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 12E66C00140 for ; Tue, 26 Jul 2022 17:25:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235278AbiGZRZX (ORCPT ); Tue, 26 Jul 2022 13:25:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52936 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229738AbiGZRZU (ORCPT ); Tue, 26 Jul 2022 13:25:20 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6697B642C; Tue, 26 Jul 2022 10:25:19 -0700 (PDT) Received: from zn.tnic (p200300ea970f4ff2329c23fffea6a903.dip0.t-ipconnect.de [IPv6:2003:ea:970f:4ff2:329c:23ff:fea6:a903]) (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 7E2BA1EC0373; Tue, 26 Jul 2022 19:25:13 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1658856313; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Zc808cWbuiJ1LaEmAlRr5AvsxdqrezqcJtLhbo5Uy7g=; b=ql/OkaR/2POULdFAydeXv9SQYYLAW2Oguhc/zysyKU429tW8xTTiXOcCVj73rfKKSdqrp9 S2n5W66hmjC11W1t+j5O+pllUu0utmqWbzKTSg7rCsEUxTCKefdk+G0CusKKEjYT9YMGhP 1I2mP9ZoAv/WhylmeLh+Gcmv8J0BS9Q= Date: Tue, 26 Jul 2022 19:25:09 +0200 From: Borislav Petkov To: "Kirill A. Shutemov" Cc: Andy Lutomirski , Sean Christopherson , Andrew Morton , Joerg Roedel , Ard Biesheuvel , Andi Kleen , Kuppuswamy Sathyanarayanan , David Rientjes , Vlastimil Babka , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Paolo Bonzini , Ingo Molnar , Varad Gautam , Dario Faggioli , Dave Hansen , Mike Rapoport , David Hildenbrand , marcelo.cerri@canonical.com, tim.gardner@canonical.com, khalid.elmously@canonical.com, philip.cox@canonical.com, x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv7 10/14] x86/mm: Avoid load_unaligned_zeropad() stepping into unaccepted memory Message-ID: References: <20220614120231.48165-1-kirill.shutemov@linux.intel.com> <20220614120231.48165-11-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220614120231.48165-11-kirill.shutemov@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 14, 2022 at 03:02:27PM +0300, Kirill A. Shutemov wrote: > diff --git a/arch/x86/mm/unaccepted_memory.c b/arch/x86/mm/unaccepted_memory.c > index 1df918b21469..bcd56fe82b9e 100644 > --- a/arch/x86/mm/unaccepted_memory.c > +++ b/arch/x86/mm/unaccepted_memory.c > @@ -23,6 +23,38 @@ void accept_memory(phys_addr_t start, phys_addr_t end) > bitmap = __va(boot_params.unaccepted_memory); > range_start = start / PMD_SIZE; > > + /* > + * load_unaligned_zeropad() can lead to unwanted loads across page > + * boundaries. The unwanted loads are typically harmless. But, they > + * might be made to totally unrelated or even unmapped memory. > + * load_unaligned_zeropad() relies on exception fixup (#PF, #GP and now > + * #VE) to recover from these unwanted loads. > + * > + * But, this approach does not work for unaccepted memory. For TDX, a > + * load from unaccepted memory will not lead to a recoverable exception > + * within the guest. The guest will exit to the VMM where the only > + * recourse is to terminate the guest. > + * > + * There are three parts to fix this issue and comprehensively avoid > + * access to unaccepted memory. Together these ensure that an extra > + * “guard” page is accepted in addition to the memory that needs to be > + * used: > + * > + * 1. Implicitly extend the range_contains_unaccepted_memory(start, end) > + * checks up to end+2M if ‘end’ is aligned on a 2M boundary. > + * > + * 2. Implicitly extend accept_memory(start, end) to end+2M if ‘end’ is > + * aligned on a 2M boundary. Why do we need those unicode quotes and backticks in there? verify_diff: Warning: Unicode char [“] (0x8220 in line: + * “guard” page is accepted in addition to the memory that needs to be verify_diff: Warning: Unicode char [‘] (0x8216 in line: + * checks up to end+2M if ‘end’ is aligned on a 2M boundary. verify_diff: Warning: Unicode char [‘] (0x8216 in line: + * 2. Implicitly extend accept_memory(start, end) to end+2M if ‘end’ is verify_diff: Warning: Unicode char [‘] (0x8216 in line: + * needs to be done to make ‘page’ usable. That work might include verify_diff: Warning: Unicode char [‘] (0x8216 in line: + * accepting pages in addition to ‘page’ itself. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette