From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752125AbeC3JJM (ORCPT ); Fri, 30 Mar 2018 05:09:12 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:42742 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750790AbeC3JHm (ORCPT ); Fri, 30 Mar 2018 05:07:42 -0400 X-Google-Smtp-Source: AIpwx49etu5qBp6iXnO0HmaS4T4g1Sjmbk/ey5k9onOl0YMGgAY37eBFHZufUQ0LChur2x8gnK0hQg== From: Wanpeng Li X-Google-Original-From: Wanpeng Li To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , Andrew Cooper , Konrad Rzeszutek Wilk , Liran Alon Subject: [PATCH v4 2/2] KVM: X86: Add Force Emulation Prefix for "emulate the next instruction" Date: Fri, 30 Mar 2018 02:06:44 -0700 Message-Id: <1522400804-4578-3-git-send-email-wanpengli@tencent.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1522400804-4578-1-git-send-email-wanpengli@tencent.com> References: <1522400804-4578-1-git-send-email-wanpengli@tencent.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wanpeng Li There is no easy way to force KVM to run an instruction through the emulator (by design as that will expose the x86 emulator as a significant attack-surface). However, we do wish to expose the x86 emulator in case we are testing it (e.g. via kvm-unit-tests). Therefore, this patch adds a "force emulation prefix" that is designed to raise #UD which KVM will trap and it's #UD exit-handler will match "force emulation prefix" to run instruction after prefix by the x86 emulator. To not expose the x86 emulator by default, we add a module parameter that should be off by default. A simple testcase here: #include #include #define HYPERVISOR_INFO 0x40000000 #define CPUID(idx, eax, ebx, ecx, edx) \ asm volatile (\ "ud2a; .ascii \"kvm\"; cpuid" \ :"=b" (*ebx), "=a" (*eax), "=c" (*ecx), "=d" (*edx) \ :"0"(idx) ); void main() { unsigned int eax, ebx, ecx, edx; char string[13]; CPUID(HYPERVISOR_INFO, &eax, &ebx, &ecx, &edx); *(unsigned int *)(string + 0) = ebx; *(unsigned int *)(string + 4) = ecx; *(unsigned int *)(string + 8) = edx; string[12] = 0; if (strncmp(string, "KVMKVMKVM\0\0\0", 12) == 0) printf("kvm guest\n"); else printf("bare hardware\n"); } Suggested-by: Andrew Cooper Reviewed-By: Liran Alon Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Andrew Cooper Cc: Konrad Rzeszutek Wilk Cc: Liran Alon Signed-off-by: Wanpeng Li --- arch/x86/kvm/x86.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1eb495e..c619564 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -146,6 +146,9 @@ bool __read_mostly enable_vmware_backdoor = false; module_param(enable_vmware_backdoor, bool, S_IRUGO); EXPORT_SYMBOL_GPL(enable_vmware_backdoor); +static bool __read_mostly force_emulation_prefix = false; +module_param(force_emulation_prefix, bool, S_IRUGO); + #define KVM_NR_SHARED_MSRS 16 struct kvm_shared_msrs_global { @@ -4844,6 +4847,18 @@ int handle_ud(struct kvm_vcpu *vcpu) { enum emulation_result er; + if (force_emulation_prefix) { + char sig[5]; /* ud2; .ascii "kvm" */ + struct x86_exception e; + + kvm_read_guest_virt(&vcpu->arch.emulate_ctxt, + kvm_get_linear_rip(vcpu), sig, sizeof(sig), &e); + if (memcmp(sig, "\xf\xbkvm", sizeof(sig)) == 0) { + kvm_rip_write(vcpu, kvm_rip_read(vcpu) + sizeof(sig)); + return emulate_instruction(vcpu, 0) == EMULATE_DONE; + } + } + er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD); if (er == EMULATE_USER_EXIT) return 0; -- 2.7.4