[PATCH] Add GDT, IDT and RFLAGS guest state validity checks

[Mohammed Gamal <m.gamal005@gmail.com>]

With emulate_invalid_guest_state=1 Windows XP exits with an invalid guest state
due to rflags not being in a VMX-compliant state. This patch fixes this issue,
although Windows XP doesn't boot yet with invalid state emulation on.

Also added GDT and IDT checks while we're at it.

Signed-off-by: Mohammed Gamal <m.gamal005@gmail.com>
---
 arch/x86/kvm/vmx.c |   57 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 56 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3fe0d42..eaec4a5 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2022,6 +2022,23 @@ static bool ldtr_valid(struct kvm_vcpu *vcpu)
 	return true;
 }
 
+static bool gdtr_idtr_valid(struct kvm_vcpu *vcpu)
+{
+	struct descriptor_table gdt;
+	struct descriptor_table idt;
+
+	vmx_get_gdt(vcpu, &gdt);
+	vmx_get_idt(vcpu, &idt);
+
+	if (gdt.limit & 0xffff0000)
+		return false;
+
+	if (idt.limit & 0xffff0000)
+		return false;
+
+	return true;
+}
+
 static bool cs_ss_rpl_check(struct kvm_vcpu *vcpu)
 {
 	struct kvm_segment cs, ss;
@@ -2033,6 +2050,41 @@ static bool cs_ss_rpl_check(struct kvm_vcpu *vcpu)
 		 (ss.selector & SELECTOR_RPL_MASK));
 }
 
+static bool rflags_valid(struct kvm_vcpu *vcpu)
+{
+	unsigned long rflags;
+	u32 entry_intr_info;
+
+	rflags = vmcs_readl(GUEST_RFLAGS);
+	entry_intr_info = vmcs_read32(VM_ENTRY_INTR_INFO_FIELD);
+#ifdef CONFIG_X86_64
+	if (rflags & 0xffffffffffc00000)
+		return false;
+	if (is_long_mode(vcpu))
+		if (rflags & X86_EFLAGS_VM)
+			return false;	
+#else
+	if (rflags & 0xffc00000)
+		return false;
+#endif
+	if (rflags & 0x8000)
+		return false;
+	if (rflags & 0x20)
+		return false;
+	if (rflags & 0x8)
+		return false;
+	if (!(rflags & 0x2))
+		return false;
+
+	if ((entry_intr_info & INTR_INFO_INTR_TYPE_MASK) == INTR_TYPE_EXT_INTR 
+		&& (entry_intr_info & INTR_INFO_VALID_MASK)) {
+		if (!(rflags & X86_EFLAGS_IF))
+			return false;
+	}
+
+	return true;
+}
+
 /*
  * Check if guest state is valid. Returns true if valid, false if
  * not.
@@ -2077,8 +2129,11 @@ static bool guest_state_valid(struct kvm_vcpu *vcpu)
 	}
 	/* TODO:
 	 * - Add checks on RIP
-	 * - Add checks on RFLAGS
 	 */
+	if (!rflags_valid(vcpu))
+		return false;
+	if (!gdtr_idtr_valid(vcpu))
+		return false;
 
 	return true;
 }
-- 
1.6.0.4