Messages in this thread |  | | From | Wanpeng Li <> | Subject | [PATCH v5 0/2] KVM: X86: Add Force Emulation Prefix for "emulate the next instruction" | Date | Tue, 3 Apr 2018 16:28:47 -0700 |
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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 <stdio.h> #include <string.h>
#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"); }
v3 -> v4: * forwarding emulation failure to userspace v2 -> v3: * fix compile warning v1 -> v2: * update patch descriptions * move handle_ud to x86.c, shared by vmx and svm * the parameter is in kvm module * rename parameter to force_emulation_prefix
Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Andrew Cooper <andrew.cooper3@citrix.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Liran Alon <liran.alon@oracle.com>
Wanpeng Li (2): KVM: X86: Introduce handle_ud() KVM: X86: Add Force Emulation Prefix for "emulate the next instruction"
arch/x86/kvm/svm.c | 9 +-------- arch/x86/kvm/vmx.c | 10 ++-------- arch/x86/kvm/x86.c | 31 +++++++++++++++++++++++++++++++ arch/x86/kvm/x86.h | 2 ++ 4 files changed, 36 insertions(+), 16 deletions(-)
-- 2.7.4
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