Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932720AbaLAW7k (ORCPT ); Mon, 1 Dec 2014 17:59:40 -0500 Received: from mail-oi0-f48.google.com ([209.85.218.48]:47670 "EHLO mail-oi0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932458AbaLAW7j (ORCPT ); Mon, 1 Dec 2014 17:59:39 -0500 MIME-Version: 1.0 In-Reply-To: References: Date: Mon, 1 Dec 2014 14:59:38 -0800 X-Google-Sender-Auth: 7HIfF4y2P_1YxUZzOJYCwdBguQY Message-ID: Subject: Re: PROBLEM: [Launchpad #1396889] [Lenovo ThinkPad T400] kexec reboot fails From: Kees Cook To: MegaBrutal Cc: Linux kernel , Baoquan He , "x86@kernel.org" , "H. Peter Anvin" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 1, 2014 at 2:45 PM, MegaBrutal wrote: > 2014-12-01 7:32 GMT+01:00 MegaBrutal : >> [X.] Other notes, patches, fixes, workarounds: >> Downstream report (Ubuntu Launchpad): >> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1396889 >> >> With kernel bisection, I've found, the first bad commit is >> 8ab3820fd5b2896d66da7bb2a906bc382e63e7bc x86, kaslr: Return location >> from decompress_kernel >> which introduces KASLR. >> http://lkml.kernel.org/r/1381450698-28710-3-git-send-email-keescook@chromium.org >> >> The problem only presents itself when CONFIG_RANDOMIZE_BASE=y. >> >> For workaround, there is a "nokaslr" kernel parameter to disable the >> feature, even if the kernel was compiled with CONFIG_RANDOMIZE_BASE. > > Need to add: as I tested today, unfortunately the "nokaslr" kernel > option doesn't work around the bug. If a kernel was compiled with > CONFIG_RANDOMIZE_BASE, it won't properly kexec on my ThinkPad T400, > even if the "nokaslr" kernel option is provided! > > This could actually help to find the bug, as whatever bad happens must > happen before the kernel checks for the presence of the "nokaslr" > kernel parameter. I suspect you're encountering a subset of the same problems as described in this thread: https://lkml.org/lkml/2014/9/30/90 If you can test those patches, that may help demonstrate their utility. Thanks! -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/