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Subject[PATCH v8 1/2] init: add support to directly boot to a mapped device
Date
From: Will Drewry <wad@chromium.org>

Add a dm= kernel parameter modeled after the md= parameter from
do_mounts_md. It allows for device-mapper targets to be configured at
boot time for use early in the boot process (as the root device or
otherwise).

Signed-off-by: Will Drewry <wad@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
[rework to use dm_ioctl calls]
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
---
Documentation/admin-guide/kernel-parameters.rst | 1 +
Documentation/admin-guide/kernel-parameters.txt | 3 +
Documentation/device-mapper/dm-boot.txt | 65 ++++
init/Makefile | 1 +
init/do_mounts.c | 1 +
init/do_mounts.h | 10 +
init/do_mounts_dm.c | 459 ++++++++++++++++++++++++
7 files changed, 540 insertions(+)
create mode 100644 Documentation/device-mapper/dm-boot.txt
create mode 100644 init/do_mounts_dm.c

diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst
index d76ab39..5301f45 100644
--- a/Documentation/admin-guide/kernel-parameters.rst
+++ b/Documentation/admin-guide/kernel-parameters.rst
@@ -92,6 +92,7 @@ parameter is applicable::
BLACKFIN Blackfin architecture is enabled.
CLK Common clock infrastructure is enabled.
CMA Contiguous Memory Area support is enabled.
+ DM Device mapper support is enabled.
DRM Direct Rendering Management support is enabled.
DYNAMIC_DEBUG Build in debug messages and enable them at runtime
EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f85bfe0..0ea65c2 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -829,6 +829,9 @@

dis_ucode_ldr [X86] Disable the microcode loader.

+ dm= [DM] Allows early creation of a device-mapper device.
+ See Documentation/device-mapper/boot.txt.
+
dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
this option disables the debugging code at boot.

diff --git a/Documentation/device-mapper/dm-boot.txt b/Documentation/device-mapper/dm-boot.txt
new file mode 100644
index 0000000..50f08ec
--- /dev/null
+++ b/Documentation/device-mapper/dm-boot.txt
@@ -0,0 +1,65 @@
+Boot time creation of mapped devices
+====================================
+
+It is possible to configure a device mapper device to act as the root
+device for your system in two ways.
+
+The first is to build an initial ramdisk which boots to a minimal
+userspace which configures the device, then pivot_root(8) in to it.
+
+The second is to possible when the device-mapper and any targets are
+compiled into the kernel (not a module), one or more device-mappers may
+be created and used as the root device at boot time with the parameters
+given with the boot line dm=...
+
+The format is specified as a simple string of data separated by commas and
+optionally semi-colons, where:
+ - a comma is used to separate fields like name, uuid, flags and table (specifies
+ one device)
+ - a semi-colon is used to separate devices.
+
+So the format will look like this:
+
+ dm=<dev_name>,<uuid>,<flags>,<table>[,<table>+][;<dev_name>,<uuid>,<flags>,<table>[,<table>+]]+
+
+Where,
+ <dev_name> ::= The device name.
+ <uuid> ::= xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx | ""
+ <flags> ::= "ro" | "rw"
+ <table> ::= <start> <length> <type> <options>
+ <type> ::= "verity" | "bootcache" | ...
+
+The dm line may be as normal when using the dmsetup tool when using the
+--bootformat argument.
+
+Unless renamed by udev, the device node created will be dm-0 as the
+first minor number for the device-mapper is used during early creation.
+
+Examples
+========
+An example of booting to a linear array made up of user-mode linux block
+devices:
+
+ dm="lroot,,rw, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" \
+ root=/dev/dm-0
+
+This will boot to a rw dm-linear target of 8192 sectors split across two
+block devices identified by their major:minor numbers. After boot, udev
+will rename this target to /dev/mapper/lroot (depending on the rules).
+No uuid was assigned.
+
+An example of multiple device-mappers, with the dm="..." contents shown
+here split on multiple lines for readability:
+
+ vboot,,ro,
+ 0 1768000 bootcache
+ aa55b119-2a47-8c45-946a-5ac57765011f+1
+ 76e9be054b15884a9fa85973e9cb274c93afadb6
+ 1768000 100000 23 20000;
+ vroot,,ro,
+ 0 1740800 verity 254:0 254:0 1740800 sha1
+ 76e9be054b15884a9fa85973e9cb274c93afadb6
+ 5b3549d54d6c7a3837b9b81ed72e49463a64c03680c47835bef94d768e5646fe;
+ vram,,rw,
+ 0 32768 linear 1:0 0,
+ 32768 32768 linear 1:1 0
diff --git a/init/Makefile b/init/Makefile
index c4fb455..30424d7 100644
--- a/init/Makefile
+++ b/init/Makefile
@@ -20,6 +20,7 @@ mounts-y := do_mounts.o
mounts-$(CONFIG_BLK_DEV_RAM) += do_mounts_rd.o
mounts-$(CONFIG_BLK_DEV_INITRD) += do_mounts_initrd.o
mounts-$(CONFIG_BLK_DEV_MD) += do_mounts_md.o
+mounts-$(CONFIG_BLK_DEV_DM) += do_mounts_dm.o

# dependencies on generated files need to be listed explicitly
$(obj)/version.o: include/generated/compile.h
diff --git a/init/do_mounts.c b/init/do_mounts.c
index c2de510..8b9182b 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -566,6 +566,7 @@ void __init prepare_namespace(void)
wait_for_device_probe();

md_run_setup();
+ dm_run_setup();

if (saved_root_name[0]) {
root_device_name = saved_root_name;
diff --git a/init/do_mounts.h b/init/do_mounts.h
index 282d65b..4e71c29 100644
--- a/init/do_mounts.h
+++ b/init/do_mounts.h
@@ -60,3 +60,13 @@ void md_run_setup(void);
static inline void md_run_setup(void) {}

#endif
+
+#ifdef CONFIG_BLK_DEV_DM
+
+void dm_run_setup(void);
+
+#else
+
+static inline void dm_run_setup(void) {}
+
+#endif
diff --git a/init/do_mounts_dm.c b/init/do_mounts_dm.c
new file mode 100644
index 0000000..87c4300
--- /dev/null
+++ b/init/do_mounts_dm.c
@@ -0,0 +1,459 @@
+/*
+ * do_mounts_dm.c
+ * Copyright (C) 2017 The Chromium OS Authors <chromium-os-dev@chromium.org>
+ * Based on do_mounts_md.c
+ *
+ * This file is released under the GPLv2.
+ */
+#include <linux/async.h>
+#include <linux/ctype.h>
+#include <linux/device-mapper.h>
+#include <linux/fs.h>
+#include <linux/string.h>
+#include <linux/delay.h>
+
+#include "do_mounts.h"
+
+#define DM_MAX_DEVICES 256
+#define DM_MAX_NAME 32
+#define DM_MAX_UUID 129
+
+#define DM_MSG_PREFIX "init"
+
+#define is_even(a) (((a) & 1) == 0)
+
+/* See Documentation/device-mapper/dm-boot.txt for dm="..." format details. */
+
+struct target {
+ sector_t start;
+ sector_t length;
+ char *type;
+ char *params;
+ /* simple singly linked list */
+ struct target *next;
+};
+
+struct dm_device {
+ int minor;
+ int ro;
+ char name[DM_MAX_NAME];
+ char uuid[DM_MAX_UUID];
+ struct target *table;
+ int table_count;
+ /* simple singly linked list */
+ struct dm_device *next;
+};
+
+static struct {
+ unsigned long num_devices;
+ char *str;
+} dm_setup_args __initdata;
+
+static int dm_early_setup __initdata;
+
+static void __init *_align(void *ptr, unsigned int a)
+{
+ register unsigned long agn = --a;
+
+ return (void *) (((unsigned long) ptr + agn) & ~agn);
+}
+
+/*
+ * Unescape characters in situ, it replaces all occurrences of "\c"
+ * with 'c'. This is normally used to unescape colons and semi-colons used
+ * in boot format.
+ */
+static char __init *_unescape_char(char *str, const char c)
+{
+ int i = 0, j = 0;
+ int len = strlen(str);
+
+ if (len < 2)
+ return str;
+
+ while (j < len - 1) {
+ if (str[j] == '\\' && str[j + 1] == c) {
+ j = j + 2;
+ str[i++] = c;
+ continue;
+ }
+ str[i++] = str[j++];
+ }
+
+ if (j == len - 1)
+ str[i++] = str[j];
+
+ str[i] = '\0';
+
+ return str;
+}
+
+static void __init dm_setup_cleanup(struct dm_device *devices)
+{
+ struct dm_device *dev = devices;
+
+ while (dev) {
+ struct dm_device *old_dev = dev;
+ struct target *table = dev->table;
+
+ while (table) {
+ struct target *old_table = table;
+
+ kfree(table->type);
+ kfree(table->params);
+ table = table->next;
+ kfree(old_table);
+ dev->table_count--;
+ }
+ WARN_ON(dev->table_count);
+ dev = dev->next;
+ kfree(old_dev);
+ }
+}
+
+/*
+ * Splits a string into tokens ignoring escaped chars
+ *
+ * Updates @s to point after the token, ready for the next call.
+ *
+ * @str: The string to be searched
+ * @c: The character to search for
+ *
+ * Returns:
+ * The string found or NULL.
+ */
+static char __init *dm_find_unescaped_char(char **str, const char c)
+{
+ char *s = *str;
+ char *p = strchr(*str, c);
+
+ /* loop through all the characters */
+ while (p != NULL) {
+ /* scan backwards through preceding escapes */
+ char *q = p;
+
+ while (q > s && *(q - 1) == '\\')
+ --q;
+ /* even number of escapes so c is a token */
+ if (is_even(p - q)) {
+ *p = '\0';
+ *str = p + 1;
+ return s;
+ }
+ /* else odd escapes so c is escaped, keep going */
+ p = strchr(p + 1, c);
+ }
+
+ if (strlen(*str)) {
+ *str += strlen(*str);
+ return s;
+ }
+
+ return NULL;
+}
+
+static struct target __init *dm_parse_table(struct dm_device *dev, char *str)
+{
+ char type[DM_MAX_TYPE_NAME], *ptr;
+ struct target *table;
+ int n;
+
+ /* trim trailing space */
+ for (ptr = str + strlen(str) - 1; ptr >= str; ptr--)
+ if (!isspace((int) *ptr))
+ break;
+ ptr++;
+ *ptr = '\0';
+
+ /* trim leading space */
+ for (ptr = str; *ptr && isspace((int) *ptr); ptr++)
+ ;
+
+ if (!*ptr)
+ return NULL;
+
+ table = kzalloc(sizeof(struct target), GFP_KERNEL);
+ if (!table)
+ return NULL;
+
+ if (sscanf(ptr, "%llu %llu %s %n", &table->start, &table->length,
+ type, &n) < 3) {
+ DMERR("invalid format of table \"%s\"", str);
+ goto parse_fail;
+ }
+
+ table->type = kstrndup(type, strlen(type), GFP_KERNEL);
+ if (!table->type) {
+ DMERR("invalid type of table");
+ goto parse_fail;
+ }
+
+ ptr += n;
+ table->params = kstrndup(ptr, strlen(ptr), GFP_KERNEL);
+ if (!table->params) {
+ DMERR("invalid params for table");
+ goto parse_fail;
+ }
+
+ dev->table_count++;
+
+ return table;
+
+parse_fail:
+ kfree(table);
+ return NULL;
+}
+
+static int __init dm_parse_device(struct dm_device *dev, char *dev_info)
+{
+ int field = 0;
+ char *str = dev_info, *ptr = dev_info;
+ struct target *table;
+ struct target **tail = &dev->table;
+
+ while ((str = dm_find_unescaped_char(&ptr, ',')) != NULL) {
+ str = _unescape_char(str, ',');
+ switch (field) {
+ case 0: /* set device name */
+ strncpy(dev->name, str, strlen(str));
+ break;
+ case 1: /* set uuid if any */
+ strncpy(dev->uuid, str, strlen(str));
+ break;
+ case 2:
+ /* set as read-only if flags = "ro" | "" */
+ if (!strncmp(str, "ro", strlen(str)) || !strlen(str))
+ dev->ro = 1;
+ else if (!strncmp(str, "rw", strlen(str)))
+ dev->ro = 0;
+ else
+ return -EINVAL;
+ break;
+ default:
+ table = dm_parse_table(dev, str);
+ if (!table)
+ goto parse_fail;
+
+ *tail = table;
+ tail = &table->next;
+
+ break;
+ }
+ field++;
+ }
+
+ if (field < 4)
+ goto parse_fail;
+
+ return 0;
+
+parse_fail:
+ return -EINVAL;
+}
+
+static struct dm_device __init *dm_parse_args(void)
+{
+ struct dm_device *devices = NULL;
+ struct dm_device **tail = &devices;
+ struct dm_device *dev;
+ char *dev_info, *str = dm_setup_args.str;
+
+ while ((dev_info = dm_find_unescaped_char(&str, ';')) != NULL) {
+ dev_info = _unescape_char(dev_info, ';');
+ dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+ if (!dev)
+ goto error;
+
+ if (dm_parse_device(dev, dev_info))
+ goto error;
+
+ *tail = dev;
+ tail = &dev->next;
+ /*
+ * devices are given minor numbers 0 - n-1 in the order they are
+ * found in the arg string.
+ */
+ dev->minor = dm_setup_args.num_devices++;
+
+ if (dm_setup_args.num_devices > DM_MAX_DEVICES) {
+ DMERR("too many devices %lu > %d",
+ dm_setup_args.num_devices, DM_MAX_DEVICES);
+ goto error;
+ }
+ }
+ return devices;
+error:
+ dm_setup_cleanup(devices);
+ return NULL;
+}
+
+/*
+ * Parse the command-line parameters given our kernel, but do not
+ * actually try to invoke the DM device now; that is handled by
+ * dm_setup_drives after the low-level disk drivers have initialised.
+ * dm format is described at the top of the file.
+ *
+ * Because dm minor numbers are assigned in ascending order starting with 0,
+ * You can assume the first device is /dev/dm-0, the next device is /dev/dm-1,
+ * and so forth.
+ */
+static int __init dm_setup(char *str)
+{
+ if (!str) {
+ DMERR("Invalid arguments supplied to dm=.");
+ return 0;
+ }
+
+ DMDEBUG("Want to parse \"%s\"", str);
+
+ dm_setup_args.num_devices = 0;
+ dm_setup_args.str = str;
+
+ dm_early_setup = 1;
+
+ return 1;
+}
+
+static char __init *dm_add_target(struct target *table, char *out, char *end)
+{
+ char *out_sp = out;
+ struct dm_target_spec sp;
+ size_t sp_size = sizeof(struct dm_target_spec);
+ int len;
+ char *pt;
+
+ if (strlen(table->type) >= sizeof(sp.target_type)) {
+ DMERR("target type name %s is too long.", table->type);
+ return NULL;
+ }
+
+ sp.status = 0;
+ sp.sector_start = table->start;
+ sp.length = table->length;
+ strncpy(sp.target_type, table->type, sizeof(sp.target_type) - 1);
+ sp.target_type[sizeof(sp.target_type) - 1] = '\0';
+
+ out += sp_size;
+ pt = table->params;
+ len = strlen(table->params);
+
+ if ((out >= end) || (out + len + 1) >= end) {
+ DMERR("ran out of memory building ioctl parameter");
+ return NULL;
+ }
+
+ strcpy(out, table->params);
+ out += len + 1;
+ /* align next block */
+ out = _align(out, 8);
+
+ sp.next = out - out_sp;
+ memcpy(out_sp, &sp, sp_size);
+
+ return out;
+}
+
+static struct dm_ioctl __init *dm_setup_ioctl(struct dm_device *dev, int flags)
+{
+ const size_t min_size = 16 * 1024;
+ size_t len = sizeof(struct dm_ioctl);
+ struct dm_ioctl *dmi;
+ struct target *table = dev->table;
+ char *b, *e;
+
+ if (len < min_size)
+ len = min_size;
+
+ dmi = kzalloc(len, GFP_KERNEL);
+ if (!dmi)
+ return NULL;
+
+ dmi->version[0] = 4;
+ dmi->version[1] = 0;
+ dmi->version[2] = 0;
+ dmi->data_size = len;
+ dmi->data_start = sizeof(struct dm_ioctl);
+ dmi->flags = flags;
+ dmi->dev = dev->minor;
+ dmi->target_count = dev->table_count;
+ dmi->event_nr = 1;
+
+ strncpy(dmi->name, dev->name, sizeof(dmi->name));
+
+ b = (char *) (dmi + 1);
+ e = (char *) dmi + len;
+
+ while (table != NULL) {
+ DMDEBUG("device %s adding table '%llu %llu %s %s'",
+ dev->name,
+ (unsigned long long) table->start,
+ (unsigned long long) table->length,
+ table->type, table->params);
+ b = dm_add_target(table, b, e);
+ if (!b)
+ return NULL;
+ table = table->next;
+ }
+
+ return dmi;
+}
+
+static void __init dm_setup_drives(void)
+{
+ struct dm_device *dev;
+ int flags;
+ struct dm_device *devices;
+ struct dm_ioctl *io = NULL;
+
+ devices = dm_parse_args();
+
+ for (dev = devices; dev; dev = dev->next) {
+ io = dm_setup_ioctl(dev, 0);
+ if (!io)
+ return;
+ /* create a new device */
+ if (dm_ioctl_cmd(DM_DEV_CREATE, io)) {
+ DMERR("failed to create device %s", dev->name);
+ goto out_free;
+ }
+ kfree(io);
+
+ flags = DM_STATUS_TABLE_FLAG;
+ if (dev->ro)
+ flags |= DM_READONLY_FLAG;
+
+ io = dm_setup_ioctl(dev, flags);
+ if (!io)
+ return;
+ /* load a table into the 'inactive' slot for the device. */
+ if (dm_ioctl_cmd(DM_TABLE_LOAD, io)) {
+ DMERR("failed to load device %s tables", dev->name);
+ goto out_free;
+ }
+ kfree(io);
+
+ io = dm_setup_ioctl(dev, 0);
+ if (!io)
+ return;
+ /* resume and the device should be ready. */
+ if (dm_ioctl_cmd(DM_DEV_SUSPEND, io)) {
+ DMERR("failed to resume device %s", dev->name);
+ goto out_free;
+ }
+
+ DMINFO("dm-%d (%s) is ready", dev->minor, dev->name);
+ }
+
+out_free:
+ kfree(io);
+}
+
+__setup("dm=", dm_setup);
+
+void __init dm_run_setup(void)
+{
+ if (!dm_early_setup)
+ return;
+ DMINFO("attempting early device configuration.");
+ dm_setup_drives();
+}
--
2.9.3
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