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    SubjectRe: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions
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    On Tue, 2021-01-12 at 00:37 -0600, Wei Huang wrote:
    > 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>

    This is the ultimate fix for this bug that I had in mind,
    but I didn't dare to develop it, thinking it won't be accepted
    due to the added complexity.

    From a cursory look this look all right, and I will review
    and test this either today or tomorrow.

    Thank you very much for doing the right fix for this bug.

    Best regards,
    Maxim Levitsky

    > ---
    > 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);
    >
    > #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__mapped_raw_any(gpa-1, gpa+1, E820_TYPE_RESERVED);
    > +}
    > +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);
    > -}
    > -
    > 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)
    > +{
    > + 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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