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");
}
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 <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Andrew Cooper <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Liran Alon <[email protected]>
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 | 29 +++++++++++++++++++++++++++++
arch/x86/kvm/x86.h | 2 ++
4 files changed, 34 insertions(+), 16 deletions(-)
--
2.7.4
From: Wanpeng Li <[email protected]>
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");
}
Suggested-by: Andrew Cooper <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Andrew Cooper <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Liran Alon <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/x86.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e3a60ab..40e2f78 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);
+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 {
@@ -4843,8 +4846,21 @@ EXPORT_SYMBOL_GPL(kvm_write_guest_virt_system);
int handle_ud(struct kvm_vcpu *vcpu)
{
enum emulation_result er;
+ int emulation_type = EMULTYPE_TRAP_UD;
+
+ 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) {
+ emulation_type = 0;
+ kvm_rip_write(vcpu, kvm_rip_read(vcpu) + sizeof(sig));
+ }
+ }
- er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD);
+ er = emulate_instruction(vcpu, emulation_type);
if (er == EMULATE_USER_EXIT)
return 0;
if (er != EMULATE_DONE)
--
2.7.4
From: Wanpeng Li <[email protected]>
Introduce handle_ud() to handle invalid opcode, this function will be
used by later patches.
Reviewed-by: Konrad Rzeszutek Wilk <[email protected]>
Reviewed-by: Liran Alon <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Andrew Cooper <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Liran Alon <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
arch/x86/kvm/svm.c | 9 +--------
arch/x86/kvm/vmx.c | 10 ++--------
arch/x86/kvm/x86.c | 13 +++++++++++++
arch/x86/kvm/x86.h | 2 ++
4 files changed, 18 insertions(+), 16 deletions(-)
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index cb46e98..65eb3b9 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2581,14 +2581,7 @@ static int bp_interception(struct vcpu_svm *svm)
static int ud_interception(struct vcpu_svm *svm)
{
- int er;
-
- er = emulate_instruction(&svm->vcpu, EMULTYPE_TRAP_UD);
- if (er == EMULATE_USER_EXIT)
- return 0;
- if (er != EMULATE_DONE)
- kvm_queue_exception(&svm->vcpu, UD_VECTOR);
- return 1;
+ return handle_ud(&svm->vcpu);
}
static int ac_interception(struct vcpu_svm *svm)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9bc05f5..63b46db 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6233,14 +6233,8 @@ static int handle_exception(struct kvm_vcpu *vcpu)
if (is_nmi(intr_info))
return 1; /* already handled by vmx_vcpu_run() */
- if (is_invalid_opcode(intr_info)) {
- er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD);
- if (er == EMULATE_USER_EXIT)
- return 0;
- if (er != EMULATE_DONE)
- kvm_queue_exception(vcpu, UD_VECTOR);
- return 1;
- }
+ if (is_invalid_opcode(intr_info))
+ return handle_ud(vcpu);
error_code = 0;
if (intr_info & INTR_INFO_DELIVER_CODE_MASK)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1583bdc..e3a60ab 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4840,6 +4840,19 @@ int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
}
EXPORT_SYMBOL_GPL(kvm_write_guest_virt_system);
+int handle_ud(struct kvm_vcpu *vcpu)
+{
+ enum emulation_result er;
+
+ er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD);
+ if (er == EMULATE_USER_EXIT)
+ return 0;
+ if (er != EMULATE_DONE)
+ kvm_queue_exception(vcpu, UD_VECTOR);
+ return 1;
+}
+EXPORT_SYMBOL_GPL(handle_ud);
+
static int vcpu_is_mmio_gpa(struct kvm_vcpu *vcpu, unsigned long gva,
gpa_t gpa, bool write)
{
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index b620cfa..b2f6191 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -219,6 +219,8 @@ int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
gva_t addr, void *val, unsigned int bytes,
struct x86_exception *exception);
+int handle_ud(struct kvm_vcpu *vcpu);
+
void kvm_vcpu_mtrr_init(struct kvm_vcpu *vcpu);
u8 kvm_mtrr_get_guest_memory_type(struct kvm_vcpu *vcpu, gfn_t gfn);
bool kvm_mtrr_valid(struct kvm_vcpu *vcpu, u32 msr, u64 data);
--
2.7.4
Hi Wanpeng,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on kvm/linux-next]
[also build test WARNING on next-20180327]
[cannot apply to v4.16-rc7]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Wanpeng-Li/KVM-X86-Add-Force-Emulation-Prefix-for-emulate-the-next-instruction/20180328-025804
base: https://git.kernel.org/pub/scm/virt/kvm/kvm.git linux-next
reproduce:
# apt-get install sparse
make ARCH=x86_64 allmodconfig
make C=1 CF=-D__CHECK_ENDIAN__
sparse warnings: (new ones prefixed by >>)
>> arch/x86/kvm/x86.c:149:20: sparse: symbol 'force_emulation_prefix' was not declared. Should it be static?
arch/x86/kvm/x86.c:2196:38: sparse: incorrect type in argument 1 (different address spaces) @@ expected void const [noderef] <asn:1>*<noident> @@ got d const [noderef] <asn:1>*<noident> @@
arch/x86/kvm/x86.c:2196:38: expected void const [noderef] <asn:1>*<noident>
arch/x86/kvm/x86.c:2196:38: got unsigned char [usertype] *
arch/x86/kvm/x86.c:7911:5: sparse: symbol 'kvm_valid_sregs' was not declared. Should it be static?
arch/x86/kvm/x86.c:8786:16: sparse: incompatible types in comparison expression (different address spaces)
arch/x86/include/asm/paravirt.h:783:9: sparse: context imbalance in 'vcpu_enter_guest' - unexpected unlock
Please review and possibly fold the followup patch.
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
Fixes: 9e028a15a849 ("KVM: X86: Add Force Emulation Prefix for "emulate the next instruction"")
Signed-off-by: Fengguang Wu <[email protected]>
---
x86.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 17bb968..44f1e72 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -146,7 +146,7 @@ bool __read_mostly enable_vmware_backdoor = false;
module_param(enable_vmware_backdoor, bool, S_IRUGO);
EXPORT_SYMBOL_GPL(enable_vmware_backdoor);
-bool __read_mostly force_emulation_prefix = false;
+static bool __read_mostly force_emulation_prefix = false;
module_param(force_emulation_prefix, bool, S_IRUGO);
#define KVM_NR_SHARED_MSRS 16
2018-03-28 5:15 GMT+08:00 kbuild test robot <[email protected]>:
> Hi Wanpeng,
>
> Thank you for the patch! Perhaps something to improve:
>
> [auto build test WARNING on kvm/linux-next]
> [also build test WARNING on next-20180327]
> [cannot apply to v4.16-rc7]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>
> url: https://github.com/0day-ci/linux/commits/Wanpeng-Li/KVM-X86-Add-Force-Emulation-Prefix-for-emulate-the-next-instruction/20180328-025804
> base: https://git.kernel.org/pub/scm/virt/kvm/kvm.git linux-next
> reproduce:
> # apt-get install sparse
> make ARCH=x86_64 allmodconfig
> make C=1 CF=-D__CHECK_ENDIAN__
>
>
> sparse warnings: (new ones prefixed by >>)
>
>>> arch/x86/kvm/x86.c:149:20: sparse: symbol 'force_emulation_prefix' was not declared. Should it be static?
> arch/x86/kvm/x86.c:2196:38: sparse: incorrect type in argument 1 (different address spaces) @@ expected void const [noderef] <asn:1>*<noident> @@ got d const [noderef] <asn:1>*<noident> @@
> arch/x86/kvm/x86.c:2196:38: expected void const [noderef] <asn:1>*<noident>
> arch/x86/kvm/x86.c:2196:38: got unsigned char [usertype] *
> arch/x86/kvm/x86.c:7911:5: sparse: symbol 'kvm_valid_sregs' was not declared. Should it be static?
> arch/x86/kvm/x86.c:8786:16: sparse: incompatible types in comparison expression (different address spaces)
> arch/x86/include/asm/paravirt.h:783:9: sparse: context imbalance in 'vcpu_enter_guest' - unexpected unlock
>
> Please review and possibly fold the followup patch.
Thanks for the report, I will fix it in the next version.
Regards,
Wanpeng Li