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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 08E52ECAAA1 for ; Thu, 15 Sep 2022 15:12:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231221AbiIOPMO (ORCPT ); Thu, 15 Sep 2022 11:12:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48608 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230423AbiIOPKY (ORCPT ); Thu, 15 Sep 2022 11:10:24 -0400 Received: from mail-ed1-x549.google.com (mail-ed1-x549.google.com [IPv6:2a00:1450:4864:20::549]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8254D9E10E for ; Thu, 15 Sep 2022 08:06:26 -0700 (PDT) Received: by mail-ed1-x549.google.com with SMTP id z13-20020a05640240cd00b0045276a79364so5706559edb.2 for ; Thu, 15 Sep 2022 08:06:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date; bh=Rbxz0iuc7RXxWgIfjeSrHOuiWEHvXH2VAJuclXEfLdg=; b=F6VwgljKSoHlmWj1nWyCtFBHI2b5B8DMZ6H1olBVWsiyfT2kbw7W/bawpY6tA8zayB THwH3bKPewMxmxrhbJdq+mZdumidYxMIcUtzSGYEkAasnxQOXeSE7IjjawVZVIn2zcXQ r1YsO97BGqmMH/3Gm3SPgEFLbDSNRdcBrXoh3uNQ2BkTLA6uRpOGDFXhN9pCl9ZI7NBZ xhhcFg1UVJA4C2HyIq9LT8Fw+KPyPlGxH/UCui6KY5gucTlsnsRb7V38I53MLrTmhqTr tJkPsqtR6gQh2kMAprFeLbJIRRB1FXqX6TCmSGetbahnUDYy2pQaPR875kzYJHfpMY4q Y0EA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date; bh=Rbxz0iuc7RXxWgIfjeSrHOuiWEHvXH2VAJuclXEfLdg=; b=oBC20FrJg3p2IGOaaEyymKVboVZRJFNyhl/v9rZQPXy/SWS0Q4Fobbsl8img3OkisH DHANl703iVd0mKmAfIlQKiGvYXu4OQi1kVjnG6sJFEPnZV3cCq8ese4oTd+oNVKZnKzx YuKXwm6400uwQvORE1RjP9K9XUdAjTeV4qLuMzds84dahJFJliBQ514rt7EWR881A/Vd RWWgguymGCcxXrDVkiZHy0uvL9CXnun8NRtAzs2dv8PBz0SjJR0zKP6WOuvSpjGsmLgQ Q0E47ABNGs134gQWmnhLfa7uBW9ZxGWuwkykhI0oyA/E9O/LTuN9TNUMsMfpzb2f6UBF +7Tg== X-Gm-Message-State: ACrzQf1f3pASnNRUrcC+chhAETAzsETTy9jPJ2mD3/JpQ3Z5+KSeNe3/ J3pUgFq7cXvgb3thoqJlZyCuPSZr80Q= X-Google-Smtp-Source: AMsMyM6h5O71+6F4YlSosQQjOpItz2+q8/2EVZ42RobJy7VoqbBopgEvjyHEgtHeKPds8m8QA7fCze15fV4= X-Received: from glider.muc.corp.google.com ([2a00:79e0:9c:201:686d:27b5:495:85b7]) (user=glider job=sendgmr) by 2002:a05:6402:270f:b0:451:b5bd:95dd with SMTP id y15-20020a056402270f00b00451b5bd95ddmr251653edd.215.1663254384829; Thu, 15 Sep 2022 08:06:24 -0700 (PDT) Date: Thu, 15 Sep 2022 17:04:13 +0200 In-Reply-To: <20220915150417.722975-1-glider@google.com> Mime-Version: 1.0 References: <20220915150417.722975-1-glider@google.com> X-Mailer: git-send-email 2.37.2.789.g6183377224-goog Message-ID: <20220915150417.722975-40-glider@google.com> Subject: [PATCH v7 39/43] x86: kmsan: don't instrument stack walking functions From: Alexander Potapenko To: glider@google.com Cc: Alexander Viro , Alexei Starovoitov , Andrew Morton , Andrey Konovalov , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Christoph Hellwig , Christoph Lameter , David Rientjes , Dmitry Vyukov , Eric Biggers , Eric Dumazet , Greg Kroah-Hartman , Herbert Xu , Ilya Leoshkevich , Ingo Molnar , Jens Axboe , Joonsoo Kim , Kees Cook , Marco Elver , Mark Rutland , Matthew Wilcox , "Michael S. Tsirkin" , Pekka Enberg , Peter Zijlstra , Petr Mladek , Stephen Rothwell , Steven Rostedt , Thomas Gleixner , Vasily Gorbik , Vegard Nossum , Vlastimil Babka , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org Upon function exit, KMSAN marks local variables as uninitialized. Further function calls may result in the compiler creating the stack frame where these local variables resided. This results in frame pointers being marked as uninitialized data, which is normally correct, because they are not stack-allocated. However stack unwinding functions are supposed to read and dereference the frame pointers, in which case KMSAN might be reporting uses of uninitialized values. To work around that, we mark update_stack_state(), unwind_next_frame() and show_trace_log_lvl() with __no_kmsan_checks, preventing all KMSAN reports inside those functions and making them return initialized values. Signed-off-by: Alexander Potapenko --- Link: https://linux-review.googlesource.com/id/I6550563768fbb08aa60b2a96803675dcba93d802 --- arch/x86/kernel/dumpstack.c | 6 ++++++ arch/x86/kernel/unwind_frame.c | 11 +++++++++++ 2 files changed, 17 insertions(+) diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index afae4dd774951..476eb504084e4 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -177,6 +177,12 @@ static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs, } } +/* + * This function reads pointers from the stack and dereferences them. The + * pointers may not have their KMSAN shadow set up properly, which may result + * in false positive reports. Disable instrumentation to avoid those. + */ +__no_kmsan_checks static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs, unsigned long *stack, const char *log_lvl) { diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c index 8e1c50c86e5db..d8ba93778ae32 100644 --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -183,6 +183,16 @@ static struct pt_regs *decode_frame_pointer(unsigned long *bp) } #endif +/* + * While walking the stack, KMSAN may stomp on stale locals from other + * functions that were marked as uninitialized upon function exit, and + * now hold the call frame information for the current function (e.g. the frame + * pointer). Because KMSAN does not specifically mark call frames as + * initialized, false positive reports are possible. To prevent such reports, + * we mark the functions scanning the stack (here and below) with + * __no_kmsan_checks. + */ +__no_kmsan_checks static bool update_stack_state(struct unwind_state *state, unsigned long *next_bp) { @@ -250,6 +260,7 @@ static bool update_stack_state(struct unwind_state *state, return true; } +__no_kmsan_checks bool unwind_next_frame(struct unwind_state *state) { struct pt_regs *regs; -- 2.37.2.789.g6183377224-goog