From patchwork Fri Jul 29 13:48:01 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michal Luczaj X-Patchwork-Id: 594401 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 1FB48C00144 for ; Fri, 29 Jul 2022 14:44:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235355AbiG2OoL (ORCPT ); Fri, 29 Jul 2022 10:44:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48760 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235283AbiG2OoL (ORCPT ); Fri, 29 Jul 2022 10:44:11 -0400 Received: from mailtransmit05.runbox.com (mailtransmit05.runbox.com [IPv6:2a0c:5a00:149::26]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C00957E025 for ; Fri, 29 Jul 2022 07:44:08 -0700 (PDT) Received: from mailtransmit02.runbox ([10.9.9.162] helo=aibo.runbox.com) by mailtransmit05.runbox.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1oHQNS-0045gm-Jb; Fri, 29 Jul 2022 15:50:06 +0200 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=rbox.co; s=selector1; h=Content-Transfer-Encoding:MIME-Version:Message-Id:Date:Subject :Cc:To:From; bh=I8JQffYkp7PTLavONuPZCV5xoA7eupc8ZymQ1b2jLBY=; b=SP1pYn+ArfMo7 3d/x00ET6pVDrTMoYFTwjQdyBFr056FSnaL0zK4SF9OSfvF6WjPSMrH7sysYqhh+qA8FZUp2IrSDr ml8tRAcjB0Q4xhRIe6VJXYodKSRIdtDc5TspAZkVyRfHVRikSecEfkn6GVBKGuwzKV/mr2F961ve4 XLlEk9fqP0Xt5927ROU04RKmUTnactKWtdsfpObeUOqtejO7vOOlU6RNJDD62MbiLpRSfoHJdeMs9 LVud9KZtrN36dlfkeDOw7Dy5Wz3hv+8Onw46xrqN+yJo3W50230DMke9rmAtAAYp1FerjmnSlqj17 FfHfo9lchffG6d2BDbcIQ==; Received: from [10.9.9.72] (helo=submission01.runbox) by mailtransmit02.runbox with esmtp (Exim 4.86_2) (envelope-from ) id 1oHQNS-0004Gc-3c; Fri, 29 Jul 2022 15:50:06 +0200 Received: by submission01.runbox with esmtpsa [Authenticated ID (604044)] (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) id 1oHQNI-0001bD-Ff; Fri, 29 Jul 2022 15:49:56 +0200 From: Michal Luczaj To: kvm@vger.kernel.org Cc: linux-kselftest@vger.kernel.org, seanjc@google.com, pbonzini@redhat.com, shuah@kernel.org, Michal Luczaj Subject: [PATCH 1/2] KVM: x86: emulator: Fix illegal LEA handling Date: Fri, 29 Jul 2022 15:48:01 +0200 Message-Id: <20220729134801.1120-1-mhal@rbox.co> X-Mailer: git-send-email 2.32.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org The emulator mishandles LEA with register source operand. Even though such LEA is illegal, it can be encoded and fed to CPU. In which case real hardware throws #UD. The emulator, instead, returns address of x86_emulate_ctxt._regs. This info leak hurts host's kASLR. Tell the decoder that illegal LEA is not to be emulated. Signed-off-by: Michal Luczaj Reviewed-by: Sean Christopherson --- What the emulator does for LEA is simply: case 0x8d: /* lea r16/r32, m */ ctxt->dst.val = ctxt->src.addr.mem.ea; break; And it makes sense if you assume that LEA's source operand is always memory. But because there is a race window between VM-exit and the decoder instruction fetch, emulator can be force fed an arbitrary opcode of choice. Including some that are simply illegal and would cause #UD in normal circumstances. Such as a LEA with a register-direct source operand -- for which the emulator sets `op->addr.reg`, but reads `op->addr.mem.ea`. union { unsigned long *reg; struct segmented_address { ulong ea; unsigned seg; } mem; ... } addr; Because `reg` and `mem` are in union, emulator reveals address in host's memory. I hope this patch is not considered an `instr_dual` abuse? arch/x86/kvm/emulate.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index f8382abe22ff..7c14706372d0 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4566,6 +4566,10 @@ static const struct mode_dual mode_dual_63 = { N, I(DstReg | SrcMem32 | ModRM | Mov, em_movsxd) }; +static const struct instr_dual instr_dual_8d = { + D(DstReg | SrcMem | ModRM | NoAccess), N +}; + static const struct opcode opcode_table[256] = { /* 0x00 - 0x07 */ F6ALU(Lock, em_add), @@ -4622,7 +4626,7 @@ static const struct opcode opcode_table[256] = { I2bv(DstMem | SrcReg | ModRM | Mov | PageTable, em_mov), I2bv(DstReg | SrcMem | ModRM | Mov, em_mov), I(DstMem | SrcNone | ModRM | Mov | PageTable, em_mov_rm_sreg), - D(ModRM | SrcMem | NoAccess | DstReg), + ID(0, &instr_dual_8d), I(ImplicitOps | SrcMem16 | ModRM, em_mov_sreg_rm), G(0, group1A), /* 0x90 - 0x97 */