KVM: nVMX: Fix consistency check on injected exception error code

[ Upstream commit 567926cca99ba1750be8aae9c4178796bf9bb90b ]

Current versions of Intel's SDM incorrectly state that "bits 31:15 of
the VM-Entry exception error-code field" must be zero.  In reality, bits
31:16 must be zero, i.e. error codes are 16-bit values.

The bogus error code check manifests as an unexpected VM-Entry failure
due to an invalid code field (error number 7) in L1, e.g. when injecting
a #GP with error_code=0x9f00.

Nadav previously reported the bug[*], both to KVM and Intel, and fixed
the associated kvm-unit-test.

[*] https://patchwork.kernel.org/patch/11124749/

Reported-by: Nadav Amit <namit@vmware.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/x86/kvm/vmx.c

@@ -12574,7 +12574,7 @@ static int check_vmentry_prereqs(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 
 		/* VM-entry exception error code */
 		if (has_error_code &&
-		    vmcs12->vm_entry_exception_error_code & GENMASK(31, 15))
+		    vmcs12->vm_entry_exception_error_code & GENMASK(31, 16))
 			return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
 
 		/* VM-entry interruption-info field: reserved bits */