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 7F234C433EF for ; Wed, 29 Sep 2021 18:54:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 627E061390 for ; Wed, 29 Sep 2021 18:54:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346362AbhI2S4j (ORCPT ); Wed, 29 Sep 2021 14:56:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49056 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346253AbhI2S4i (ORCPT ); Wed, 29 Sep 2021 14:56:38 -0400 Received: from mail-pl1-x636.google.com (mail-pl1-x636.google.com [IPv6:2607:f8b0:4864:20::636]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9693BC061764 for ; Wed, 29 Sep 2021 11:54:57 -0700 (PDT) Received: by mail-pl1-x636.google.com with SMTP id j15so2181301plh.7 for ; Wed, 29 Sep 2021 11:54:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=8+uJcBBc/PF7ems2z5fw4m588jWE79HAklefzm/UZpA=; b=jUKnSXoA0hVODkS6t3osdG2XYk+v1gSULRVbnIZ9NcZh4ZpOliivKVPuRpp/UlzKhh AbAGzhdYgAFxFcXd7rtQC4jDpvDc26ThZ27hDgqIxJg/E3s6vOblrrvcj45Gi0/6cPpw q2WLquH9eoGvFWwMXjEu5YoLIYzPRTV+vvS4w= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=8+uJcBBc/PF7ems2z5fw4m588jWE79HAklefzm/UZpA=; b=qR3urM6Rz7zwNcOhqX9T4B27DbPCfnL6/HoIEN4jLAl9tuqidCT5HWBD3dnvesiXuo ZkuRU+eRcWNkgt9yKBj06gNv5ydWWQV2Wo6edWikRIQKz9CZqr6Baf7FsJPKH8TsrsV2 zN3Tbvm0wBlE1yDPoFWjlezaShUIlpazuHe3EBHchdXxRSC/8e4ZllfnJ76XkHrGY5/f tnxRmaLtca4jCq3HPzzH6LZctwpHbrIEGDtHk2pQGlE4IOA1JXGxRGOlWziYBgHiH3gM oYAFeQZEuzBfEZIk695hvnhXlHD56cwt8ZFiU1yHCRtipA+JBLsz5lylxhF24W2Os2QA HZGg== X-Gm-Message-State: AOAM532LEpYFOZiU8H2VfTP2L/dAbE1j3pVBvWCq9Q9P+4IZWTf2yngY k6m3ENIaLUfSpUSB4UJ2mzpTyg== X-Google-Smtp-Source: ABdhPJzMCh/F5SF+Yhv5xgUAe1RpRTKX6R9v+nOxJt1NfhIE0v6dfSR2DW4sq15+zE5QfL0u0Kpdvg== X-Received: by 2002:a17:90a:304:: with SMTP id 4mr8095556pje.124.1632941697076; Wed, 29 Sep 2021 11:54:57 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id c206sm480031pfc.220.2021.09.29.11.54.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Sep 2021 11:54:56 -0700 (PDT) Date: Wed, 29 Sep 2021 11:54:55 -0700 From: Kees Cook To: Josh Poimboeuf Cc: Mark Rutland , Vito Caputo , Jann Horn , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Jens Axboe , Peter Zijlstra , Stefan Metzmacher , Andy Lutomirski , Lai Jiangshan , Christian Brauner , Andrew Morton , "Kenta.Tada@sony.com" , Daniel Bristot de Oliveira , Michael =?iso-8859-1?Q?Wei=DF?= , Anand K Mistry , Alexey Gladkov , Michal Hocko , Helge Deller , Dave Hansen , Andrea Righi , Ohhoon Kwon , Kalesh Singh , YiFei Zhu , "Eric W. Biederman" , Qi Zheng , linux-kernel@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] proc: Disable /proc/$pid/wchan Message-ID: <202109291152.681444A135@keescook> References: <20210923233105.4045080-1-keescook@chromium.org> <20210923234917.pqrxwoq7yqnvfpwu@shells.gnugeneration.com> <20210924002230.sijoedia65hf5bj7@shells.gnugeneration.com> <202109231814.FD09DBAD3@keescook> <20210924135424.GA33573@C02TD0UTHF1T.local> <202109240716.A0792BE46@keescook> <20210927090337.GB1131@C02TD0UTHF1T.local> <202109271103.4E15FC0@keescook> <20210927205056.jjdlkof5w6fs5wzw@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210927205056.jjdlkof5w6fs5wzw@treble> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Sep 27, 2021 at 01:50:56PM -0700, Josh Poimboeuf wrote: > On Mon, Sep 27, 2021 at 11:07:27AM -0700, Kees Cook wrote: > > On Mon, Sep 27, 2021 at 10:03:51AM +0100, Mark Rutland wrote: > > > On Fri, Sep 24, 2021 at 07:26:22AM -0700, Kees Cook wrote: > > > > On Fri, Sep 24, 2021 at 02:54:24PM +0100, Mark Rutland wrote: > > > > > On Thu, Sep 23, 2021 at 06:16:16PM -0700, Kees Cook wrote: > > > > > > On Thu, Sep 23, 2021 at 05:22:30PM -0700, Vito Caputo wrote: > > > > > > > Instead of unwinding stacks maybe the kernel should be sticking an > > > > > > > entrypoint address in the current task struct for get_wchan() to > > > > > > > access, whenever userspace enters the kernel? > > > > > > > > > > > > wchan is supposed to show where the kernel is at the instant the > > > > > > get_wchan() happens. (i.e. recording it at syscall entry would just > > > > > > always show syscall entry.) > > > > > > > > > > It's supposed to show where a blocked task is blocked; the "wait > > > > > channel". > > > > > > > > > > I'd wanted to remove get_wchan since it requires cross-task stack > > > > > walking, which is generally painful. > > > > > > > > Right -- this is the "fragile" part I'm worried about. > > > > I'd like to clarify this concern first -- is the proposed fix actually > > fragile? Because I think we'd be better off just restoring behavior than > > trying to invent new behavior... > > > > i.e. Josh, Jann, do you see any issues with Qi Zheng's fix here: > > https://lore.kernel.org/all/20210924062006.231699-4-keescook@chromium.org/ > > Even with that patch, it doesn't lock the task's runqueue before reading > the stack, so there's still the possibility of the task running on > another CPU and the unwinder going off the rails a bit, which might be > used by an attacker in creative ways similar to the /proc//stack > vulnerability Jann mentioned earlier. Since I think we're considering get_wchan() to be slow-path, can we just lock the runqueue and use arch_stack_walk_reliable()? -- Kees Cook