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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 594C3C433FE for ; Tue, 5 Oct 2021 10:59:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4871461139 for ; Tue, 5 Oct 2021 10:59:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234366AbhJELBr (ORCPT ); Tue, 5 Oct 2021 07:01:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51980 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234314AbhJELBl (ORCPT ); Tue, 5 Oct 2021 07:01:41 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A5A48C061762 for ; Tue, 5 Oct 2021 03:59:50 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id y16-20020a2586d0000000b005b752db8f97so17520725ybm.18 for ; Tue, 05 Oct 2021 03:59:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=kUUBsv4TZ+s6mxdftD0CD4qwCQSHLXZlKlhseQGR4HI=; b=rEZQ6gHEpvFmnU3JJ2KadwYQcU/JSBtWD9kFPefHUesYhWgD+zWgArmWGmRaRUoRtk VDKK8Clkd1IXKKUXE7uGOCQiR/a8VLzgq14e4z3yFqsyEMB8J+yA2fLfPmDZ1cgwu7IA hxWJQYHsv0nxh98TCmcq99vXZHi81m/dePuKk+O8qPlob0rH4fJEMk6xuMnX/JJw3dJK w+/HEGUet8yHVB4XffG2TDeLzpNjvUlMe1PO08esWDxORp5yjfb6ZGwfrmryknbMGoVf IweJBPgmp5Gr9RwWgQoSzOGRDC7O4CUXO3DyTZtoWRfCwGXfU1t0hBdbgyv0icSZytvz vwrw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=kUUBsv4TZ+s6mxdftD0CD4qwCQSHLXZlKlhseQGR4HI=; b=w+bCqcpEvI4f2hNHalsTvRTeNOdYP8JDK6oPE7OOMoy9qCV7FkuuTxVJZic1qiB9uP hRRxzSMN2PKcSOxfA9HWwNz+AlaXszi8bTm/dnjIVhozMSU38bYG4lfPW26ZL/EELmsc ITDDV4/gZrR+PJv6ihdPnaXwrfR22Eb1HOecJpTUviR4eOdnzcvVpGE0RiRAEuGJ103E cbr2tUImv5OvL2135uwVT7k4Sdjxnc8DWtKnMQPXG+ypyk4YxjrbJuxp9CZc84ZqqLVM /eFZqVZHZUsES7pAcQ8iri01MccZrF+L64myOGFuD7V5ImFuWxXgSSXjR2dqjpAGaDDd p4Zg== X-Gm-Message-State: AOAM531QtDxwcDpgY3yC+e8JgZmkyrGvjMmcaYFkZEY5CIvw1HakJ7O/ gtVXYR1wpX9wwmO3ZrV2qTkXlfPPAw== X-Google-Smtp-Source: ABdhPJxRi+Ql2gxjFY5+cYUsl3wIa8YCDZUdUIEKXnqibIFEFifviy3RA6gYeFrxOW2C0fskgkXzwtNlZw== X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:e44f:5054:55f8:fcb8]) (user=elver job=sendgmr) by 2002:a5b:f03:: with SMTP id x3mr20807187ybr.546.1633431589883; Tue, 05 Oct 2021 03:59:49 -0700 (PDT) Date: Tue, 5 Oct 2021 12:58:45 +0200 In-Reply-To: <20211005105905.1994700-1-elver@google.com> Message-Id: <20211005105905.1994700-4-elver@google.com> Mime-Version: 1.0 References: <20211005105905.1994700-1-elver@google.com> X-Mailer: git-send-email 2.33.0.800.g4c38ced690-goog Subject: [PATCH -rcu/kcsan 03/23] kcsan: Avoid checking scoped accesses from nested contexts From: Marco Elver To: elver@google.com, "Paul E . McKenney" Cc: Alexander Potapenko , Boqun Feng , Borislav Petkov , Dmitry Vyukov , Ingo Molnar , Josh Poimboeuf , Mark Rutland , Peter Zijlstra , Thomas Gleixner , Waiman Long , Will Deacon , kasan-dev@googlegroups.com, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Avoid checking scoped accesses from nested contexts (such as nested interrupts or in scheduler code) which share the same kcsan_ctx. This is to avoid detecting false positive races of accesses in the same thread with currently scoped accesses: consider setting up a watchpoint for a non-scoped (normal) access that also "conflicts" with a current scoped access. In a nested interrupt (or in the scheduler), which shares the same kcsan_ctx, we cannot check scoped accesses set up in the parent context -- simply ignore them in this case. With the introduction of kcsan_ctx::disable_scoped, we can also clean up kcsan_check_scoped_accesses()'s recursion guard, and do not need to modify the list's prev pointer. Signed-off-by: Marco Elver --- include/linux/kcsan.h | 1 + kernel/kcsan/core.c | 18 +++++++++++++++--- 2 files changed, 16 insertions(+), 3 deletions(-) diff --git a/include/linux/kcsan.h b/include/linux/kcsan.h index fc266ecb2a4d..13cef3458fed 100644 --- a/include/linux/kcsan.h +++ b/include/linux/kcsan.h @@ -21,6 +21,7 @@ */ struct kcsan_ctx { int disable_count; /* disable counter */ + int disable_scoped; /* disable scoped access counter */ int atomic_next; /* number of following atomic ops */ /* diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index e34a1710b7bc..bd359f8ee63a 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -204,15 +204,17 @@ check_access(const volatile void *ptr, size_t size, int type, unsigned long ip); static noinline void kcsan_check_scoped_accesses(void) { struct kcsan_ctx *ctx = get_ctx(); - struct list_head *prev_save = ctx->scoped_accesses.prev; struct kcsan_scoped_access *scoped_access; - ctx->scoped_accesses.prev = NULL; /* Avoid recursion. */ + if (ctx->disable_scoped) + return; + + ctx->disable_scoped++; list_for_each_entry(scoped_access, &ctx->scoped_accesses, list) { check_access(scoped_access->ptr, scoped_access->size, scoped_access->type, scoped_access->ip); } - ctx->scoped_accesses.prev = prev_save; + ctx->disable_scoped--; } /* Rules for generic atomic accesses. Called from fast-path. */ @@ -465,6 +467,15 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned goto out; } + /* + * Avoid races of scoped accesses from nested interrupts (or scheduler). + * Assume setting up a watchpoint for a non-scoped (normal) access that + * also conflicts with a current scoped access. In a nested interrupt, + * which shares the context, it would check a conflicting scoped access. + * To avoid, disable scoped access checking. + */ + ctx->disable_scoped++; + /* * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's * runtime is entered for every memory access, and potentially useful @@ -578,6 +589,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned if (!kcsan_interrupt_watcher) local_irq_restore(irq_flags); kcsan_restore_irqtrace(current); + ctx->disable_scoped--; out: user_access_restore(ua_flags); } -- 2.33.0.800.g4c38ced690-goog