep_ro) >> 32); } -- 2.29.2.299.gdc1121823c-goog