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    Subject[PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions
    Date
    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);

    #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;
    }

    /*
    --
    2.27.0
    \
     
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