[PATCH v9] firmware: google: Implement cbmem in sysfs driver
From: Jack Rosenthal
Date: Mon Aug 15 2022 - 20:54:13 EST
The CBMEM area is a downward-growing memory region used by coreboot to
dynamically allocate tagged data structures ("CBMEM entries") that
remain resident during boot.
This implements a driver which exports access to the CBMEM entries
via sysfs under /sys/firmware/coreboot/cbmem/<id>.
This implementation is quite versatile. Examples of how it could be
used are given below:
* Tools like util/cbmem from the coreboot tree could use this driver
instead of finding CBMEM in /dev/mem directly. Alternatively,
firmware developers debugging an issue may find the sysfs interface
more ergonomic than the cbmem tool and choose to use it directly.
* The crossystem tool, which exposes verified boot variables, can use
this driver to read the vboot work buffer.
* Tools which read the BIOS SPI flash (e.g., flashrom) can find the
flash layout in CBMEM directly, which is significantly faster than
searching the flash directly.
Link: https://issuetracker.google.com/239604743
Cc: Stephen Boyd <swboyd@xxxxxxxxxxxx>
Cc: Tzung-Bi Shih <tzungbi@xxxxxxxxxx>
Reviewed-by: Guenter Roeck <groeck@xxxxxxxxxxxx>
Reviewed-by: Julius Werner <jwerner@xxxxxxxxxxxx>
Tested-by: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
Signed-off-by: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
---
v9:
* Removed unnecessary include linux/ctype.h.
* Made /sys/firmware/coreboot/cbmem/<id>/mem provide read-only access
only, and the permissions are now 0400.
* Added .owner = THIS_MODULE.
* Corrected coreboot_kobj -> cbmem_kobj.
* Updated Kconfig help message.
* Updated commit message to add much mode detail.
.../ABI/testing/sysfs-firmware-coreboot | 49 ++++
drivers/firmware/google/Kconfig | 8 +
drivers/firmware/google/Makefile | 3 +
drivers/firmware/google/cbmem.c | 215 ++++++++++++++++++
drivers/firmware/google/coreboot_table.c | 10 +
drivers/firmware/google/coreboot_table.h | 16 ++
6 files changed, 301 insertions(+)
create mode 100644 Documentation/ABI/testing/sysfs-firmware-coreboot
create mode 100644 drivers/firmware/google/cbmem.c
diff --git a/Documentation/ABI/testing/sysfs-firmware-coreboot b/Documentation/ABI/testing/sysfs-firmware-coreboot
new file mode 100644
index 000000000000..5432dea2408c
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-firmware-coreboot
@@ -0,0 +1,49 @@
+What: /sys/firmware/coreboot/
+Date: August 2022
+Contact: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
+Description:
+ Kernel objects associated with the Coreboot-based BIOS firmware.
+
+What: /sys/firmware/coreboot/cbmem/
+Date: August 2022
+Contact: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
+Description:
+ Coreboot provides a variety of information in CBMEM. This
+ directory contains each CBMEM entry, which can be found via
+ Coreboot tables.
+
+What: /sys/firmware/coreboot/cbmem/<id>/
+Date: August 2022
+Contact: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
+Description:
+ Each CBMEM entry is given a directory based on the id
+ corresponding to the entry. A list of ids known to coreboot can
+ be found in the coreboot source tree at
+ ``src/commonlib/bsd/include/commonlib/bsd/cbmem_id.h``.
+
+What: /sys/firmware/coreboot/cbmem/<id>/address
+Date: August 2022
+Contact: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
+Description:
+ The memory address that the CBMEM entry's data begins at.
+
+What: /sys/firmware/coreboot/cbmem/<id>/size
+Date: August 2022
+Contact: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
+Description:
+ The size of the data being stored.
+
+What: /sys/firmware/coreboot/cbmem/<id>/id
+Date: August 2022
+Contact: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
+Description:
+ The CBMEM id corresponding to the entry.
+
+What: /sys/firmware/coreboot/cbmem/<id>/mem
+Date: August 2022
+Contact: Jack Rosenthal <jrosenth@xxxxxxxxxxxx>
+Description:
+ A file exposing read-only access to the entry's data. Note
+ that this file does not support mmap(), and should be used for
+ basic data access only. Users requiring mmap() should read the
+ address and size files, and mmap() /dev/mem.
diff --git a/drivers/firmware/google/Kconfig b/drivers/firmware/google/Kconfig
index 983e07dc022e..b0f7a24fd90a 100644
--- a/drivers/firmware/google/Kconfig
+++ b/drivers/firmware/google/Kconfig
@@ -19,6 +19,14 @@ config GOOGLE_SMI
driver provides an interface for reading and writing NVRAM
variables.
+config GOOGLE_CBMEM
+ tristate "CBMEM entries in sysfs"
+ depends on GOOGLE_COREBOOT_TABLE
+ help
+ This option enables the kernel to search for Coreboot CBMEM
+ entries, and expose the memory for each entry in sysfs under
+ /sys/firmware/coreboot/cbmem.
+
config GOOGLE_COREBOOT_TABLE
tristate "Coreboot Table Access"
depends on HAS_IOMEM && (ACPI || OF)
diff --git a/drivers/firmware/google/Makefile b/drivers/firmware/google/Makefile
index d17caded5d88..8151e323cc43 100644
--- a/drivers/firmware/google/Makefile
+++ b/drivers/firmware/google/Makefile
@@ -7,5 +7,8 @@ obj-$(CONFIG_GOOGLE_MEMCONSOLE) += memconsole.o
obj-$(CONFIG_GOOGLE_MEMCONSOLE_COREBOOT) += memconsole-coreboot.o
obj-$(CONFIG_GOOGLE_MEMCONSOLE_X86_LEGACY) += memconsole-x86-legacy.o
+# Must come after coreboot_table.o, as this driver depends on that bus type.
+obj-$(CONFIG_GOOGLE_CBMEM) += cbmem.o
+
vpd-sysfs-y := vpd.o vpd_decode.o
obj-$(CONFIG_GOOGLE_VPD) += vpd-sysfs.o
diff --git a/drivers/firmware/google/cbmem.c b/drivers/firmware/google/cbmem.c
new file mode 100644
index 000000000000..cbfe8f388097
--- /dev/null
+++ b/drivers/firmware/google/cbmem.c
@@ -0,0 +1,215 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * cbmem.c
+ *
+ * Driver for exporting cbmem entries in sysfs.
+ *
+ * Copyright 2022 Google LLC
+ */
+
+#include <linux/device.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/kobject.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/sysfs.h>
+
+#include "coreboot_table.h"
+
+#define LB_TAG_CBMEM_ENTRY 0x31
+
+static struct kobject *cbmem_kobj;
+
+struct cbmem_entry;
+struct cbmem_entry_attr {
+ struct kobj_attribute kobj_attr;
+ struct cbmem_entry *entry;
+};
+
+struct cbmem_entry {
+ struct kobject *kobj;
+ struct coreboot_device *dev;
+ struct bin_attribute mem_file;
+ char *mem_file_buf;
+ struct cbmem_entry_attr address_file;
+ struct cbmem_entry_attr size_file;
+ struct cbmem_entry_attr id_file;
+};
+
+static struct cbmem_entry_attr *to_cbmem_entry_attr(struct kobj_attribute *a)
+{
+ return container_of(a, struct cbmem_entry_attr, kobj_attr);
+}
+
+static ssize_t cbmem_entry_mem_read(struct file *filp, struct kobject *kobp,
+ struct bin_attribute *bin_attr, char *buf,
+ loff_t pos, size_t count)
+{
+ struct cbmem_entry *entry = bin_attr->private;
+
+ return memory_read_from_buffer(buf, count, &pos, entry->mem_file_buf,
+ bin_attr->size);
+}
+
+static ssize_t cbmem_entry_address_show(struct kobject *kobj,
+ struct kobj_attribute *a, char *buf)
+{
+ struct cbmem_entry_attr *entry_attr = to_cbmem_entry_attr(a);
+
+ return sysfs_emit(buf, "0x%llx\n",
+ entry_attr->entry->dev->cbmem_entry.address);
+}
+
+static ssize_t cbmem_entry_size_show(struct kobject *kobj,
+ struct kobj_attribute *a, char *buf)
+{
+ struct cbmem_entry_attr *entry_attr = to_cbmem_entry_attr(a);
+
+ return sysfs_emit(buf, "0x%x\n",
+ entry_attr->entry->dev->cbmem_entry.entry_size);
+}
+
+static ssize_t cbmem_entry_id_show(struct kobject *kobj,
+ struct kobj_attribute *a, char *buf)
+{
+ struct cbmem_entry_attr *entry_attr = to_cbmem_entry_attr(a);
+
+ return sysfs_emit(buf, "0x%08x\n",
+ entry_attr->entry->dev->cbmem_entry.id);
+}
+
+static int cbmem_entry_setup(struct cbmem_entry *entry)
+{
+ int ret;
+ char *kobj_name;
+
+ entry->mem_file_buf =
+ devm_memremap(&entry->dev->dev, entry->dev->cbmem_entry.address,
+ entry->dev->cbmem_entry.entry_size, MEMREMAP_WB);
+ if (!entry->mem_file_buf)
+ return -ENOMEM;
+
+ kobj_name = devm_kasprintf(&entry->dev->dev, GFP_KERNEL, "%08x",
+ entry->dev->cbmem_entry.id);
+ if (!kobj_name)
+ return -ENOMEM;
+
+ entry->kobj = kobject_create_and_add(kobj_name, cbmem_kobj);
+ if (!entry->kobj)
+ return -ENOMEM;
+
+ sysfs_bin_attr_init(&entry->mem_file);
+ entry->mem_file.attr.name = "mem";
+ entry->mem_file.attr.mode = 0400;
+ entry->mem_file.size = entry->dev->cbmem_entry.entry_size;
+ entry->mem_file.read = cbmem_entry_mem_read;
+ entry->mem_file.private = entry;
+ ret = sysfs_create_bin_file(entry->kobj, &entry->mem_file);
+ if (ret)
+ goto free_kobj;
+
+ sysfs_attr_init(&entry->address_file.kobj_attr.attr);
+ entry->address_file.kobj_attr.attr.name = "address";
+ entry->address_file.kobj_attr.attr.mode = 0444;
+ entry->address_file.kobj_attr.show = cbmem_entry_address_show;
+ entry->address_file.entry = entry;
+ ret = sysfs_create_file(entry->kobj,
+ &entry->address_file.kobj_attr.attr);
+ if (ret)
+ goto free_mem_file;
+
+ sysfs_attr_init(&entry->size_file.kobj_attr.attr);
+ entry->size_file.kobj_attr.attr.name = "size";
+ entry->size_file.kobj_attr.attr.mode = 0444;
+ entry->size_file.kobj_attr.show = cbmem_entry_size_show;
+ entry->size_file.entry = entry;
+ ret = sysfs_create_file(entry->kobj, &entry->size_file.kobj_attr.attr);
+ if (ret)
+ goto free_address_file;
+
+ sysfs_attr_init(&entry->id_file.kobj_attr.attr);
+ entry->id_file.kobj_attr.attr.name = "id";
+ entry->id_file.kobj_attr.attr.mode = 0444;
+ entry->id_file.kobj_attr.show = cbmem_entry_id_show;
+ entry->id_file.entry = entry;
+ ret = sysfs_create_file(entry->kobj, &entry->id_file.kobj_attr.attr);
+ if (ret)
+ goto free_size_file;
+
+ return 0;
+
+free_size_file:
+ sysfs_remove_file(entry->kobj, &entry->size_file.kobj_attr.attr);
+free_address_file:
+ sysfs_remove_file(entry->kobj, &entry->address_file.kobj_attr.attr);
+free_mem_file:
+ sysfs_remove_bin_file(entry->kobj, &entry->mem_file);
+free_kobj:
+ kobject_put(entry->kobj);
+ return ret;
+}
+
+static int cbmem_entry_probe(struct coreboot_device *dev)
+{
+ struct cbmem_entry *entry;
+
+ entry = devm_kzalloc(&dev->dev, sizeof(*entry), GFP_KERNEL);
+ if (!entry)
+ return -ENOMEM;
+
+ dev_set_drvdata(&dev->dev, entry);
+ entry->dev = dev;
+ return cbmem_entry_setup(entry);
+}
+
+static void cbmem_entry_remove(struct coreboot_device *dev)
+{
+ struct cbmem_entry *entry = dev_get_drvdata(&dev->dev);
+
+ sysfs_remove_bin_file(entry->kobj, &entry->mem_file);
+ sysfs_remove_file(entry->kobj, &entry->address_file.kobj_attr.attr);
+ sysfs_remove_file(entry->kobj, &entry->size_file.kobj_attr.attr);
+ sysfs_remove_file(entry->kobj, &entry->id_file.kobj_attr.attr);
+ kobject_put(entry->kobj);
+}
+
+static struct coreboot_driver cbmem_entry_driver = {
+ .probe = cbmem_entry_probe,
+ .remove = cbmem_entry_remove,
+ .drv = {
+ .name = "cbmem",
+ .owner = THIS_MODULE,
+ },
+ .tag = LB_TAG_CBMEM_ENTRY,
+};
+
+static int __init cbmem_init(void)
+{
+ int ret;
+
+ cbmem_kobj = kobject_create_and_add("cbmem", coreboot_kobj);
+ if (!cbmem_kobj)
+ return -ENOMEM;
+
+ ret = coreboot_driver_register(&cbmem_entry_driver);
+ if (ret) {
+ kobject_put(cbmem_kobj);
+ return ret;
+ }
+
+ return 0;
+}
+module_init(cbmem_init);
+
+static void __exit cbmem_exit(void)
+{
+ kobject_put(cbmem_kobj);
+ coreboot_driver_unregister(&cbmem_entry_driver);
+}
+module_exit(cbmem_exit);
+
+MODULE_AUTHOR("Jack Rosenthal <jrosenth@xxxxxxxxxxxx>");
+MODULE_LICENSE("GPL");
diff --git a/drivers/firmware/google/coreboot_table.c b/drivers/firmware/google/coreboot_table.c
index c52bcaa9def6..a3e2720e4638 100644
--- a/drivers/firmware/google/coreboot_table.c
+++ b/drivers/firmware/google/coreboot_table.c
@@ -14,16 +14,21 @@
#include <linux/init.h>
#include <linux/io.h>
#include <linux/kernel.h>
+#include <linux/kobject.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
+#include <linux/sysfs.h>
#include "coreboot_table.h"
#define CB_DEV(d) container_of(d, struct coreboot_device, dev)
#define CB_DRV(d) container_of(d, struct coreboot_driver, drv)
+struct kobject *coreboot_kobj;
+EXPORT_SYMBOL(coreboot_kobj);
+
static int coreboot_bus_match(struct device *dev, struct device_driver *drv)
{
struct coreboot_device *device = CB_DEV(dev);
@@ -157,6 +162,10 @@ static int coreboot_table_probe(struct platform_device *pdev)
}
memunmap(ptr);
+ coreboot_kobj = kobject_create_and_add("coreboot", firmware_kobj);
+ if (!coreboot_kobj)
+ return -ENOMEM;
+
return ret;
}
@@ -170,6 +179,7 @@ static int coreboot_table_remove(struct platform_device *pdev)
{
bus_for_each_dev(&coreboot_bus_type, NULL, NULL, __cb_dev_unregister);
bus_unregister(&coreboot_bus_type);
+ kobject_put(coreboot_kobj);
return 0;
}
diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
index beb778674acd..76c31e6e5376 100644
--- a/drivers/firmware/google/coreboot_table.h
+++ b/drivers/firmware/google/coreboot_table.h
@@ -14,6 +14,11 @@
#include <linux/device.h>
+struct kobject;
+
+/* This is /sys/firmware/coreboot */
+extern struct kobject *coreboot_kobj;
+
/* Coreboot table header structure */
struct coreboot_table_header {
char signature[4];
@@ -39,6 +44,16 @@ struct lb_cbmem_ref {
u64 cbmem_addr;
};
+/* Corresponds to LB_TAG_CBMEM_ENTRY */
+struct lb_cbmem_entry {
+ u32 tag;
+ u32 size;
+
+ u64 address;
+ u32 entry_size;
+ u32 id;
+};
+
/* Describes framebuffer setup by coreboot */
struct lb_framebuffer {
u32 tag;
@@ -65,6 +80,7 @@ struct coreboot_device {
union {
struct coreboot_table_entry entry;
struct lb_cbmem_ref cbmem_ref;
+ struct lb_cbmem_entry cbmem_entry;
struct lb_framebuffer framebuffer;
};
};
--
2.37.1.595.g718a3a8f04-goog