[PATCH 1/2 v3] KVM: nVMX: Check GUEST_DR7 on vmentry of nested guests

[Krish Sadhukhan <krish.sadhukhan@oracle.com>]

According to section "Checks on Guest Control Registers, Debug Registers, and
and MSRs" in Intel SDM vol 3C, the following checks are performed on vmentry
of nested guests:

    If the "load debug controls" VM-entry control is 1, bits 63:32 in the DR7
    field must be 0.

In KVM, GUEST_DR7 is set prior to the vmcs02 VM-entry by kvm_set_dr() and the
latter synthesizes a #GP if any bit in the high dword in the former is set.
Hence this field needs to be checked in software.

Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
---
 arch/x86/kvm/vmx/nested.c | 4 ++++
 arch/x86/kvm/x86.c        | 2 +-
 arch/x86/kvm/x86.h        | 6 ++++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 4aea7d304beb..a5ee49ab75d5 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2899,6 +2899,10 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
 	    CC(!nested_guest_cr4_valid(vcpu, vmcs12->guest_cr4)))
 		return -EINVAL;
 
+	if ((vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS) &&
+	    CC(!kvm_dr7_valid(vmcs12->guest_dr7)))
+		return -EINVAL;
+
 	if ((vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_PAT) &&
 	    CC(!kvm_pat_valid(vmcs12->guest_ia32_pat)))
 		return -EINVAL;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cf917139de6b..220f20a2f9c3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1064,7 +1064,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 	case 5:
 		/* fall through */
 	default: /* 7 */
-		if (val & 0xffffffff00000000ULL)
+		if (!kvm_dr7_valid(val))
 			return -1; /* #GP */
 		vcpu->arch.dr7 = (val & DR7_VOLATILE) | DR7_FIXED_1;
 		kvm_update_dr7(vcpu);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 29391af8871d..db42692bb209 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -369,6 +369,12 @@ static inline bool kvm_pat_valid(u64 data)
 	return (data | ((data & 0x0202020202020202ull) << 1)) == data;
 }
 
+static inline bool kvm_dr7_valid(unsigned long data)
+{
+	/* Bits [63:32] are reserved */
+	return !(data >> 32);
+}
+
 void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
 void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
 
-- 
2.20.1