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

Vitaly Kuznetsov
2021-01-12T12:17:08Z

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?

>
> #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?

> +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?

> 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?

> +{
> + 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;
> }
>
> /*

--
Vitaly