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 5367BECAAD5 for ; Mon, 5 Sep 2022 12:33:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238241AbiIEMdT (ORCPT ); Mon, 5 Sep 2022 08:33:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36444 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237714AbiIEMb7 (ORCPT ); Mon, 5 Sep 2022 08:31:59 -0400 Received: from mail-ed1-x54a.google.com (mail-ed1-x54a.google.com [IPv6:2a00:1450:4864:20::54a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E82806170D for ; Mon, 5 Sep 2022 05:26:49 -0700 (PDT) Received: by mail-ed1-x54a.google.com with SMTP id y12-20020a056402358c00b00448898f1c33so5692365edc.7 for ; Mon, 05 Sep 2022 05:26:49 -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=THOF30VtPA03HguE2vHQscvu4ZTBh5MWS0Wvqn4CdmFennnT2MwMnV9TcDZ3iHNp+s GIFt6P3re2Xo+37u/v00Y9DHfFIunA33ANa8bO9IuXi1k0z7jcjjiC1Qs1OqFW9GRw+H NE01mSjr6C9GGNwYYEPh7ZecXNqKtBXVTf5e4tlGS8oJ11WGhPU/7O8qaTlZ7kHXGZXr nv54U87Qubi0ceB7OERr7dnfX9ZRb6Ez6oDMpF+0xoUm5aualihiUUnnVv0ssiVkIzsf p/1s9yIn41sKfV1mVxEOL51ABsyyowCV9IdnoM8lSsY7waAb7T8vnpeJ9C3teWfyXNpp hOrA== 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=vRbpqsDIHDQCcATu6bzwH4ThLbn5QHfXutC2X7HPrl6Z7MgxeS9gf1I3eH8D5/BuNn UAQq1TvWUcWbClx3wNMc51McipVZCM2tV0CkfVfepBiQDKYjGtFSyd65fyjskoDglkOk qsIcRIL2KpFuTsf3EX0I72Ceb7dNnBuSiH9Em5knyIAOsGE8De1kCYRBUmJ1016afufb rBYAPcJRb/gpp5ru6wympjIFMtyi13ACw5bjrz9xluiY3OcCtq5zVji/5hmiixYAQchq 1Gj+PX17tQBtnYc3WTABYg02NzsOjiul3sXL8vSdPPonYrc8yIgW7ZugmH/Yi7fGZlSI VKHA== X-Gm-Message-State: ACgBeo3Wq0snrUfLTI2J19U8LJi3QsCZh7v7XTeDjCnHMXlmEL/3AcLn 8ZClW24wuT3pvGiuJN+0mYm6R4L5ay4= X-Google-Smtp-Source: AA6agR4vM0zsIKH75s7RCEaW6zrpgK+jiBpEwRdOSTxPxJ6LYkLuc7HHV+OetDykyKOVYyXQay+1ci6hfI4= X-Received: from glider.muc.corp.google.com ([2a00:79e0:9c:201:b808:8d07:ab4a:554c]) (user=glider job=sendgmr) by 2002:aa7:cb87:0:b0:43b:e650:6036 with SMTP id r7-20020aa7cb87000000b0043be6506036mr44091595edt.350.1662380807787; Mon, 05 Sep 2022 05:26:47 -0700 (PDT) Date: Mon, 5 Sep 2022 14:24:48 +0200 In-Reply-To: <20220905122452.2258262-1-glider@google.com> Mime-Version: 1.0 References: <20220905122452.2258262-1-glider@google.com> X-Mailer: git-send-email 2.37.2.789.g6183377224-goog Message-ID: <20220905122452.2258262-41-glider@google.com> Subject: [PATCH v6 40/44] 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 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 , 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-kernel@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