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=-12.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 3E570C55179 for ; Thu, 29 Oct 2020 02:12:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 07F7020720 for ; Thu, 29 Oct 2020 02:12:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388227AbgJ2CM3 (ORCPT ); Wed, 28 Oct 2020 22:12:29 -0400 Received: from 8bytes.org ([81.169.241.247]:36964 "EHLO theia.8bytes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726811AbgJ1VgZ (ORCPT ); Wed, 28 Oct 2020 17:36:25 -0400 Received: from cap.home.8bytes.org (p5b006b35.dip0.t-ipconnect.de [91.0.107.53]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)) (No client certificate requested) by theia.8bytes.org (Postfix) with ESMTPSA id A76184CA; Wed, 28 Oct 2020 17:47:06 +0100 (CET) From: Joerg Roedel To: x86@kernel.org Cc: Joerg Roedel , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Kees Cook , Arvind Sankar , Martin Radev , Tom Lendacky , linux-kernel@vger.kernel.org Subject: [PATCH v4 4/5] x86/head/64: Check SEV encryption before switching to kernel page-table Date: Wed, 28 Oct 2020 17:46:58 +0100 Message-Id: <20201028164659.27002-5-joro@8bytes.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20201028164659.27002-1-joro@8bytes.org> References: <20201028164659.27002-1-joro@8bytes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Joerg Roedel When SEV is enabled the kernel requests the C-Bit position again from the hypervisor to built its own page-table. Since the hypervisor is an untrusted source the C-bit position needs to be verified before the kernel page-table is used. Call the sev_verify_cbit() function before writing the CR3. Signed-off-by: Joerg Roedel --- arch/x86/kernel/head_64.S | 16 ++++++++++++++++ arch/x86/mm/mem_encrypt.c | 1 + 2 files changed, 17 insertions(+) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 7eb2a1c87969..3c417734790f 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -161,6 +161,21 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) /* Setup early boot stage 4-/5-level pagetables. */ addq phys_base(%rip), %rax + + /* + * For SEV guests: Verify that the C-bit is correct. A malicious + * hypervisor could lie about the C-bit position to perform a ROP + * attack on the guest by writing to the unencrypted stack and wait for + * the next RET instruction. + * %rsi carries pointer to realmode data and is callee-clobbered. Save + * and restore it. + */ + pushq %rsi + movq %rax, %rdi + call sev_verify_cbit + popq %rsi + + /* Switch to new page-table */ movq %rax, %cr3 /* Ensure I am executing from virtual addresses */ @@ -279,6 +294,7 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) SYM_CODE_END(secondary_startup_64) #include "verify_cpu.S" +#include "sev_verify_cbit.S" #ifdef CONFIG_HOTPLUG_CPU /* diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c index efbb3de472df..bc0833713be9 100644 --- a/arch/x86/mm/mem_encrypt.c +++ b/arch/x86/mm/mem_encrypt.c @@ -39,6 +39,7 @@ */ u64 sme_me_mask __section(".data") = 0; u64 sev_status __section(".data") = 0; +u64 sev_check_data __section(".data") = 0; EXPORT_SYMBOL(sme_me_mask); DEFINE_STATIC_KEY_FALSE(sev_enable_key); EXPORT_SYMBOL_GPL(sev_enable_key); -- 2.28.0