diff --git a/Documentation/ABI/testing/sysfs-bus-coreboot b/Documentation/ABI/testing/sysfs-bus-coreboot new file mode 100644 index 000000000000..9c5accecc470 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-bus-coreboot @@ -0,0 +1,45 @@ +What: /sys/bus/coreboot +Date: August 2022 +Contact: Jack Rosenthal +Description: + The coreboot bus provides a variety of virtual devices used to + access data structures created by the Coreboot BIOS. + +What: /sys/bus/coreboot/devices/cbmem- +Date: August 2022 +Contact: Jack Rosenthal +Description: + CBMEM is a downwards-growing memory region created by Coreboot, + and contains tagged data structures to be shared with payloads + in the boot process and the OS. Each CBMEM entry is given a + directory in /sys/bus/coreboot/devices based on its id. + 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/bus/coreboot/devices/cbmem-/address +Date: August 2022 +Contact: Jack Rosenthal +Description: + This is the pyhsical memory address that the CBMEM entry's data + begins at, in hexadecimal (e.g., ``0x76ffe000``). + +What: /sys/bus/coreboot/devices/cbmem-/size +Date: August 2022 +Contact: Jack Rosenthal +Description: + This is the size of the CBMEM entry's data, in hexadecimal + (e.g., ``0x1234``). + +What: /sys/bus/coreboot/devices/cbmem-/mem +Date: August 2022 +Contact: Jack Rosenthal +Description: + A file exposing read/write access to the entry's data. Note + that this file does not support mmap(), as coreboot + does not guarantee that the data will be page-aligned. + + The mode of this file is 0600. While there shouldn't be + anything security-sensitive contained in CBMEM, read access + requires root privileges given this is exposing a small subset + of physical memory. 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-. + 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 +#include +#include +#include +#include +#include +#include +#include +#include + +#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 "); +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 *);