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=-8.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 D1AFEC3A5A9 for ; Mon, 4 May 2020 10:41:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9C1A62073B for ; Mon, 4 May 2020 10:41:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="kuIp+12Q" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728157AbgEDKlf (ORCPT ); Mon, 4 May 2020 06:41:35 -0400 Received: from mail.skyhub.de ([5.9.137.197]:55946 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726445AbgEDKlf (ORCPT ); Mon, 4 May 2020 06:41:35 -0400 Received: from zn.tnic (p200300EC2F08AF00A9258889345EFBFA.dip0.t-ipconnect.de [IPv6:2003:ec:2f08:af00:a925:8889:345e:fbfa]) (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 DC0E51EC011B; Mon, 4 May 2020 12:41:33 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1588588894; 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=iRUNm3gcqi81lpr43dwmxdWf16YWxyP1UxTVlnpFzUU=; b=kuIp+12Q+Ly/02XXR6hpYKN7OouGtkNo7biM9HOEmVEhTzPn6oWp7JLSYxLEcLL7THnsuI uOJ/KMNOHqrpBJLxGMZrz6Dnr3mvcCxOKjbb+pFhKh3I/1xOg9r8213Q4Y8B7Cn3h6pD+d lUiNekNhlKGzhQzLbDWp8+pUbFsCGjw= Date: Mon, 4 May 2020 12:41:29 +0200 From: Borislav Petkov To: Joerg Roedel Cc: x86@kernel.org, hpa@zytor.com, Andy Lutomirski , Dave Hansen , Peter Zijlstra , Thomas Hellstrom , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , Kees Cook , David Rientjes , Cfir Cohen , Erdem Aktas , Masami Hiramatsu , Mike Stunes , Joerg Roedel , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v3 12/75] x86/boot/compressed/64: Switch to __KERNEL_CS after GDT is loaded Message-ID: <20200504104129.GD15046@zn.tnic> References: <20200428151725.31091-1-joro@8bytes.org> <20200428151725.31091-13-joro@8bytes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200428151725.31091-13-joro@8bytes.org> 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, Apr 28, 2020 at 05:16:22PM +0200, Joerg Roedel wrote: > From: Joerg Roedel > > When the pre-decompression code loads its first GDT in startup_64, it is > still running on the CS value of the previous GDT. In the case of SEV-ES > this is the EFI GDT. > > To make exception handling work (especially IRET) the CPU needs to > switch to a CS value in the current GDT, so jump to __KERNEL_CS after > the first GDT is loaded. > > Signed-off-by: Joerg Roedel > --- > arch/x86/boot/compressed/head_64.S | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S > index 4f7e6b84be07..6b11060c3a0f 100644 > --- a/arch/x86/boot/compressed/head_64.S > +++ b/arch/x86/boot/compressed/head_64.S > @@ -393,6 +393,14 @@ SYM_CODE_START(startup_64) > addq %rax, 2(%rax) > lgdt (%rax) > > + /* Reload CS so IRET returns to a CS actually in the GDT */ > + pushq $__KERNEL_CS > + leaq .Lon_kernel_cs(%rip), %rax > + pushq %rax > + lretq > + > +.Lon_kernel_cs: > + > /* > * paging_prepare() sets up the trampoline and checks if we need to > * enable 5-level paging. > -- So I'm thinking I should take this one even now on the grounds that it sanitizes CS to something known-good than what was there before and who knows what set it and loaded the kernel...? And that is a good thing in itself. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette