Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions

Wei Huang
2021-01-12T21:52:11Z

On 1/12/21 6:15 AM, Vitaly Kuznetsov wrote:
> Wei Huang <wei.huang2@amd.com> writes:
>
>> From: Bandan Das <bsd@redhat.com>
>>
>> While running VM related instructions (VMRUN/VMSAVE/VMLOAD), some AMD
>> CPUs check EAX against reserved memory regions (e.g. SMM memory on host)
>> before checking VMCB's instruction intercept. If EAX falls into such
>> memory areas, #GP is triggered before VMEXIT. This causes problem under
>> nested virtualization. To solve this problem, KVM needs to trap #GP and
>> check the instructions triggering #GP. For VM execution instructions,
>> KVM emulates these instructions; otherwise it re-injects #GP back to
>> guest VMs.
>>
>> Signed-off-by: Bandan Das <bsd@redhat.com>
>> Co-developed-by: Wei Huang <wei.huang2@amd.com>
>> Signed-off-by: Wei Huang <wei.huang2@amd.com>
>> ---
>> arch/x86/include/asm/kvm_host.h | 8 +-
>> arch/x86/kvm/mmu.h | 1 +
>> arch/x86/kvm/mmu/mmu.c | 7 ++
>> arch/x86/kvm/svm/svm.c | 157 +++++++++++++++++++-------------
>> arch/x86/kvm/svm/svm.h | 8 ++
>> arch/x86/kvm/vmx/vmx.c | 2 +-
>> arch/x86/kvm/x86.c | 37 +++++++-
>> 7 files changed, 146 insertions(+), 74 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 3d6616f6f6ef..0ddc309f5a14 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -1450,10 +1450,12 @@ extern u64 kvm_mce_cap_supported;
>> * due to an intercepted #UD (see EMULTYPE_TRAP_UD).
>> * Used to test the full emulator from userspace.
>> *
>> - * EMULTYPE_VMWARE_GP - Set when emulating an intercepted #GP for VMware
>> + * EMULTYPE_PARAVIRT_GP - Set when emulating an intercepted #GP for VMware
>> * backdoor emulation, which is opt in via module param.
>> * VMware backoor emulation handles select instructions
>> - * and reinjects the #GP for all other cases.
>> + * and reinjects #GP for all other cases. This also
>> + * handles other cases where #GP condition needs to be
>> + * handled and emulated appropriately
>> *
>> * EMULTYPE_PF - Set when emulating MMIO by way of an intercepted #PF, in which
>> * case the CR2/GPA value pass on the stack is valid.
>> @@ -1463,7 +1465,7 @@ extern u64 kvm_mce_cap_supported;
>> #define EMULTYPE_SKIP (1 << 2)
>> #define EMULTYPE_ALLOW_RETRY_PF (1 << 3)
>> #define EMULTYPE_TRAP_UD_FORCED (1 << 4)
>> -#define EMULTYPE_VMWARE_GP (1 << 5)
>> +#define EMULTYPE_PARAVIRT_GP (1 << 5)
>> #define EMULTYPE_PF (1 << 6)
>>
>> int kvm_emulate_instruction(struct kvm_vcpu *vcpu, int emulation_type);
>> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
>> index 581925e476d6..1a2fff4e7140 100644
>> --- a/arch/x86/kvm/mmu.h
>> +++ b/arch/x86/kvm/mmu.h
>> @@ -219,5 +219,6 @@ int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);
>>
>> int kvm_mmu_post_init_vm(struct kvm *kvm);
>> void kvm_mmu_pre_destroy_vm(struct kvm *kvm);
>> +bool kvm_is_host_reserved_region(u64 gpa);
>
> Just a suggestion: "kvm_gpa_in_host_reserved()" maybe?

Will do in v2.

>
>>
>> #endif
>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>> index 6d16481aa29d..c5c4aaf01a1a 100644
>> --- a/arch/x86/kvm/mmu/mmu.c
>> +++ b/arch/x86/kvm/mmu/mmu.c
>> @@ -50,6 +50,7 @@
>> #include <asm/io.h>
>> #include <asm/vmx.h>
>> #include <asm/kvm_page_track.h>
>> +#include <asm/e820/api.h>
>> #include "trace.h"
>>
>> extern bool itlb_multihit_kvm_mitigation;
>> @@ -5675,6 +5676,12 @@ void kvm_mmu_slot_set_dirty(struct kvm *kvm,
>> }
>> EXPORT_SYMBOL_GPL(kvm_mmu_slot_set_dirty);
>>
>> +bool kvm_is_host_reserved_region(u64 gpa)
>> +{
>> + return e820__mbapped_raw_any(gpa-1, gpa+1, E820_TYPE_RESERVED);
>> +}
>
> While _e820__mapped_any()'s doc says '.. checks if any part of the
> range <start,end> is mapped ..' it seems to me that the real check is
> [start, end) so we should use 'gpa' instead of 'gpa-1', no?

I think you are right. The statement of "entry->addr >= end ||
entry->addr + entry->size <= start" shows the checking is against the
area of [start, end).

>
>> +EXPORT_SYMBOL_GPL(kvm_is_host_reserved_region);
>> +
>> void kvm_mmu_zap_all(struct kvm *kvm)
>> {
>> struct kvm_mmu_page *sp, *node;
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index 7ef171790d02..74620d32aa82 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -288,6 +288,7 @@ int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
>> if (!(efer & EFER_SVME)) {
>> svm_leave_nested(svm);
>> svm_set_gif(svm, true);
>> + clr_exception_intercept(svm, GP_VECTOR);
>>
>> /*
>> * Free the nested guest state, unless we are in SMM.
>> @@ -309,6 +310,10 @@ int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
>>
>> svm->vmcb->save.efer = efer | EFER_SVME;
>> vmcb_mark_dirty(svm->vmcb, VMCB_CR);
>> + /* Enable GP interception for SVM instructions if needed */
>> + if (efer & EFER_SVME)
>> + set_exception_intercept(svm, GP_VECTOR);
>> +
>> return 0;
>> }
>>
>> @@ -1957,22 +1962,104 @@ static int ac_interception(struct vcpu_svm *svm)
>> return 1;
>> }
>>
>> +static int vmload_interception(struct vcpu_svm *svm)
>> +{
>> + struct vmcb *nested_vmcb;
>> + struct kvm_host_map map;
>> + int ret;
>> +
>> + if (nested_svm_check_permissions(svm))
>> + return 1;
>> +
>> + ret = kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(svm->vmcb->save.rax), &map);
>> + if (ret) {
>> + if (ret == -EINVAL)
>> + kvm_inject_gp(&svm->vcpu, 0);
>> + return 1;
>> + }
>> +
>> + nested_vmcb = map.hva;
>> +
>> + ret = kvm_skip_emulated_instruction(&svm->vcpu);
>> +
>> + nested_svm_vmloadsave(nested_vmcb, svm->vmcb);
>> + kvm_vcpu_unmap(&svm->vcpu, &map, true);
>> +
>> + return ret;
>> +}
>> +
>> +static int vmsave_interception(struct vcpu_svm *svm)
>> +{
>> + struct vmcb *nested_vmcb;
>> + struct kvm_host_map map;
>> + int ret;
>> +
>> + if (nested_svm_check_permissions(svm))
>> + return 1;
>> +
>> + ret = kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(svm->vmcb->save.rax), &map);
>> + if (ret) {
>> + if (ret == -EINVAL)
>> + kvm_inject_gp(&svm->vcpu, 0);
>> + return 1;
>> + }
>> +
>> + nested_vmcb = map.hva;
>> +
>> + ret = kvm_skip_emulated_instruction(&svm->vcpu);
>> +
>> + nested_svm_vmloadsave(svm->vmcb, nested_vmcb);
>> + kvm_vcpu_unmap(&svm->vcpu, &map, true);
>> +
>> + return ret;
>> +}
>> +
>> +static int vmrun_interception(struct vcpu_svm *svm)
>> +{
>> + if (nested_svm_check_permissions(svm))
>> + return 1;
>> +
>> + return nested_svm_vmrun(svm);
>> +}
>> +
>> +/* Emulate SVM VM execution instructions */
>> +static int svm_emulate_vm_instr(struct kvm_vcpu *vcpu, u8 modrm)
>> +{
>> + struct vcpu_svm *svm = to_svm(vcpu);
>> +
>> + switch (modrm) {
>> + case 0xd8: /* VMRUN */
>> + return vmrun_interception(svm);
>> + case 0xda: /* VMLOAD */
>> + return vmload_interception(svm);
>> + case 0xdb: /* VMSAVE */
>> + return vmsave_interception(svm);
>> + default:
>> + /* inject a #GP for all other cases */
>> + kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
>> + return 1;
>> + }
>> +}
>> +
>> static int gp_interception(struct vcpu_svm *svm)
>> {
>> struct kvm_vcpu *vcpu = &svm->vcpu;
>> u32 error_code = svm->vmcb->control.exit_info_1;
>> -
>> - WARN_ON_ONCE(!enable_vmware_backdoor);
>> + int rc;
>>
>> /*
>> - * VMware backdoor emulation on #GP interception only handles IN{S},
>> - * OUT{S}, and RDPMC, none of which generate a non-zero error code.
>> + * Only VMware backdoor and SVM VME errata are handled. Neither of
>> + * them has non-zero error codes.
>> */
>> if (error_code) {
>> kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
>> return 1;
>> }
>> - return kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE_GP);
>> +
>> + rc = kvm_emulate_instruction(vcpu, EMULTYPE_PARAVIRT_GP);
>> + if (rc > 1)
>> + rc = svm_emulate_vm_instr(vcpu, rc);
>> + return rc;
>> }
>>
>> static bool is_erratum_383(void)
>> @@ -2113,66 +2200,6 @@ static int vmmcall_interception(struct vcpu_svm *svm)
>> return kvm_emulate_hypercall(&svm->vcpu);
>> }
>>
>> -static int vmload_interception(struct vcpu_svm *svm)
>> -{
>> - struct vmcb *nested_vmcb;
>> - struct kvm_host_map map;
>> - int ret;
>> -
>> - if (nested_svm_check_permissions(svm))
>> - return 1;
>> -
>> - ret = kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(svm->vmcb->save.rax), &map);
>> - if (ret) {
>> - if (ret == -EINVAL)
>> - kvm_inject_gp(&svm->vcpu, 0);
>> - return 1;
>> - }
>> -
>> - nested_vmcb = map.hva;
>> -
>> - ret = kvm_skip_emulated_instruction(&svm->vcpu);
>> -
>> - nested_svm_vmloadsave(nested_vmcb, svm->vmcb);
>> - kvm_vcpu_unmap(&svm->vcpu, &map, true);
>> -
>> - return ret;
>> -}
>> -
>> -static int vmsave_interception(struct vcpu_svm *svm)
>> -{
>> - struct vmcb *nested_vmcb;
>> - struct kvm_host_map map;
>> - int ret;
>> -
>> - if (nested_svm_check_permissions(svm))
>> - return 1;
>> -
>> - ret = kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(svm->vmcb->save.rax), &map);
>> - if (ret) {
>> - if (ret == -EINVAL)
>> - kvm_inject_gp(&svm->vcpu, 0);
>> - return 1;
>> - }
>> -
>> - nested_vmcb = map.hva;
>> -
>> - ret = kvm_skip_emulated_instruction(&svm->vcpu);
>> -
>> - nested_svm_vmloadsave(svm->vmcb, nested_vmcb);
>> - kvm_vcpu_unmap(&svm->vcpu, &map, true);
>> -
>> - return ret;
>> -}
>> -
>> -static int vmrun_interception(struct vcpu_svm *svm)
>> -{
>> - if (nested_svm_check_permissions(svm))
>> - return 1;
>> -
>> - return nested_svm_vmrun(svm);
>> -}
>> -
>
> Maybe if you'd do it the other way around and put gp_interception()
> after vm{load,save,run}_interception(), the diff (and code churn)
> would've been smaller?

Agreed.

>
>> void svm_set_gif(struct vcpu_svm *svm, bool value)
>> {
>> if (value) {
>> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
>> index 0fe874ae5498..d5dffcf59afa 100644
>> --- a/arch/x86/kvm/svm/svm.h
>> +++ b/arch/x86/kvm/svm/svm.h
>> @@ -350,6 +350,14 @@ static inline void clr_exception_intercept(struct vcpu_svm *svm, u32 bit)
>> recalc_intercepts(svm);
>> }
>>
>> +static inline bool is_exception_intercept(struct vcpu_svm *svm, u32 bit)
>> +{
>> + struct vmcb *vmcb = get_host_vmcb(svm);
>> +
>> + WARN_ON_ONCE(bit >= 32);
>> + return vmcb_is_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit);
>> +}
>> +
>> static inline void svm_set_intercept(struct vcpu_svm *svm, int bit)
>> {
>> struct vmcb *vmcb = get_host_vmcb(svm);
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index 2af05d3b0590..5fac2f7cba24 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -4774,7 +4774,7 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
>> kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
>> return 1;
>> }
>> - return kvm_emulate_instruction(vcpu, EMULTYPE_VMWARE_GP);
>> + return kvm_emulate_instruction(vcpu, EMULTYPE_PARAVIRT_GP);
>> }
>>
>> /*
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 9a8969a6dd06..c3662fc3b1bc 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -7014,7 +7014,7 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
>> ++vcpu->stat.insn_emulation_fail;
>> trace_kvm_emulate_insn_failed(vcpu);
>>
>> - if (emulation_type & EMULTYPE_VMWARE_GP) {
>> + if (emulation_type & EMULTYPE_PARAVIRT_GP) {
>> kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
>> return 1;
>> }
>> @@ -7267,6 +7267,28 @@ static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r)
>> return false;
>> }
>>
>> +static int is_vm_instr_opcode(struct x86_emulate_ctxt *ctxt)
>
> Nit: it seems we either return '0' or 'ctxt->modrm' which is 'u8', so
> 'u8' instead of 'int' maybe?

Agreed. Also Paolo has some comments around this area as well. We will
take these comments into consideration in v2.

>
>> +{
>> + unsigned long rax;
>> +
>> + if (ctxt->b != 0x1)
>> + return 0;
>> +
>> + switch (ctxt->modrm) {
>> + case 0xd8: /* VMRUN */
>> + case 0xda: /* VMLOAD */
>> + case 0xdb: /* VMSAVE */
>> + rax = kvm_register_read(emul_to_vcpu(ctxt), VCPU_REGS_RAX);
>> + if (!kvm_is_host_reserved_region(rax))
>> + return 0;
>> + break;
>> + default:
>> + return 0;
>> + }
>> +
>> + return ctxt->modrm;
>> +}
>> +
>> static bool is_vmware_backdoor_opcode(struct x86_emulate_ctxt *ctxt)
>> {
>> switch (ctxt->opcode_len) {
>> @@ -7305,6 +7327,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>> struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
>> bool writeback = true;
>> bool write_fault_to_spt;
>> + int vminstr;
>>
>> if (unlikely(!kvm_x86_ops.can_emulate_instruction(vcpu, insn, insn_len)))
>> return 1;
>> @@ -7367,10 +7390,14 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>> }
>> }
>>
>> - if ((emulation_type & EMULTYPE_VMWARE_GP) &&
>> - !is_vmware_backdoor_opcode(ctxt)) {
>> - kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
>> - return 1;
>> + if (emulation_type & EMULTYPE_PARAVIRT_GP) {
>> + vminstr = is_vm_instr_opcode(ctxt);
>> + if (!vminstr && !is_vmware_backdoor_opcode(ctxt)) {
>> + kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
>> + return 1;
>> + }
>> + if (vminstr)
>> + return vminstr;
>> }
>>
>> /*
>