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Date:   Tue, 12 Jan 2021 15:50:48 -0600
From:   Wei Huang <wei.huang2@....com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        seanjc@...gle.com, joro@...tes.org, bp@...en8.de,
        tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        jmattson@...gle.com, wanpengli@...cent.com, bsd@...hat.com,
        dgilbert@...hat.com, mlevitsk@...hat.com
Subject: Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by
 VM instructions



On 1/12/21 6:15 AM, Vitaly Kuznetsov wrote:
> Wei Huang <wei.huang2@....com> writes:
> 
>> From: Bandan Das <bsd@...hat.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@...hat.com>
>> Co-developed-by: Wei Huang <wei.huang2@....com>
>> Signed-off-by: Wei Huang <wei.huang2@....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;
>>   	}
>>   
>>   	/*
> 

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