[PATCH v3 21/25] KVM: TDX: Add tdx_get_cmd() helper to get and validate sub-ioctl command

[Sean Christopherson <seanjc@google.com>]

Add a helper to copy a kvm_tdx_cmd structure from userspace and verify
that must-be-zero fields are indeed zero.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/tdx.c | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 2e2dab89c98f..d5f810435f34 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -2761,20 +2761,25 @@ static int tdx_td_finalize(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
 	return 0;
 }
 
+static int tdx_get_cmd(void __user *argp, struct kvm_tdx_cmd *cmd)
+{
+	if (copy_from_user(cmd, argp, sizeof(*cmd)))
+		return -EFAULT;
+
+	if (cmd->hw_error)
+		return -EINVAL;
+
+	return 0;
+}
+
 int tdx_vm_ioctl(struct kvm *kvm, void __user *argp)
 {
 	struct kvm_tdx_cmd tdx_cmd;
 	int r;
 
-	if (copy_from_user(&tdx_cmd, argp, sizeof(struct kvm_tdx_cmd)))
-		return -EFAULT;
-
-	/*
-	 * Userspace should never set hw_error. It is used to fill
-	 * hardware-defined error by the kernel.
-	 */
-	if (tdx_cmd.hw_error)
-		return -EINVAL;
+	r = tdx_get_cmd(argp, &tdx_cmd);
+	if (r)
+		return r;
 
 	mutex_lock(&kvm->lock);
 
@@ -3152,11 +3157,9 @@ int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp)
 	if (!is_hkid_assigned(kvm_tdx) || kvm_tdx->state == TD_STATE_RUNNABLE)
 		return -EINVAL;
 
-	if (copy_from_user(&cmd, argp, sizeof(cmd)))
-		return -EFAULT;
-
-	if (cmd.hw_error)
-		return -EINVAL;
+	ret = tdx_get_cmd(argp, &cmd);
+	if (ret)
+		return ret;
 
 	switch (cmd.id) {
 	case KVM_TDX_INIT_VCPU:
-- 
2.51.0.858.gf9c4a03a3a-goog