dm: add support to directly boot to a mapped device

Add a "create" module parameter, which allows device-mapper targets to
be configured at boot time. This enables early use of DM targets in the
boot process (as the root device or otherwise) without the need of an
initramfs.

The syntax used in the boot param is based on the concise format from
the dmsetup tool to follow the rule of least surprise:

	dmsetup table --concise /dev/mapper/lroot

Which is:
	dm-mod.create=<name>,<uuid>,<minor>,<flags>,<table>[,<table>+][;<name>,<uuid>,<minor>,<flags>,<table>[,<table>+]+]

Where,
	<name>		::= The device name.
	<uuid>		::= xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx | ""
	<minor>		::= The device minor number | ""
	<flags>		::= "ro" | "rw"
	<table>		::= <start_sector> <num_sectors> <target_type> <target_args>
	<target_type>	::= "verity" | "linear" | ...

For example, the following could be added in the boot parameters:
dm-mod.create="lroot,,,rw, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" root=/dev/dm-0

Only the targets that were tested are allowed and the ones that don't
change any block device when the device is create as read-only. For
example, mirror and cache targets are not allowed. The rationale behind
this is that if the user makes a mistake, choosing the wrong device to
be the mirror or the cache can corrupt data.

The only targets initially allowed are:
* crypt
* delay
* linear
* snapshot-origin
* striped
* verity

Co-developed-by: Will Drewry <wad@chromium.org>
Co-developed-by: Kees Cook <keescook@chromium.org>
Co-developed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Helen Koike <helen.koike@collabora.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 103 insertions, 0 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index f666778ad237..c740153b4e52 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -2018,3 +2018,106 @@ out:
 
 	return r;
 }
+
+
+/**
+ * dm_early_create - create a mapped device in early boot.
+ *
+ * @dmi: Contains main information of the device mapping to be created.
+ * @spec_array: array of pointers to struct dm_target_spec. Describes the
+ * mapping table of the device.
+ * @target_params_array: array of strings with the parameters to a specific
+ * target.
+ *
+ * Instead of having the struct dm_target_spec and the parameters for every
+ * target embedded at the end of struct dm_ioctl (as performed in a normal
+ * ioctl), pass them as arguments, so the caller doesn't need to serialize them.
+ * The size of the spec_array and target_params_array is given by
+ * @dmi->target_count.
+ * This function is supposed to be called in early boot, so locking mechanisms
+ * to protect against concurrent loads are not required.
+ */
+int __init dm_early_create(struct dm_ioctl *dmi,
+			   struct dm_target_spec **spec_array,
+			   char **target_params_array)
+{
+	int r, m = DM_ANY_MINOR;
+	struct dm_table *t, *old_map;
+	struct mapped_device *md;
+	unsigned int i;
+
+	if (!dmi->target_count)
+		return -EINVAL;
+
+	r = check_name(dmi->name);
+	if (r)
+		return r;
+
+	if (dmi->flags & DM_PERSISTENT_DEV_FLAG)
+		m = MINOR(huge_decode_dev(dmi->dev));
+
+	/* alloc dm device */
+	r = dm_create(m, &md);
+	if (r)
+		return r;
+
+	/* hash insert */
+	r = dm_hash_insert(dmi->name, *dmi->uuid ? dmi->uuid : NULL, md);
+	if (r)
+		goto err_destroy_dm;
+
+	/* alloc table */
+	r = dm_table_create(&t, get_mode(dmi), dmi->target_count, md);
+	if (r)
+		goto err_destroy_dm;
+
+	/* add targets */
+	for (i = 0; i < dmi->target_count; i++) {
+		r = dm_table_add_target(t, spec_array[i]->target_type,
+					(sector_t) spec_array[i]->sector_start,
+					(sector_t) spec_array[i]->length,
+					target_params_array[i]);
+		if (r) {
+			DMWARN("error adding target to table");
+			goto err_destroy_table;
+		}
+	}
+
+	/* finish table */
+	r = dm_table_complete(t);
+	if (r)
+		goto err_destroy_table;
+
+	md->type = dm_table_get_type(t);
+	/* setup md->queue to reflect md's type (may block) */
+	r = dm_setup_md_queue(md, t);
+	if (r) {
+		DMWARN("unable to set up device queue for new table.");
+		goto err_destroy_table;
+	}
+
+	/* Set new map */
+	dm_suspend(md, 0);
+	old_map = dm_swap_table(md, t);
+	if (IS_ERR(old_map)) {
+		r = PTR_ERR(old_map);
+		goto err_destroy_table;
+	}
+	set_disk_ro(dm_disk(md), !!(dmi->flags & DM_READONLY_FLAG));
+
+	/* resume device */
+	r = dm_resume(md);
+	if (r)
+		goto err_destroy_table;
+
+	DMINFO("%s (%s) is ready", md->disk->disk_name, dmi->name);
+	dm_put(md);
+	return 0;
+
+err_destroy_table:
+	dm_table_destroy(t);
+err_destroy_dm:
+	dm_put(md);
+	dm_destroy(md);
+	return r;
+}