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 004C9C433F5 for ; Tue, 17 May 2022 15:35:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349935AbiEQPfn (ORCPT ); Tue, 17 May 2022 11:35:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36508 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350185AbiEQPfH (ORCPT ); Tue, 17 May 2022 11:35:07 -0400 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 320BF4F9E1; Tue, 17 May 2022 08:35:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1652801706; x=1684337706; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=fZtxSqO4KIAh0ipO8K6wy8wKDprGI920JXd4BfH9/jE=; b=NzISyU43lkVJSQxsKDicFgVaDysEqMw4Yl/mCdZr6HDwVcVWdzltkMKV J7AQ0+W8VR7wXV0MK0NCrjr8i+zl1+zoGeLkFT42khnmDdyJVFWEM/cF+ dlCxwR0YOstoylAFePNyFFmCCgqQEcXTuWka/mS1uso5A6oKIzWEw3G5m oZ+AFys80dHI5MfuqASsWpgx9AcPp3PUfqiZcXwwETDkQVCWcoR2U5xAS /HC2Y/RQXBKwFWvfhlduDHkBMElwPBip40YBJha5A0mmNhWgfZnVlcQVC wnHkWbWUzdmuizTX2QG/joVAEDS6CwQkLUmT5p4vJP9Os/CGO0kmeHCWN g==; X-IronPort-AV: E=McAfee;i="6400,9594,10350"; a="258783173" X-IronPort-AV: E=Sophos;i="5.91,233,1647327600"; d="scan'208";a="258783173" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 May 2022 08:35:05 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.91,233,1647327600"; d="scan'208";a="605408170" Received: from black.fi.intel.com ([10.237.72.28]) by orsmga001.jf.intel.com with ESMTP; 17 May 2022 08:34:58 -0700 Received: by black.fi.intel.com (Postfix, from userid 1000) id AE7C5B80; Tue, 17 May 2022 18:34:50 +0300 (EEST) From: "Kirill A. Shutemov" To: Borislav Petkov , Andy Lutomirski , Sean Christopherson , Andrew Morton , Joerg Roedel , Ard Biesheuvel Cc: 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, "Kirill A. Shutemov" Subject: [PATCHv6 09/15] x86/mm: Avoid load_unaligned_zeropad() stepping into unaccepted memory Date: Tue, 17 May 2022 18:34:38 +0300 Message-Id: <20220517153444.11195-10-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220517153444.11195-1-kirill.shutemov@linux.intel.com> References: <20220517153444.11195-1-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 memory_is_unaccepted(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. 3. Set PageUnaccepted() on both memory that itself needs to be accepted *and* memory where the next page needs to be accepted. Essentially, make PageUnaccepted(page) a marker for whether work needs to be done to make ‘page’ usable. That work might include accepting pages in addition to ‘page’ itself. Side note: This leads to something strange. Pages which were accepted at boot, marked by the firmware as accepted and will never _need_ to be accepted might have PageUnaccepted() set on them. PageUnaccepted(page) is a cue to ensure that the next page is accepted before ‘page’ can be used. This is an actual, real-world problem which was discovered during TDX testing. Signed-off-by: Kirill A. Shutemov --- arch/x86/mm/unaccepted_memory.c | 36 +++++++++++++++++++++++++ drivers/firmware/efi/libstub/x86-stub.c | 7 +++++ 2 files changed, 43 insertions(+) diff --git a/arch/x86/mm/unaccepted_memory.c b/arch/x86/mm/unaccepted_memory.c index 0a86380b2478..33bf70592a46 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. + * + * 3. Set PageUnaccepted() on both memory that itself needs to be + * accepted *and* memory where the next page needs to be accepted. + * Essentially, make PageUnaccepted(page) a marker for whether work + * needs to be done to make ‘page’ usable. That work might include + * accepting pages in addition to ‘page’ itself. + */ + if (!(end % PMD_SIZE)) + end += PMD_SIZE; + spin_lock_irqsave(&unaccepted_memory_lock, flags); for_each_set_bitrange_from(range_start, range_end, bitmap, DIV_ROUND_UP(end, PMD_SIZE)) { @@ -41,6 +73,10 @@ bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end) unsigned long flags; bool ret = false; + /* See comment on load_unaligned_zeropad() in accept_memory() */ + if (!(end % PMD_SIZE)) + end += PMD_SIZE; + spin_lock_irqsave(&unaccepted_memory_lock, flags); while (start < end) { if (test_bit(start / PMD_SIZE, bitmap)) { diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c index ec14a9a6436b..89705ae69cbf 100644 --- a/drivers/firmware/efi/libstub/x86-stub.c +++ b/drivers/firmware/efi/libstub/x86-stub.c @@ -606,6 +606,13 @@ static efi_status_t allocate_unaccepted_memory(struct boot_params *params, return EFI_SUCCESS; } + /* + * range_contains_unaccepted_memory() may need to check one 2M chunk + * beyond the end of RAM to deal with load_unaligned_zeropad(). Make + * sure that the bitmap is large enough handle it. + */ + max_addr += PMD_SIZE; + /* * If unaccepted memory is present allocate a bitmap to track what * memory has to be accepted before access. -- 2.35.1