[PATCH 2/2] firmware: coreboot: Export active CBFS partition

patrick.rudolph
2019-10-08T11:54:21Z

From: Patrick Rudolph <patrick.rudolph@9elements.com>

Expose the name of the active CBFS partition under
/sys/firmware/cbfs_active_partition

In case of Google's VBOOT[1] that currently can be one of:
"FW_MAIN_A", "FW_MAIN_B" or "COREBOOT"

Will be used by fwupd[2] to determinde the active partition in the
VBOOT A/B partition update scheme.

[1]: https://doc.coreboot.org/security/vboot/index.html
[2]: https://fwupd.org/

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
---
drivers/firmware/google/Kconfig | 10 ++
drivers/firmware/google/Makefile | 1 +
drivers/firmware/google/bootmedia-coreboot.c | 115 +++++++++++++++++++
drivers/firmware/google/coreboot_table.h | 13 +++
4 files changed, 139 insertions(+)
create mode 100644 drivers/firmware/google/bootmedia-coreboot.c

diff --git a/drivers/firmware/google/Kconfig b/drivers/firmware/google/Kconfig
index 5fbbd7b8fef6..f58b723d77de 100644
--- a/drivers/firmware/google/Kconfig
+++ b/drivers/firmware/google/Kconfig
@@ -82,4 +82,14 @@ config GOOGLE_FMAP
the coreboot table. If found, this binary file is exported to userland
in the file /sys/firmware/fmap.

+config GOOGLE_BOOTMEDIA
+ tristate "Coreboot bootmedia params access"
+ depends on GOOGLE_COREBOOT_TABLE
+ depends on GOOGLE_FMAP
+ help
+ This option enables the kernel to search for a boot media params
+ table, providing the active CBFS partition. If found, the name of
+ the partition is exported to userland in the file
+ /sys/firmware/cbfs_active_partition.
+
endif # GOOGLE_FIRMWARE
diff --git a/drivers/firmware/google/Makefile b/drivers/firmware/google/Makefile
index 6d31fe167700..e47c59376566 100644
--- a/drivers/firmware/google/Makefile
+++ b/drivers/firmware/google/Makefile
@@ -7,6 +7,7 @@ obj-$(CONFIG_GOOGLE_MEMCONSOLE) += memconsole.o
obj-$(CONFIG_GOOGLE_MEMCONSOLE_COREBOOT) += memconsole-coreboot.o
obj-$(CONFIG_GOOGLE_MEMCONSOLE_X86_LEGACY) += memconsole-x86-legacy.o
obj-$(CONFIG_GOOGLE_FMAP) += fmap-coreboot.o
+obj-$(CONFIG_GOOGLE_BOOTMEDIA) += bootmedia-coreboot.o

vpd-sysfs-y := vpd.o vpd_decode.o
obj-$(CONFIG_GOOGLE_VPD) += vpd-sysfs.o
diff --git a/drivers/firmware/google/bootmedia-coreboot.c b/drivers/firmware/google/bootmedia-coreboot.c
new file mode 100644
index 000000000000..09c0caedaf05
--- /dev/null
+++ b/drivers/firmware/google/bootmedia-coreboot.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * bootmedia-coreboot.c
+ *
+ * Exports the active VBOOT partition name through boot media params.
+ *
+ * Copyright 2012-2013 David Herrmann <dh.herrmann@gmail.com>
+ * Copyright 2017 Google Inc.
+ * Copyright 2019 Patrick Rudolph <patrick.rudolph@9elements.com>
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+
+#include "coreboot_table.h"
+#include "fmap-coreboot.h"
+
+#define CB_TAG_BOOT_MEDIA_PARAMS 0x30
+
+/* The current CBFS partition */
+static char *name;
+
+static ssize_t cbfs_active_partition_read(struct file *filp,
+ struct kobject *kobp,
+ struct bin_attribute *bin_attr,
+ char *buf,
+ loff_t pos, size_t count)
+{
+ if (!name)
+ return -ENODEV;
+
+ return memory_read_from_buffer(buf, count, &pos, name, strlen(name));
+}
+
+static int bmp_probe(struct coreboot_device *dev)
+{
+ struct lb_boot_media_params *b = &dev->bmp;
+ const char *tmp;
+
+ /* Sanity checks on the data we got */
+ if ((b->cbfs_offset == ~0) ||
+ b->cbfs_size == 0 ||
+ ((b->cbfs_offset + b->cbfs_size) > b->boot_media_size)) {
+ pr_warn("coreboot: Boot media params contains invalid data\n");
+ return -ENODEV;
+ }
+
+ tmp = coreboot_fmap_region_to_name(b->cbfs_offset, b->cbfs_size);
+ if (!tmp) {
+ pr_warn("coreboot: Active CBFS region not found in FMAP\n");
+ return -ENODEV;
+ }
+
+ name = devm_kmalloc(&dev->dev, strlen(tmp) + 2, GFP_KERNEL);
+ if (!name) {
+ kfree(tmp);
+ return -ENODEV;
+ }
+ snprintf(name, strlen(tmp) + 2, "%s\n", tmp);
+
+ kfree(tmp);
+
+ return 0;
+}
+
+static int bmp_remove(struct coreboot_device *dev)
+{
+ struct platform_device *pdev = dev_get_drvdata(&dev->dev);
+
+ platform_device_unregister(pdev);
+
+ return 0;
+}
+
+static struct coreboot_driver bmp_driver = {
+ .probe = bmp_probe,
+ .remove = bmp_remove,
+ .drv = {
+ .name = "bootmediaparams",
+ },
+ .tag = CB_TAG_BOOT_MEDIA_PARAMS,
+};
+
+static struct bin_attribute cbfs_partition_bin_attr = {
+ .attr = {.name = "cbfs_active_partition", .mode = 0444},
+ .read = cbfs_active_partition_read,
+};
+
+static int __init coreboot_bmp_init(void)
+{
+ int err;
+
+ err = sysfs_create_bin_file(firmware_kobj, &cbfs_partition_bin_attr);
+ if (err)
+ return err;
+
+ return coreboot_driver_register(&bmp_driver);
+}
+
+static void coreboot_bmp_exit(void)
+{
+ coreboot_driver_unregister(&bmp_driver);
+ sysfs_remove_bin_file(firmware_kobj, &cbfs_partition_bin_attr);
+}
+
+module_init(coreboot_bmp_init);
+module_exit(coreboot_bmp_exit);
+
+MODULE_AUTHOR("9elements Agency GmbH");
+MODULE_LICENSE("GPL");
diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
index 7b7b4a6eedda..a03e039425b8 100644
--- a/drivers/firmware/google/coreboot_table.h
+++ b/drivers/firmware/google/coreboot_table.h
@@ -59,6 +59,18 @@ struct lb_framebuffer {
u8 reserved_mask_size;
};

+/* coreboot table with TAG 0x30 */
+struct lb_boot_media_params {
+ u32 tag;
+ u32 size;
+
+ /* offsets are relative to start of boot media */
+ u64 fmap_offset;
+ u64 cbfs_offset;
+ u64 cbfs_size;
+ u64 boot_media_size;
+};
+
/* A device, additionally with information from coreboot. */
struct coreboot_device {
struct device dev;
@@ -66,6 +78,7 @@ struct coreboot_device {
struct coreboot_table_entry entry;
struct lb_cbmem_ref cbmem_ref;
struct lb_framebuffer framebuffer;
+ struct lb_boot_media_params bmp;
};
};

--
2.21.0