5 files changed, 175 insertions, 1 deletions

diff --git a/drivers/firmware/google/Kconfig b/drivers/firmware/google/Kconfig
index 983e07dc022e..9f190eab43ed 100644
--- a/drivers/firmware/google/Kconfig
+++ b/drivers/firmware/google/Kconfig
@@ -19,6 +19,21 @@ 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
+	  CBMEM is a downwards-growing memory region created by the
+	  Coreboot BIOS containing tagged data structures from the
+	  BIOS.  These data structures expose things like the verified
+	  boot firmware variables, flash layout, firmware event log,
+	  and more.
+
+	  This option enables the cbmem module, which causes the
+	  kernel to search for Coreboot CBMEM entries, and expose the
+	  memory for each entry in sysfs under
+	  /sys/bus/coreboot/devices/cbmem-<id>.
+
 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..685f3070ce9d
--- /dev/null
+++ b/drivers/firmware/google/cbmem.c
@@ -0,0 +1,129 @@
+// 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"
+
+struct cbmem_entry {
+	char *mem_file_buf;
+	u32 size;
+};
+
+static struct cbmem_entry *to_cbmem_entry(struct kobject *kobj)
+{
+	return dev_get_drvdata(kobj_to_dev(kobj));
+}
+
+static ssize_t mem_read(struct file *filp, struct kobject *kobj,
+			struct bin_attribute *bin_attr, char *buf, loff_t pos,
+			size_t count)
+{
+	struct cbmem_entry *entry = to_cbmem_entry(kobj);
+
+	return memory_read_from_buffer(buf, count, &pos, entry->mem_file_buf,
+				       entry->size);
+}
+
+static ssize_t mem_write(struct file *filp, struct kobject *kobj,
+			 struct bin_attribute *bin_attr, char *buf, loff_t pos,
+			 size_t count)
+{
+	struct cbmem_entry *entry = to_cbmem_entry(kobj);
+
+	if (pos < 0 || pos >= entry->size)
+		return -EINVAL;
+	if (count > entry->size - pos)
+		count = entry->size - pos;
+
+	memcpy(entry->mem_file_buf + pos, buf, count);
+	return count;
+}
+static BIN_ATTR_ADMIN_RW(mem, 0);
+
+static ssize_t address_show(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	struct coreboot_device *cbdev = dev_to_coreboot_device(dev);
+
+	return sysfs_emit(buf, "0x%llx\n", cbdev->cbmem_entry.address);
+}
+static DEVICE_ATTR_RO(address);
+
+static ssize_t size_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	struct coreboot_device *cbdev = dev_to_coreboot_device(dev);
+
+	return sysfs_emit(buf, "0x%x\n", cbdev->cbmem_entry.entry_size);
+}
+static DEVICE_ATTR_RO(size);
+
+static struct attribute *attrs[] = {
+	&dev_attr_address.attr,
+	&dev_attr_size.attr,
+	NULL,
+};
+
+static struct bin_attribute *bin_attrs[] = {
+	&bin_attr_mem,
+	NULL,
+};
+
+static const struct attribute_group cbmem_entry_group = {
+	.attrs = attrs,
+	.bin_attrs = bin_attrs,
+};
+
+static const struct attribute_group *dev_groups[] = {
+	&cbmem_entry_group,
+	NULL,
+};
+
+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->mem_file_buf = devm_memremap(&dev->dev, dev->cbmem_entry.address,
+					    dev->cbmem_entry.entry_size,
+					    MEMREMAP_WB);
+	if (!entry->mem_file_buf)
+		return -ENOMEM;
+
+	entry->size = dev->cbmem_entry.entry_size;
+
+	return 0;
+}
+
+static struct coreboot_driver cbmem_entry_driver = {
+	.probe = cbmem_entry_probe,
+	.drv = {
+		.name = "cbmem",
+		.owner = THIS_MODULE,
+		.dev_groups = dev_groups,
+	},
+	.tag = LB_TAG_CBMEM_ENTRY,
+};
+module_coreboot_driver(cbmem_entry_driver);
+
+MODULE_AUTHOR("Jack Rosenthal <jrosenth@chromium.org>");
+MODULE_LICENSE("GPL");
diff --git a/drivers/firmware/google/coreboot_table.c b/drivers/firmware/google/coreboot_table.c
index c52bcaa9def6..7748067eb9e6 100644
--- a/drivers/firmware/google/coreboot_table.c
+++ b/drivers/firmware/google/coreboot_table.c
@@ -97,12 +97,21 @@ static int coreboot_table_populate(struct device *dev, void *ptr)
 		if (!device)
 			return -ENOMEM;
 
-		dev_set_name(&device->dev, "coreboot%d", i);
 		device->dev.parent = dev;
 		device->dev.bus = &coreboot_bus_type;
 		device->dev.release = coreboot_device_release;
 		memcpy(&device->entry, ptr_entry, entry->size);
 
+		switch (device->entry.tag) {
+		case LB_TAG_CBMEM_ENTRY:
+			dev_set_name(&device->dev, "cbmem-%08x",
+				     device->cbmem_entry.id);
+			break;
+		default:
+			dev_set_name(&device->dev, "coreboot%d", i);
+			break;
+		}
+
 		ret = device_register(&device->dev);
 		if (ret) {
 			put_device(&device->dev);
diff --git a/drivers/firmware/google/coreboot_table.h b/drivers/firmware/google/coreboot_table.h
index beb778674acd..37f4d335a606 100644
--- a/drivers/firmware/google/coreboot_table.h
+++ b/drivers/firmware/google/coreboot_table.h
@@ -39,6 +39,18 @@ struct lb_cbmem_ref {
 	u64 cbmem_addr;
 };
 
+#define LB_TAG_CBMEM_ENTRY 0x31
+
+/* 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;
@@ -65,10 +77,16 @@ 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;
 	};
 };
 
+static inline struct coreboot_device *dev_to_coreboot_device(struct device *dev)
+{
+	return container_of(dev, struct coreboot_device, dev);
+}
+
 /* A driver for handling devices described in coreboot tables. */
 struct coreboot_driver {
 	int (*probe)(struct coreboot_device *);