From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 77CC251804 for ; Thu, 1 Jun 2023 18:26:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1685643975; x=1717179975; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=aHz7WO7wShdd679ArCfVvIALDE990d9+23AGlVsKS9M=; b=TD0TwTnc5yTxicNZHYWxae7OEmJ/Gbl2DHYawXYrhRiXCh/Pu1OXoNek 2Gm0efhqKU8OWKa9J8KGu6YbHQIoo7RtA+CZMhQuGYt+xeJRllxvEQuqc bG6iatEY1prWeEcy4YaubUIsCpKRO6QKcrSXyJrNWTO4mnTgEw43Os65s J5BM0egnBXVV2eFCV7qy6K4Tjf1pGIbvFF00A/6oDyUBWWzzLfHewwumM 1yVnR7S8RgWvdppqXPJpDelASb69Na07c9xGBzABO5l+gW5bDLYVQoFe2 tunJos2dc6BbFNslDejgPaOMit516V89r1NpB2EJolc4k9/5CVqtD8D8d g==; X-IronPort-AV: E=McAfee;i="6600,9927,10728"; a="383920607" X-IronPort-AV: E=Sophos;i="6.00,210,1681196400"; d="scan'208";a="383920607" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Jun 2023 11:26:12 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10728"; a="772539957" X-IronPort-AV: E=Sophos;i="6.00,210,1681196400"; d="scan'208";a="772539957" Received: from fmaislin-mobl1.ger.corp.intel.com (HELO box.shutemov.name) ([10.252.47.213]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Jun 2023 11:26:04 -0700 Received: by box.shutemov.name (Postfix, from userid 1000) id 8C4C910B6AD; Thu, 1 Jun 2023 21:25:52 +0300 (+03) From: "Kirill A. Shutemov" To: Borislav Petkov , Andy Lutomirski , Dave Hansen , 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 , Dario Faggioli , Mike Rapoport , David Hildenbrand , Mel Gorman , marcelo.cerri@canonical.com, tim.gardner@canonical.com, khalid.elmously@canonical.com, philip.cox@canonical.com, aarcange@redhat.com, peterx@redhat.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" , Dave Hansen Subject: [PATCHv13 6/9] efi/unaccepted: Avoid load_unaligned_zeropad() stepping into unaccepted memory Date: Thu, 1 Jun 2023 21:25:40 +0300 Message-Id: <20230601182543.19036-7-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20230601182543.19036-1-kirill.shutemov@linux.intel.com> References: <20230601182543.19036-1-kirill.shutemov@linux.intel.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 two 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+unit_size if 'end' is aligned on a unit_size boundary. 2. Implicitly extend accept_memory(start, end) to end+unit_size if 'end' is aligned on a unit_size boundary. 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 be on unaccepted_pages list This 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 Reviewed-by: Dave Hansen Reviewed-by: Ard Biesheuvel Reviewed-by: Tom Lendacky --- drivers/firmware/efi/unaccepted_memory.c | 35 ++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/drivers/firmware/efi/unaccepted_memory.c b/drivers/firmware/efi/unaccepted_memory.c index bb91c41f76fb..3d1ca60916dd 100644 --- a/drivers/firmware/efi/unaccepted_memory.c +++ b/drivers/firmware/efi/unaccepted_memory.c @@ -37,6 +37,34 @@ void accept_memory(phys_addr_t start, phys_addr_t end) start -= unaccepted->phys_base; end -= unaccepted->phys_base; + /* + * 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 two 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+unit_size if 'end' is aligned on a unit_size + * boundary. + * + * 2. Implicitly extend accept_memory(start, end) to end+unit_size if + * 'end' is aligned on a unit_size boundary. (immediately following + * this comment) + */ + if (!(end % unit_size)) + end += unit_size; + /* Make sure not to overrun the bitmap */ if (end > unaccepted->size * unit_size * BITS_PER_BYTE) end = unaccepted->size * unit_size * BITS_PER_BYTE; @@ -84,6 +112,13 @@ bool range_contains_unaccepted_memory(phys_addr_t start, phys_addr_t end) start -= unaccepted->phys_base; end -= unaccepted->phys_base; + /* + * Also consider the unaccepted state of the *next* page. See fix #1 in + * the comment on load_unaligned_zeropad() in accept_memory(). + */ + if (!(end % unit_size)) + end += unit_size; + /* Make sure not to overrun the bitmap */ if (end > unaccepted->size * unit_size * BITS_PER_BYTE) end = unaccepted->size * unit_size * BITS_PER_BYTE; -- 2.39.3