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 2A03AC63798 for ; Mon, 23 Nov 2020 13:23:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CAA492075A for ; Mon, 23 Nov 2020 13:23:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="i/NiRwJL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732325AbgKWNXO (ORCPT ); Mon, 23 Nov 2020 08:23:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731551AbgKWNXH (ORCPT ); Mon, 23 Nov 2020 08:23:07 -0500 Received: from mail-qt1-x849.google.com (mail-qt1-x849.google.com [IPv6:2607:f8b0:4864:20::849]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 78901C0613CF for ; Mon, 23 Nov 2020 05:23:07 -0800 (PST) Received: by mail-qt1-x849.google.com with SMTP id b10so13476664qtb.16 for ; Mon, 23 Nov 2020 05:23:07 -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=t3/TP+aeGOrrYIoQsNoDeJwx7Pw16YuC73tVL3PfhCA=; b=i/NiRwJL0aJluZg5rY8KsCulRKgc+UIE+SwCY7gUAxgnPZ1DfIy6g+p0imKJ5QTcXP rHXztNfebMNml29UfXm28PtR8/4STJ4lZ5Zndp7+57cfD6oYhY5k7r4uxl2nLK2NFrzb GVmbvB5Jn6H8aq49me8QP2RKQzFDwSpcos382cVgK8t/+hWCBgKCkrrv3G9jyOHYPDP+ 9YTddxXG16wpfVLk6VXqatc4mquxTBkAQ4hPcNdiUqPfeiOLjt4scvJrn91LLrwRW9s9 SRnhWSXu0XrUiJF6hWAajTwzYHYcMPjg5d5iiyWD3h5m93ag9utQnds5R+bI5o1PuBWj bnzQ== 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=t3/TP+aeGOrrYIoQsNoDeJwx7Pw16YuC73tVL3PfhCA=; b=KndAaUtmhmMGU4Ly0sIr7vixNRnE5ViHw1+BC41ItNYqTg4q+axo+qm4tGZtx+B+pA JSyV/e1nNzOdLY+OFHHkNEwQ1V9NjIzxcycQ5PrqhWGbTfT5r7cgKbmzeVMlAZz+JpvZ hMbtCTf73VVeO/c1JdZPOq8APHd4plYkb4MrMsncBNdp586JykJaTEg13C//kpD6tzOS AAOvljWMmYEcuo0S97J3ZTiUF4mXLTkuKtZ/NI//nMdGHRRmd7mp8M2Z9ruIN77FUNwC bpb/HXfRbBkVN2a5lnlnuLUf+qVNzgksYdZcfLLtcYelYwQQWXHtEez/AFMgnfnSecGz xhcw== X-Gm-Message-State: AOAM531WsCq0Hy//9T85iO4B9n0R7TlrliwlSy+a3iCVQ09rZ6Cj5iav SuHlrnabcw0ALHjhUcg+IQixkvmJ3Q== X-Google-Smtp-Source: ABdhPJyi3sQ41pGPGDDNk6GR3kRu1nWMRGVpWjvKEjGZvzaSlIDMjPCg7+tYy46kUauCfGMXwtMg/n0wlg== 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:a0c:b5a6:: with SMTP id g38mr13953823qve.31.1606137786488; Mon, 23 Nov 2020 05:23:06 -0800 (PST) Date: Mon, 23 Nov 2020 14:23:00 +0100 Message-Id: <20201123132300.1759342-1-elver@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.29.2.454.gaff20da3a2-goog Subject: [PATCH v2] kcsan: Avoid scheduler recursion by using non-instrumented preempt_{disable,enable}() 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() and preempt_enable() 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 --- v2: * Update comment to also point out preempt_enable(). --- kernel/kcsan/core.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index 3994a217bde7..10513f3e2349 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -284,10 +284,19 @@ 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 versions of + * preempt_disable() and preempt_enable() 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); } -- 2.29.2.454.gaff20da3a2-goog