[SRU][Bionic][PATCH 4/6] KVM: X86: Allow userspace to define the microcode version

[Juerg Haefliger]

From: Wanpeng Li <wanpengli at tencent.com>

BugLink: https://bugs.launchpad.net/bugs/1822760

Linux (among the others) has checks to make sure that certain features
aren't enabled on a certain family/model/stepping if the microcode version
isn't greater than or equal to a known good version.

By exposing the real microcode version, we're preventing buggy guests that
don't check that they are running virtualized (i.e., they should trust the
hypervisor) from disabling features that are effectively not buggy.

Suggested-by: Filippo Sironi <sironi at amazon.de>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Cc: Radim Krčmář <rkrcmar at redhat.com>
Cc: Liran Alon <liran.alon at oracle.com>
Cc: Nadav Amit <nadav.amit at gmail.com>
Cc: Borislav Petkov <bp at alien8.de>
Cc: Tom Lendacky <thomas.lendacky at amd.com>
Signed-off-by: Wanpeng Li <wanpengli at tencent.com>
Reviewed-by: Paolo Bonzini <pbonzini at redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar at redhat.com>

(backported from commit 518e7b94817abed94becfe6a44f1ece0d4745afe)
[juergh:
 - Adjusted context.
 - rdmsrl -> rdmsrl_safe (to match final upstream).]
Signed-off-by: Juerg Haefliger <juergh at canonical.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/svm.c              |  4 +---
 arch/x86/kvm/vmx.c              |  1 +
 arch/x86/kvm/x86.c              | 11 +++++++++--
 4 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1a2309aeda6e..e76012ca0ddc 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -507,6 +507,7 @@ struct kvm_vcpu_arch {
 	u64 smbase;
 	bool tpr_access_reporting;
 	u64 ia32_xss;
+	u64 microcode_version;
 
 	/*
 	 * Paging state of the vcpu
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index ddca0a1175ab..4f9bd710bf5c 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1626,6 +1626,7 @@ static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	u32 dummy;
 	u32 eax = 1;
 
+	vcpu->arch.microcode_version = 0x01000065;
 	svm->spec_ctrl = 0;
 	svm->virt_spec_ctrl = 0;
 
@@ -3683,9 +3684,6 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 
 		msr_info->data = svm->spec_ctrl;
 		break;
-	case MSR_IA32_UCODE_REV:
-		msr_info->data = 0x01000065;
-		break;
 	case MSR_AMD64_VIRT_SPEC_CTRL:
 		if (!msr_info->host_initiated &&
 		    !guest_cpuid_has(vcpu, X86_FEATURE_VIRT_SSBD))
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1b135b6232cc..18c11b66acd5 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5937,6 +5937,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	vmx->rmode.vm86_active = 0;
 	vmx->spec_ctrl = 0;
 
+	vcpu->arch.microcode_version = 0x100000000ULL;
 	vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
 	kvm_set_cr8(vcpu, 0);
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a7e18f678bc5..058415af8de1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1054,6 +1054,7 @@ static unsigned num_emulated_msrs;
  */
 static u32 msr_based_features[] = {
 	MSR_F10H_DECFG,
+	MSR_IA32_UCODE_REV,
 	MSR_IA32_ARCH_CAPABILITIES,
 };
 
@@ -1087,6 +1088,9 @@ static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
 	case MSR_IA32_ARCH_CAPABILITIES:
 		msr->data = kvm_get_arch_capabilities();
 		break;
+	case MSR_IA32_UCODE_REV:
+		rdmsrl_safe(msr->index, &msr->data);
+		break;
 	default:
 		if (kvm_x86_ops->get_msr_feature(msr))
 			return 1;
@@ -2231,7 +2235,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 
 	switch (msr) {
 	case MSR_AMD64_NB_CFG:
-	case MSR_IA32_UCODE_REV:
 	case MSR_IA32_UCODE_WRITE:
 	case MSR_VM_HSAVE_PA:
 	case MSR_AMD64_PATCH_LOADER:
@@ -2239,6 +2242,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_AMD64_DC_CFG:
 		break;
 
+	case MSR_IA32_UCODE_REV:
+		if (msr_info->host_initiated)
+			vcpu->arch.microcode_version = data;
+		break;
 	case MSR_EFER:
 		return set_efer(vcpu, data);
 	case MSR_K7_HWCR:
@@ -2532,7 +2539,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = 0;
 		break;
 	case MSR_IA32_UCODE_REV:
-		msr_info->data = 0x100000000ULL;
+		msr_info->data = vcpu->arch.microcode_version;
 		break;
 	case MSR_IA32_TSC:
 		msr_info->data = kvm_scale_tsc(vcpu, rdtsc()) + vcpu->arch.tsc_offset;
-- 
2.19.1