[PATCH 05/10] KVM: allow compiling out SMM support

Paolo Bonzini
2022-10-27T16:50:42Z

Some users of KVM implement the UEFI variable store through a paravirtual device
that does not require the "SMM lockbox" component of edk2; allow them to
compile out system management mode, which is not a full implementation
especially in how it interacts with nested virtualization.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220929172016.319443-6-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/Kconfig | 11 ++++++++++
arch/x86/kvm/Makefile | 2 +-
arch/x86/kvm/smm.h | 12 ++++++++++
arch/x86/kvm/svm/svm.c | 2 ++
arch/x86/kvm/vmx/vmx.c | 2 ++
arch/x86/kvm/x86.c | 22 +++++++++++++++++--
tools/testing/selftests/kvm/x86_64/smm_test.c | 2 ++
7 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 67be7f217e37..fbeaa9ddef59 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -118,6 +118,17 @@ config KVM_AMD_SEV
Provides support for launching Encrypted VMs (SEV) and Encrypted VMs
with Encrypted State (SEV-ES) on AMD processors.

+config KVM_SMM
+ bool "System Management Mode emulation"
+ default y
+ depends on KVM
+ help
+ Provides support for KVM to emulate System Management Mode (SMM)
+ in virtual machines. This can be used by the virtual machine
+ firmware to implement UEFI secure boot.
+
+ If unsure, say Y.
+
config KVM_XEN
bool "Support for Xen hypercall interface"
depends on KVM
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index ec6f7656254b..6cf40f668277 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -20,7 +20,7 @@ endif

kvm-$(CONFIG_X86_64) += mmu/tdp_iter.o mmu/tdp_mmu.o
kvm-$(CONFIG_KVM_XEN) += xen.o
-kvm-y += smm.o
+kvm-$(CONFIG_KVM_SMM) += smm.o

kvm-intel-y += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
vmx/evmcs.o vmx/nested.o vmx/posted_intr.o
diff --git a/arch/x86/kvm/smm.h b/arch/x86/kvm/smm.h
index b0602a92e511..0e1bd8bd6dc4 100644
--- a/arch/x86/kvm/smm.h
+++ b/arch/x86/kvm/smm.h
@@ -8,6 +8,7 @@
#define PUT_SMSTATE(type, buf, offset, val) \
*(type *)((buf) + (offset) - 0x7e00) = val

+#ifdef CONFIG_KVM_SMM
static inline int kvm_inject_smi(struct kvm_vcpu *vcpu)
{
kvm_make_request(KVM_REQ_SMI, vcpu);
@@ -23,5 +24,16 @@ void kvm_smm_changed(struct kvm_vcpu *vcpu, bool in_smm);
void enter_smm(struct kvm_vcpu *vcpu);
int emulator_leave_smm(struct x86_emulate_ctxt *ctxt);
void process_smi(struct kvm_vcpu *vcpu);
+#else
+static inline int kvm_inject_smi(struct kvm_vcpu *vcpu) { return -ENOTTY; }
+static inline bool is_smm(struct kvm_vcpu *vcpu) { return false; }
+static inline void enter_smm(struct kvm_vcpu *vcpu) { WARN_ON_ONCE(1); }
+static inline void process_smi(struct kvm_vcpu *vcpu) { WARN_ON_ONCE(1); }
+
+/*
+ * emulator_leave_smm is used as a function pointer, so the
+ * stub is defined in x86.c.
+ */
+#endif

#endif
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 496ee7d1ae2f..6f7ceb35d2ff 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4150,6 +4150,8 @@ static bool svm_has_emulated_msr(struct kvm *kvm, u32 index)
case MSR_IA32_VMX_BASIC ... MSR_IA32_VMX_VMFUNC:
return false;
case MSR_IA32_SMBASE:
+ if (!IS_ENABLED(CONFIG_KVM_SMM))
+ return false;
/* SEV-ES guests do not support SMM, so report false */
if (kvm && sev_es_guest(kvm))
return false;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index b459ddf30abd..c2abe62d7cc0 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6841,6 +6841,8 @@ static bool vmx_has_emulated_msr(struct kvm *kvm, u32 index)
{
switch (index) {
case MSR_IA32_SMBASE:
+ if (!IS_ENABLED(CONFIG_KVM_SMM))
+ return false;
/*
* We cannot do SMM unless we can run the guest in big
* real mode.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ec5e9a837a12..3ec3d3632316 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3641,7 +3641,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
break;
}
case MSR_IA32_SMBASE:
- if (!msr_info->host_initiated)
+ if (!IS_ENABLED(CONFIG_KVM_SMM) || !msr_info->host_initiated)
return 1;
vcpu->arch.smbase = data;
break;
@@ -4057,7 +4057,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
msr_info->data = vcpu->arch.ia32_misc_enable_msr;
break;
case MSR_IA32_SMBASE:
- if (!msr_info->host_initiated)
+ if (!IS_ENABLED(CONFIG_KVM_SMM) || !msr_info->host_initiated)
return 1;
msr_info->data = vcpu->arch.smbase;
break;
@@ -4431,6 +4431,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r |= KVM_X86_DISABLE_EXITS_MWAIT;
break;
case KVM_CAP_X86_SMM:
+ if (!IS_ENABLED(CONFIG_KVM_SMM))
+ break;
+
/* SMBASE is usually relocated above 1M on modern chipsets,
* and SMM handlers might indeed rely on 4G segment limits,
* so do not report SMM to be available if real mode is
@@ -5181,6 +5184,7 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
vcpu->arch.apic->sipi_vector = events->sipi_vector;

if (events->flags & KVM_VCPUEVENT_VALID_SMM) {
+#ifdef CONFIG_KVM_SMM
if (!!(vcpu->arch.hflags & HF_SMM_MASK) != events->smi.smm) {
kvm_x86_ops.nested_ops->leave_nested(vcpu);
kvm_smm_changed(vcpu, events->smi.smm);
@@ -5195,6 +5199,12 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
vcpu->arch.hflags &= ~HF_SMM_INSIDE_NMI_MASK;
}

+#else
+ if (events->smi.smm || events->smi.pending ||
+ events->smi.smm_inside_nmi)
+ return -EINVAL;
+#endif
+
if (lapic_in_kernel(vcpu)) {
if (events->smi.latched_init)
set_bit(KVM_APIC_INIT, &vcpu->arch.apic->pending_events);
@@ -8120,6 +8130,14 @@ static unsigned emulator_get_hflags(struct x86_emulate_ctxt *ctxt)
return emul_to_vcpu(ctxt)->arch.hflags;
}

+#ifndef CONFIG_KVM_SMM
+static int emulator_leave_smm(struct x86_emulate_ctxt *ctxt)
+{
+ WARN_ON_ONCE(1);
+ return X86EMUL_UNHANDLEABLE;
+}
+#endif
+
static void emulator_triple_fault(struct x86_emulate_ctxt *ctxt)
{
kvm_make_request(KVM_REQ_TRIPLE_FAULT, emul_to_vcpu(ctxt));
diff --git a/tools/testing/selftests/kvm/x86_64/smm_test.c b/tools/testing/selftests/kvm/x86_64/smm_test.c
index 1f136a81858e..cb38a478e1f6 100644
--- a/tools/testing/selftests/kvm/x86_64/smm_test.c
+++ b/tools/testing/selftests/kvm/x86_64/smm_test.c
@@ -137,6 +137,8 @@ int main(int argc, char *argv[])
struct kvm_x86_state *state;
int stage, stage_reported;

+ TEST_REQUIRE(kvm_has_cap(KVM_CAP_X86_SMM));
+
/* Create VM */
vm = vm_create_with_one_vcpu(&vcpu, guest_code);

--
2.31.1