From patchwork Thu Nov 18 08:10:07 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marco Elver X-Patchwork-Id: 12626195 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 3AEB8C433FE for ; Thu, 18 Nov 2021 08:11:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 25C5161BD3 for ; Thu, 18 Nov 2021 08:11:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244268AbhKRIOP (ORCPT ); Thu, 18 Nov 2021 03:14:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42442 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244269AbhKRIOG (ORCPT ); Thu, 18 Nov 2021 03:14:06 -0500 Received: from mail-wr1-x449.google.com (mail-wr1-x449.google.com [IPv6:2a00:1450:4864:20::449]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E10C3C06120A for ; Thu, 18 Nov 2021 00:11:05 -0800 (PST) Received: by mail-wr1-x449.google.com with SMTP id q7-20020adff507000000b0017d160d35a8so877402wro.4 for ; Thu, 18 Nov 2021 00:11:05 -0800 (PST) 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=cCyxJnES0DWyrpQ2J5vRoZu9DlHTb3+fL88VjiCWbjg=; b=U6MOwm5YMGFgIxfJyMcfK1fy2ZzEMSWUD5qAdZAzplNRNP7y1WSuqURPPJGKJuCfyA tLjBC4LWDhIOvpwVSIWlN/7hCC7oDRSAEe3N5O7HXF2+1cysu+v/p1swtiItkjHcY2wA SKAtC33LlUoMSl910Qd33i8hqhUurSDnGqhxDtBZW1tDDEjYPrEDzYFu9Q7x85JMzCoO C4GIrFGrw7ORbcAqnDgrzvS/VicOAMv5s3BFyWUfDJ5iXC7yoZ6fi2//vKWqmvJb/Rk9 5nEe5UA0D42ee/7U1oYy4dTdtn5p8v8YxwHYhlqleHpsQAO2c7MYg8uQiOugGlxBUyBi uUUQ== 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=cCyxJnES0DWyrpQ2J5vRoZu9DlHTb3+fL88VjiCWbjg=; b=IxlEM3ZhpSXUfHECg7PodDdcwe+w0tFmvIA29bC8vJn3lQBfecW5WhI6dQxIM8/+v1 Xp0Zzb5klB2+yH4Jf0JRBv2kmS+cXIcNAco70WIg1aat5sKpdZrPFD6sD2uVCzlm0lgB o+DWlwnfsWrwPA+SUYO0iasxGAKUgcFro/2pqSK1LmkK1rezFVVRx4WuX46CCgxGlBaO JxgvZ8t9EqfGEEitLwEmYPflzhyepMd29XdX3YKBZc4Fg2epEBZymuANo910T5kfbDJn bEIkYu85yEsRu7zri739q6wIcqjqMsF9Rw1KetCJL3yVuvKphjVgLHk1+3RW0ZR/OTnN d6Bw== X-Gm-Message-State: AOAM5326fonjLYIrcJssUxZ3jOpukD1uCgvLEq4yk5OOx6S8afRhgNzo 7MP64BLPtgIuGY53HGPV7DXONZdFZA== X-Google-Smtp-Source: ABdhPJxkB593VfcNkLX9J9nVFwnAhaHJjUUwfmrh7gaZZX3OtssqlV/5En9lYvCkCZUZKU3Aqu91vbjvqg== X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:7155:1b7:fca5:3926]) (user=elver job=sendgmr) by 2002:a05:600c:3b20:: with SMTP id m32mr2109203wms.0.1637223063945; Thu, 18 Nov 2021 00:11:03 -0800 (PST) Date: Thu, 18 Nov 2021 09:10:07 +0100 In-Reply-To: <20211118081027.3175699-1-elver@google.com> Message-Id: <20211118081027.3175699-4-elver@google.com> Mime-Version: 1.0 References: <20211118081027.3175699-1-elver@google.com> X-Mailer: git-send-email 2.34.0.rc2.393.gf8c9666880-goog Subject: [PATCH v2 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 Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@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); }