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 9A6F0C77B72 for ; Thu, 20 Apr 2023 11:07:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234849AbjDTLHU (ORCPT ); Thu, 20 Apr 2023 07:07:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53952 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234711AbjDTLFS (ORCPT ); Thu, 20 Apr 2023 07:05:18 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B3C3AE7C; Thu, 20 Apr 2023 04:04:00 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id BA7DB647E4; Thu, 20 Apr 2023 11:03:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D0B5FC4339E; Thu, 20 Apr 2023 11:03:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1681988595; bh=XuH6j3tz7tJ5sPV1lAEwMCZ7xX0rapL3aIgBjKsrpKA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GXKVhGIkrEgT6WmMRIq3DW5rRHhXDS/vy6GXqsZJ+v80JaRQnwG6EP30YRfioJHUR G/domJg13ku1Rhaue+Ugt6QzdEpB0VC2zj8iCBC9y3OyRj8+LfckqcSSj/H5GTE9b8 kTdfVE0Qe+3ZUfRceHF3svykBVWJ9GNULWzj1a3mCo7j5QDfFtKdKerDrk+1FCKf36 2tIRINEFKW9Afy6KvYJE8CQv8bCEaiY9dvLAd8d/UEav88tocWio1meATlmhbybDDM fB9FwbZg+TOVgsjWhCDHCc8n33ASXRLrscDq6/26WqqwXDSLZAfj51dKH2SfzyLfTX IzsvNQFyVdirA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Michael Kelley , Wei Liu , Sasha Levin , kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, linux-hyperv@vger.kernel.org Subject: [PATCH AUTOSEL 5.15 3/7] x86/hyperv: Block root partition functionality in a Confidential VM Date: Thu, 20 Apr 2023 07:03:03 -0400 Message-Id: <20230420110308.506181-3-sashal@kernel.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230420110308.506181-1-sashal@kernel.org> References: <20230420110308.506181-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Michael Kelley [ Upstream commit f8acb24aaf89fc46cd953229462ea8abe31b395f ] Hyper-V should never specify a VM that is a Confidential VM and also running in the root partition. Nonetheless, explicitly block such a combination to guard against a compromised Hyper-V maliciously trying to exploit root partition functionality in a Confidential VM to expose Confidential VM secrets. No known bug is being fixed, but the attack surface for Confidential VMs on Hyper-V is reduced. Signed-off-by: Michael Kelley Link: https://lore.kernel.org/r/1678894453-95392-1-git-send-email-mikelley@microsoft.com Signed-off-by: Wei Liu Signed-off-by: Sasha Levin --- arch/x86/kernel/cpu/mshyperv.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index ba0efc30fac52..8d3c649a1769b 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -289,12 +289,16 @@ static void __init ms_hyperv_init_platform(void) * To mirror what Windows does we should extract CPU management * features and use the ReservedIdentityBit to detect if Linux is the * root partition. But that requires negotiating CPU management - * interface (a process to be finalized). + * interface (a process to be finalized). For now, use the privilege + * flag as the indicator for running as root. * - * For now, use the privilege flag as the indicator for running as - * root. + * Hyper-V should never specify running as root and as a Confidential + * VM. But to protect against a compromised/malicious Hyper-V trying + * to exploit root behavior to expose Confidential VM memory, ignore + * the root partition setting if also a Confidential VM. */ - if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_CPU_MANAGEMENT) { + if ((ms_hyperv.priv_high & HV_CPU_MANAGEMENT) && + !(ms_hyperv.priv_high & HV_ISOLATION)) { hv_root_partition = true; pr_info("Hyper-V: running as root partition\n"); } -- 2.39.2