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 X-Spam-Level: X-Spam-Status: No, score=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B69AC43381 for ; Tue, 26 Feb 2019 10:47:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1C680217F9 for ; Tue, 26 Feb 2019 10:47:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="iHt4QD/j" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727762AbfBZKq7 (ORCPT ); Tue, 26 Feb 2019 05:46:59 -0500 Received: from mail.skyhub.de ([5.9.137.197]:60262 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727286AbfBZKq6 (ORCPT ); Tue, 26 Feb 2019 05:46:58 -0500 Received: from zn.tnic (p200300EC2BCDB2001DA4ECEFA9208567.dip0.t-ipconnect.de [IPv6:2003:ec:2bcd:b200:1da4:ecef:a920:8567]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 105711EC023E; Tue, 26 Feb 2019 11:46:57 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1551178017; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=UtRKe1UZfbyXC/+t4KcHfOTMhZy9W6j2yJlBltm8d1Y=; b=iHt4QD/j8+og9z4jXS29xHFtYGpZWd2WzxK24iCYXZv4fQoq2WCE17cQfxHSUMm1l5eShu o06T9ZyTpj5EobODyCUhuF0MVNJ/fzD8J5FdkPcj2l4zs1ZojY+hGSAB/SZ4haUb5jMYFO 8xRVn+Dlgh16/+a47ulMu4qjo2Z3IQs= Date: Tue, 26 Feb 2019 11:46:53 +0100 From: Borislav Petkov To: Pingfan Liu Cc: x86@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Baoquan He , Will Deacon , Nicolas Pitre , Chao Fan , "Kirill A. Shutemov" , Ard Biesheuvel , LKML Subject: Re: [PATCH] x86/boot/KASLR: skip the specified crashkernel reserved region Message-ID: <20190226104653.GB14836@zn.tnic> References: <1551081596-2856-1-git-send-email-kernelfans@gmail.com> <20190225094522.GC26145@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 26, 2019 at 11:08:42AM +0800, Pingfan Liu wrote: > I follow Baoquan's opinion. Due to the randomness caused by KASLR, a > user may be surprised to find crashkernel=x@y not working sometime. And she/he will get told in dmesg that the allocation failed. > If kernel can help them out of this corner automatically, then no > need to bother them with the message to use alternative method > crashkernel=M. Anyway it is a cheap method already used by other > options like hugepages and memmap in handle_mem_options(). > If commitment, then do it without failure. Or just removing > crashkernel=x@y option on x86. I can't parse what you're trying to say here but let me repeat myself: specifying a crashkernel region should not have an influence on KASLR because this way you limit the kernel where it selects the offset. It should be other other way around: KASLR offset should be selected and *then* crashkernel region. IOW, KASLR offset selection needs to have higher priority than crashkernel region selection. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.