x86/tdx: Add TDG.MR.KEY.GET ABI support

arch/x86/coco/tdx/tdx.c

@@ -178,6 +178,26 @@ int tdx_mcall_extend_rtmr(u8 index, u8 *data)
 }
 EXPORT_SYMBOL_GPL(tdx_mcall_extend_rtmr);
 
+/**
+ * tdx_mcall_key_get() - Wrapper to derive a persistent key for the TD,
+ *			 customized to the TD's measurements and policy
+ *			 using TDG.MR.KEY.GET TDCALL.
+ * @indata: Address of the input buffer with TDKEYREQUEST data.
+ * @outdata: Address of the output buffer with the requested key data.
+ *
+ * Return 0 on success or error code on other TDCALL failures.
+ */
+u64 tdx_mcall_key_get(u8 *indata, u8 *outdata)
+{
+	struct tdx_module_args args = {
+		.rcx = virt_to_phys(indata),
+		.rdx = virt_to_phys(outdata),
+	};
+
+	return __tdcall(TDG_MR_KEY_GET, &args);
+}
+EXPORT_SYMBOL_GPL(tdx_mcall_key_get);
+
 /**
  * tdx_hcall_get_quote() - Wrapper to request TD Quote using GetQuote
  *                         hypercall.

arch/x86/include/asm/shared/tdx.h

@@ -19,6 +19,7 @@
 #define TDG_MEM_PAGE_ACCEPT		6
 #define TDG_VM_RD			7
 #define TDG_VM_WR			8
+#define TDG_MR_KEY_GET			29
 
 /* TDX attributes */
 #define TDX_ATTR_DEBUG_BIT		0

arch/x86/include/asm/tdx.h

@@ -72,6 +72,8 @@ int tdx_mcall_get_report0(u8 *reportdata, u8 *tdreport);
 
 int tdx_mcall_extend_rtmr(u8 index, u8 *data);
 
+u64 tdx_mcall_key_get(u8 *indata, u8 *outdata);
+
 u64 tdx_hcall_get_quote(u8 *buf, size_t size);
 
 void __init tdx_dump_attributes(u64 td_attr);

drivers/virt/coco/tdx-guest/tdx-guest.c

@@ -206,6 +206,54 @@ static long tdx_get_report0(struct tdx_report_req __user *req)
 			     USER_SOCKPTR(req->tdreport));
 }
 
+static long tdx_key_get(struct tdx_key_get_req __user *req)
+{
+	u8 *indata = NULL, *outdata = NULL;
+	long ret = 0;
+	u64 err;
+
+	/*
+	 * TDG.MR.KEY.GET expects the TDKEYREQUEST input buffer to be 128B
+	 * aligned and the key output buffer to be 32B aligned. kmalloc()
+	 * guarantees alignment to the allocation size for power-of-two sizes,
+	 * and TDX_TDKEYREQ_LEN (128) and TDX_KEY_LEN (32) are both powers of
+	 * two, so the returned buffers meet the required alignment.
+	 */
+	indata = kmalloc(sizeof(req->tdkeyreq), GFP_KERNEL);
+	if (!indata)
+		return -ENOMEM;
+
+	outdata = kzalloc(sizeof(req->outkey), GFP_KERNEL);
+	if (!outdata) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	if (copy_from_user(indata, req->tdkeyreq, sizeof(req->tdkeyreq))) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	/* Get derived key using "TDG.MR.KEY.GET" TDCALL */
+	err = tdx_mcall_key_get(indata, outdata);
+	if (err) {
+		ret = -EIO;
+		if (copy_to_user(&req->err_code, &err, sizeof(u64)))
+			ret = -EFAULT;
+		goto out;
+	}
+
+	/* On success, write back the derived key and clear err_code (0) */
+	if (copy_to_user(&req->err_code, &err, sizeof(u64)) ||
+	    copy_to_user(&req->outkey, outdata, sizeof(req->outkey)))
+		ret = -EFAULT;
+
+out:
+	kfree_sensitive(indata);
+	kfree_sensitive(outdata);
+	return ret;
+}
+
 static void free_quote_buf(void *buf)
 {
 	size_t len = PAGE_ALIGN(GET_QUOTE_BUF_SIZE);
@@ -353,6 +401,8 @@ static long tdx_guest_ioctl(struct file *file, unsigned int cmd,
 	switch (cmd) {
 	case TDX_CMD_GET_REPORT0:
 		return tdx_get_report0((struct tdx_report_req __user *)arg);
+	case TDX_CMD_KEY_GET:
+		return tdx_key_get((struct tdx_key_get_req __user *)arg);
 	default:
 		return -ENOTTY;
 	}

include/uapi/linux/tdx-guest.h

@@ -17,6 +17,12 @@
 /* Length of TDREPORT used in TDG.MR.REPORT TDCALL */
 #define TDX_REPORT_LEN                  1024
 
+/* TDKEYREQ struct length */
+#define TDX_TDKEYREQ_LEN                128
+
+/* Length of the derived key */
+#define TDX_KEY_LEN                     32
+
 /**
  * struct tdx_report_req - Request struct for TDX_CMD_GET_REPORT0 IOCTL.
  *
@@ -30,6 +36,19 @@ struct tdx_report_req {
 	__u8 tdreport[TDX_REPORT_LEN];
 };
 
+/**
+ * struct tdx_key_get_req - Request struct for TDX_CMD_KEY_GET IOCTL.
+ *
+ * @tdkeyreq: TDKEYREQ struct.
+ * @outkey: Derived key output
+ * @err_code: TDG.MR.KEY.GET TDCALL return error code.
+ */
+struct tdx_key_get_req {
+	__u8 tdkeyreq[TDX_TDKEYREQ_LEN];
+	__u8 outkey[TDX_KEY_LEN];
+	__u64 err_code;
+};
+
 /*
  * TDX_CMD_GET_REPORT0 - Get TDREPORT0 (a.k.a. TDREPORT subtype 0) using
  *                       TDCALL[TDG.MR.REPORT]
@@ -39,4 +58,12 @@ struct tdx_report_req {
  */
 #define TDX_CMD_GET_REPORT0              _IOWR('T', 1, struct tdx_report_req)
 
+/*
+ * TDX_CMD_KEY_GET - Request to derive a persistent key for the TD,
+ *                   customized to the TD's measurements and policy.
+ *
+ * Returns 0 on success, and standard errno on other failures.
+ */
+#define TDX_CMD_KEY_GET                  _IOWR('T', 5, struct tdx_key_get_req)
+
 #endif /* _UAPI_LINUX_TDX_GUEST_H_ */