[PATCH v10] firmware: google: Implement cbmem in sysfs driver

From: Jack Rosenthal
Date: Wed Sep 07 2022 - 16:21:59 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.

Write access is provided to all CBMEM regions via
/sys/firmware/coreboot/cbmem/<id>/mem, as the existing cbmem tooling
updates this memory region, and envisioned use cases with crossystem
can benefit from updating memory regions.

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>
---
v10:
* Changed /mem back to read/write support based on offline
conversation with Julius Werner and Stephen Boyd. As noted above,
existing tools make use of writing to these memory regions, so we
should support that.
* Inlined cbmem_entry_setup into cbmem_entry_probe.

.../ABI/testing/sysfs-firmware-coreboot | 49 ++++
drivers/firmware/google/Kconfig | 8 +
drivers/firmware/google/Makefile | 3 +
drivers/firmware/google/cbmem.c | 225 ++++++++++++++++++
drivers/firmware/google/coreboot_table.c | 10 +
drivers/firmware/google/coreboot_table.h | 16 ++
6 files changed, 311 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..c003eb515d0c
--- /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/write 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..835950a14fa6
--- /dev/null
+++ b/drivers/firmware/google/cbmem.c
@@ -0,0 +1,225 @@
+// 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_mem_write(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;
+
+ if (pos < 0 || pos >= bin_attr->size)
+ return -EINVAL;
+ if (count > bin_attr->size - pos)
+ count = bin_attr->size - pos;
+
+ memcpy(entry->mem_file_buf + pos, buf, count);
+ return count;
+}
+
+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_probe(struct coreboot_device *dev)
+{
+ struct cbmem_entry *entry;
+ char *kobj_name;
+ int ret;
+
+ entry = devm_kzalloc(&dev->dev, sizeof(*entry), GFP_KERNEL);
+ if (!entry)
+ return -ENOMEM;
+
+ dev_set_drvdata(&dev->dev, entry);
+ entry->dev = dev;
+ 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 = 0600;
+ entry->mem_file.size = entry->dev->cbmem_entry.entry_size;
+ entry->mem_file.read = cbmem_entry_mem_read;
+ entry->mem_file.write = cbmem_entry_mem_write;
+ 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 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;
};
};
--
2.37.2.789.g6183377224-goog