From patchwork Wed Sep 21 14:54:20 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ard Biesheuvel X-Patchwork-Id: 608050 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 0DAB3ECAAD8 for ; Wed, 21 Sep 2022 14:56:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230488AbiIUO4X (ORCPT ); Wed, 21 Sep 2022 10:56:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47432 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230368AbiIUOzr (ORCPT ); Wed, 21 Sep 2022 10:55:47 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7A23B3D5BB; Wed, 21 Sep 2022 07:55:05 -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 sin.source.kernel.org (Postfix) with ESMTPS id 85136CE1D97; Wed, 21 Sep 2022 14:55:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EE773C4314D; Wed, 21 Sep 2022 14:54:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1663772100; bh=wGMXGGR/LSLMUL86xmhmJr93fjH2ByIOKwd/q4PBA1k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Lhz8rM0rsHrh7/NDCcd/kSFYDLk5kzGIlx3MoI97OFyqptKYLFpd76rivLPgBu/3S HbGNy6R3j+ClPJskCwX4sK2/9HOSEJzwE8sEvmQx0rae/bT4REp5uAQTRuqhpJKEqB 7U/aYpMTvkcKLMAd9omVLbRZ7TleNUw4VKI8XhnFPuwK5KDpJuKPW8mFVc5twJYbfc thakF3BCyk43rHibvb0dLm2oT3OzDWeHYlG36BxFU0C2vF7wIyOowDHcVjQgt0JzLl OroaNy5V9vP5Lnub6+LEcNgPCEDqS4jzOJ++YZF+K6T8QqI7v3YBp26u0gZvHFMV2m bdSOPEreB54gw== From: Ard Biesheuvel To: linux-efi@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Ard Biesheuvel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Michael Roth Subject: [PATCH v2 14/16] x86/compressed: move startup32_check_sev_cbit() out of head_64.S Date: Wed, 21 Sep 2022 16:54:20 +0200 Message-Id: <20220921145422.437618-15-ardb@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220921145422.437618-1-ardb@kernel.org> References: <20220921145422.437618-1-ardb@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5275; i=ardb@kernel.org; h=from:subject; bh=wGMXGGR/LSLMUL86xmhmJr93fjH2ByIOKwd/q4PBA1k=; b=owEB7QES/pANAwAKAcNPIjmS2Y8kAcsmYgBjKyWaPY1SJA8qCJZi2MDi/OmCM8P0Cjs4fG4+n96x wJd0dW+JAbMEAAEKAB0WIQT72WJ8QGnJQhU3VynDTyI5ktmPJAUCYyslmgAKCRDDTyI5ktmPJAMvDA CvAKgw0ju+TsjnsYBAFzqoCLreVONbNkxrzKXwwSZwrkCOdOA/3j/3fECaKQaiwPIokeINsR7zcYQ4 Z53wbKrFZjQVcpzW3E9+ftmFpR4MkzpdLoSIq+lu9NYH7e1QfOxy0PxbeziKEC8LEOt9vQwDC1qxcn Lv9On4FQofAffNUjY6oVBlU+kKgbu1ldLUIM9xXjwLi6x52SzPuvLydM/rBVzAru/ih6VVrmw8WWaG ThudXRfIMkonMzw8HHbpZiC9v65apPa8HSdkncQj1Dl197ck0V850jYE4325jm05HKx/+3Gx0cpVNJ KfTP+K/kTct2RFzslr8xPIk7UcmbhQRbaDciqLaOwOUd3ge8Qq3XgEy0tVKcPlqmBaIprWsuTzzyF8 GvfwfMQoy1QGFmEFS4O1DVjyoOc/9A3a9Nk+50MsQTR+DRHSuSb/HeNBWW4fjtIhmh9yh/gwDoMgBb UUCKleTQmf1lOAqBMzGWvPBHs2u9uvxjaLqFrFZjlayPE= X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org Now that the startup32_check_sev_cbit() routine can execute from anywhere and behaves like an ordinary function, we no longer need to keep it in head_64.S. Signed-off-by: Ard Biesheuvel --- arch/x86/boot/compressed/head_64.S | 71 -------------------- arch/x86/boot/compressed/mem_encrypt.S | 68 +++++++++++++++++++ 2 files changed, 68 insertions(+), 71 deletions(-) diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index 639f688e4949..232cd3fa3e84 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -710,77 +710,6 @@ SYM_DATA_START(boot_idt) .endr SYM_DATA_END_LABEL(boot_idt, SYM_L_GLOBAL, boot_idt_end) -/* - * Check for the correct C-bit position when the startup_32 boot-path is used. - * - * The check makes use of the fact that all memory is encrypted when paging is - * disabled. The function creates 64 bits of random data using the RDRAND - * instruction. RDRAND is mandatory for SEV guests, so always available. If the - * hypervisor violates that the kernel will crash right here. - * - * The 64 bits of random data are stored to a memory location and at the same - * time kept in the %eax and %ebx registers. Since encryption is always active - * when paging is off the random data will be stored encrypted in main memory. - * - * Then paging is enabled. When the C-bit position is correct all memory is - * still mapped encrypted and comparing the register values with memory will - * succeed. An incorrect C-bit position will map all memory unencrypted, so that - * the compare will use the encrypted random data and fail. - */ -#ifdef CONFIG_AMD_MEM_ENCRYPT - .text -SYM_FUNC_START(startup32_check_sev_cbit) - pushl %ebx - pushl %ebp - - call 0f -0: popl %ebp - - /* Check for non-zero sev_status */ - movl (sev_status - 0b)(%ebp), %eax - testl %eax, %eax - jz 4f - - /* - * Get two 32-bit random values - Don't bail out if RDRAND fails - * because it is better to prevent forward progress if no random value - * can be gathered. - */ -1: rdrand %eax - jnc 1b -2: rdrand %ebx - jnc 2b - - /* Store to memory and keep it in the registers */ - leal (sev_check_data - 0b)(%ebp), %ebp - movl %eax, 0(%ebp) - movl %ebx, 4(%ebp) - - /* Enable paging to see if encryption is active */ - movl %cr0, %edx /* Backup %cr0 in %edx */ - movl $(X86_CR0_PG | X86_CR0_PE), %ecx /* Enable Paging and Protected mode */ - movl %ecx, %cr0 - - cmpl %eax, 0(%ebp) - jne 3f - cmpl %ebx, 4(%ebp) - jne 3f - - movl %edx, %cr0 /* Restore previous %cr0 */ - - jmp 4f - -3: /* Check failed - hlt the machine */ - hlt - jmp 3b - -4: - popl %ebp - popl %ebx - RET -SYM_FUNC_END(startup32_check_sev_cbit) -#endif - /* * Stack and heap for uncompression */ diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S index 6747e5e4c696..14cf04a1ed09 100644 --- a/arch/x86/boot/compressed/mem_encrypt.S +++ b/arch/x86/boot/compressed/mem_encrypt.S @@ -243,6 +243,74 @@ SYM_FUNC_START(startup32_load_idt) RET SYM_FUNC_END(startup32_load_idt) +/* + * Check for the correct C-bit position when the startup_32 boot-path is used. + * + * The check makes use of the fact that all memory is encrypted when paging is + * disabled. The function creates 64 bits of random data using the RDRAND + * instruction. RDRAND is mandatory for SEV guests, so always available. If the + * hypervisor violates that the kernel will crash right here. + * + * The 64 bits of random data are stored to a memory location and at the same + * time kept in the %eax and %ebx registers. Since encryption is always active + * when paging is off the random data will be stored encrypted in main memory. + * + * Then paging is enabled. When the C-bit position is correct all memory is + * still mapped encrypted and comparing the register values with memory will + * succeed. An incorrect C-bit position will map all memory unencrypted, so that + * the compare will use the encrypted random data and fail. + */ +SYM_FUNC_START(startup32_check_sev_cbit) + pushl %ebx + pushl %ebp + + call 0f +0: popl %ebp + + /* Check for non-zero sev_status */ + movl (sev_status - 0b)(%ebp), %eax + testl %eax, %eax + jz 4f + + /* + * Get two 32-bit random values - Don't bail out if RDRAND fails + * because it is better to prevent forward progress if no random value + * can be gathered. + */ +1: rdrand %eax + jnc 1b +2: rdrand %ebx + jnc 2b + + /* Store to memory and keep it in the registers */ + leal (sev_check_data - 0b)(%ebp), %ebp + movl %eax, 0(%ebp) + movl %ebx, 4(%ebp) + + /* Enable paging to see if encryption is active */ + movl %cr0, %edx /* Backup %cr0 in %edx */ + movl $(X86_CR0_PG | X86_CR0_PE), %ecx /* Enable Paging and Protected mode */ + movl %ecx, %cr0 + + cmpl %eax, 0(%ebp) + jne 3f + cmpl %ebx, 4(%ebp) + jne 3f + + movl %edx, %cr0 /* Restore previous %cr0 */ + + jmp 4f + +3: /* Check failed - hlt the machine */ + hlt + jmp 3b + +4: + popl %ebp + popl %ebx + RET +SYM_FUNC_END(startup32_check_sev_cbit) + .code64 #include "../../kernel/sev_verify_cbit.S"