diff --git a/block/sed-opal.c b/block/sed-opal.c
index f94f359..b02ef2f 100644
--- a/block/sed-opal.c
+++ b/block/sed-opal.c
@@ -26,6 +26,9 @@
 #define IO_BUFFER_LENGTH 2048
 #define MAX_TOKS 64
 
+/* Number of bytes needed by cmd_finalize. */
+#define CMD_FINALIZE_BYTES_NEEDED 7
+
 struct opal_step {
 	int (*fn)(struct opal_dev *dev, void *data);
 	void *data;
@@ -523,12 +526,17 @@ static int opal_discovery0_step(struct opal_dev *dev)
 	return execute_step(dev, &discovery0_step, 0);
 }
 
+static size_t remaining_size(struct opal_dev *cmd)
+{
+	return IO_BUFFER_LENGTH - cmd->pos;
+}
+
 static bool can_add(int *err, struct opal_dev *cmd, size_t len)
 {
 	if (*err)
 		return false;
 
-	if (len > IO_BUFFER_LENGTH || cmd->pos > IO_BUFFER_LENGTH - len) {
+	if (remaining_size(cmd) < len) {
 		pr_debug("Error adding %zu bytes: end of buffer.\n", len);
 		*err = -ERANGE;
 		return false;
@@ -674,7 +682,11 @@ static int cmd_finalize(struct opal_dev *cmd, u32 hsn, u32 tsn)
 	struct opal_header *hdr;
 	int err = 0;
 
-	/* close the parameter list opened from cmd_start */
+	/*
+	 * Close the parameter list opened from cmd_start.
+	 * The number of bytes added must be equal to
+	 * CMD_FINALIZE_BYTES_NEEDED.
+	 */
 	add_token_u8(&err, cmd, OPAL_ENDLIST);
 
 	add_token_u8(&err, cmd, OPAL_ENDOFDATA);
@@ -1536,6 +1548,58 @@ static int set_mbr_enable_disable(struct opal_dev *dev, void *data)
 	return finalize_and_send(dev, parse_and_check_status);
 }
 
+static int write_shadow_mbr(struct opal_dev *dev, void *data)
+{
+	struct opal_shadow_mbr *shadow = data;
+	const u8 __user *src;
+	u8 *dst;
+	size_t off = 0;
+	u64 len;
+	int err = 0;
+
+	/* do the actual transmission(s) */
+	src = (u8 __user *)(uintptr_t)shadow->data;
+	while (off < shadow->size) {
+		err = cmd_start(dev, opaluid[OPAL_MBR], opalmethod[OPAL_SET]);
+		add_token_u8(&err, dev, OPAL_STARTNAME);
+		add_token_u8(&err, dev, OPAL_WHERE);
+		add_token_u64(&err, dev, shadow->offset + off);
+		add_token_u8(&err, dev, OPAL_ENDNAME);
+
+		add_token_u8(&err, dev, OPAL_STARTNAME);
+		add_token_u8(&err, dev, OPAL_VALUES);
+
+		/*
+		 * The bytestring header is either 1 or 2 bytes, so assume 2.
+		 * There also needs to be enough space to accommodate the
+		 * trailing OPAL_ENDNAME (1 byte) and tokens added by
+		 * cmd_finalize.
+		 */
+		len = min(remaining_size(dev) - (2+1+CMD_FINALIZE_BYTES_NEEDED),
+			  (size_t)(shadow->size - off));
+		pr_debug("MBR: write bytes %zu+%llu/%llu\n",
+			 off, len, shadow->size);
+
+		dst = add_bytestring_header(&err, dev, len);
+		if (!dst)
+			break;
+		if (copy_from_user(dst, src + off, len))
+			err = -EFAULT;
+		dev->pos += len;
+
+		add_token_u8(&err, dev, OPAL_ENDNAME);
+		if (err)
+			break;
+
+		err = finalize_and_send(dev, parse_and_check_status);
+		if (err)
+			break;
+
+		off += len;
+	}
+	return err;
+}
+
 static int generic_pw_cmd(u8 *key, size_t key_len, u8 *cpin_uid,
 			  struct opal_dev *dev)
 {
@@ -2013,6 +2077,26 @@ static int opal_set_mbr_done(struct opal_dev *dev,
 	return ret;
 }
 
+static int opal_write_shadow_mbr(struct opal_dev *dev,
+				 struct opal_shadow_mbr *info)
+{
+	const struct opal_step mbr_steps[] = {
+		{ start_admin1LSP_opal_session, &info->key },
+		{ write_shadow_mbr, info },
+		{ end_opal_session, }
+	};
+	int ret;
+
+	if (info->size == 0)
+		return 0;
+
+	mutex_lock(&dev->dev_lock);
+	setup_opal_dev(dev);
+	ret = execute_steps(dev, mbr_steps, ARRAY_SIZE(mbr_steps));
+	mutex_unlock(&dev->dev_lock);
+	return ret;
+}
+
 static int opal_save(struct opal_dev *dev, struct opal_lock_unlock *lk_unlk)
 {
 	struct opal_suspend_data *suspend;
@@ -2337,6 +2421,9 @@ int sed_ioctl(struct opal_dev *dev, unsigned int cmd, void __user *arg)
 	case IOC_OPAL_MBR_DONE:
 		ret = opal_set_mbr_done(dev, p);
 		break;
+	case IOC_OPAL_WRITE_SHADOW_MBR:
+		ret = opal_write_shadow_mbr(dev, p);
+		break;
 	case IOC_OPAL_ERASE_LR:
 		ret = opal_erase_locking_range(dev, p);
 		break;