Re: [PATCH 1/2] firmware: coreboot: Export the binary FMAP

Stephen Boyd
2019-10-08T22:48:03Z

Quoting patrick.rudolph@9elements.com (2019-10-08 04:53:25)
> From: Patrick Rudolph <patrick.rudolph@9elements.com>
>
> Expose coreboot's binary FMAP[1] to /sys/firmware/fmap.
>
> coreboot copies the FMAP to a CBMEM buffer at boot since CB:35377[2],
> allowing an architecture independ way of exposing the FMAP to userspace.
>
> Will be used by fwupd[3] to determine the current firmware layout.
>
> [1]: https://doc.coreboot.org/lib/flashmap.html
> [2]: https://review.coreboot.org/c/coreboot/+/35377
> [3]: https://fwupd.org/
>
> Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
> ---
> drivers/firmware/google/Kconfig | 8 ++
> drivers/firmware/google/Makefile | 1 +
> drivers/firmware/google/fmap-coreboot.c | 156 ++++++++++++++++++++++
> drivers/firmware/google/fmap-coreboot.h | 13 ++
> drivers/firmware/google/fmap_serialized.h | 59 ++++++++
> 5 files changed, 237 insertions(+)
> create mode 100644 drivers/firmware/google/fmap-coreboot.c
> create mode 100644 drivers/firmware/google/fmap-coreboot.h
> create mode 100644 drivers/firmware/google/fmap_serialized.h
>
> diff --git a/drivers/firmware/google/Kconfig b/drivers/firmware/google/Kconfig
> index a3a6ca659ffa..5fbbd7b8fef6 100644
> --- a/drivers/firmware/google/Kconfig
> +++ b/drivers/firmware/google/Kconfig
> @@ -74,4 +74,12 @@ config GOOGLE_VPD
> This option enables the kernel to expose the content of Google VPD
> under /sys/firmware/vpd.
>
> +config GOOGLE_FMAP
> + tristate "Coreboot FMAP access"
> + depends on GOOGLE_COREBOOT_TABLE
> + help
> + This option enables the kernel to search for a Google FMAP in
> + the coreboot table. If found, this binary file is exported to userland
> + in the file /sys/firmware/fmap.
> +
> endif # GOOGLE_FIRMWARE
> diff --git a/drivers/firmware/google/Makefile b/drivers/firmware/google/Makefile
> index d17caded5d88..6d31fe167700 100644
> --- a/drivers/firmware/google/Makefile
> +++ b/drivers/firmware/google/Makefile
> @@ -6,6 +6,7 @@ obj-$(CONFIG_GOOGLE_FRAMEBUFFER_COREBOOT) += framebuffer-coreboot.o
> obj-$(CONFIG_GOOGLE_MEMCONSOLE) += memconsole.o
> obj-$(CONFIG_GOOGLE_MEMCONSOLE_COREBOOT) += memconsole-coreboot.o
> obj-$(CONFIG_GOOGLE_MEMCONSOLE_X86_LEGACY) += memconsole-x86-legacy.o
> +obj-$(CONFIG_GOOGLE_FMAP) += fmap-coreboot.o
>
> vpd-sysfs-y := vpd.o vpd_decode.o
> obj-$(CONFIG_GOOGLE_VPD) += vpd-sysfs.o
> diff --git a/drivers/firmware/google/fmap-coreboot.c b/drivers/firmware/google/fmap-coreboot.c
> new file mode 100644
> index 000000000000..14050030ebc6
> --- /dev/null
> +++ b/drivers/firmware/google/fmap-coreboot.c
> @@ -0,0 +1,156 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * fmap-coreboot.c
> + *
> + * Exports the binary FMAP through coreboot table.
> + *
> + * Copyright 2012-2013 David Herrmann <dh.herrmann@gmail.com>
> + * Copyright 2017 Google Inc.
> + * Copyright 2019 9elements Agency GmbH <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/io.h>
> +
> +#include "coreboot_table.h"
> +#include "fmap_serialized.h"
> +
> +#define CB_TAG_FMAP 0x37
> +
> +static void *fmap;
> +static u32 fmap_size;
> +
> +/*
> + * Convert FMAP region to name.
> + * The caller has to free the string.
> + * Return NULL if no containing region was found.
> + */
> +const char *coreboot_fmap_region_to_name(const u32 start, const u32 size)
> +{
> + const char *name = NULL;
> + struct fmap *iter;
> + u32 size_old = ~0;
> + int i;
> +
> + iter = fmap;
> + /* Find smallest containing region */
> + for (i = 0; i < iter->nareas && fmap; i++) {
> + if (iter->areas[i].offset <= start &&
> + iter->areas[i].size >= size &&
> + iter->areas[i].size <= size_old) {
> + size_old = iter->areas[i].size;
> + name = iter->areas[i].name;
> + }
> + }
> +
> + if (name)
> + return kstrdup(name, GFP_KERNEL);
> + return NULL;
> +}
> +EXPORT_SYMBOL(coreboot_fmap_region_to_name);
> +
> +static ssize_t fmap_read(struct file *filp, struct kobject *kobp,
> + struct bin_attribute *bin_attr, char *buf,
> + loff_t pos, size_t count)
> +{
> + if (!fmap)
> + return -ENODEV;
> +
> + return memory_read_from_buffer(buf, count, &pos, fmap, fmap_size);
> +}
> +
> +static int fmap_probe(struct coreboot_device *dev)
> +{
> + struct lb_cbmem_ref *cbmem_ref = &dev->cbmem_ref;
> + struct fmap *header;
> +
> + if (!cbmem_ref)
> + return -ENODEV;

This is impossible.

> +
> + header = memremap(cbmem_ref->cbmem_addr, sizeof(*header), MEMREMAP_WB);
> + if (!header) {
> + pr_warn("coreboot: Failed to remap FMAP\n");
> + return -ENOMEM;
> + }
> +
> + /* Validate FMAP signature */
> + if (memcmp(header->signature, FMAP_SIGNATURE,
> + sizeof(header->signature))) {
> + pr_warn("coreboot: FMAP signature mismatch\n");
> + memunmap(header);
> + return -ENODEV;
> + }
> +
> + /* Validate FMAP version */
> + if (header->ver_major != FMAP_VER_MAJOR) {
> + pr_warn("coreboot: FMAP version not supported\n");
> + memunmap(header);
> + return -ENODEV;
> + }
> +
> + pr_info("coreboot: Got valid FMAP v%u.%u for 0x%x byte ROM\n",
> + header->ver_major, header->ver_minor, header->size);
> +
> + fmap_size = sizeof(*header) + header->nareas * sizeof(struct fmap_area);
> + memunmap(header);
> +
> + fmap = devm_memremap(&dev->dev, cbmem_ref->cbmem_addr, fmap_size,
> + MEMREMAP_WB);
> + if (!fmap) {
> + pr_warn("coreboot: Failed to remap FMAP\n");
> + return -ENOMEM;
> + }
> +
> + return 0;
> +}
> +
> +static int fmap_remove(struct coreboot_device *dev)
> +{
> + struct platform_device *pdev = dev_get_drvdata(&dev->dev);
> +
> + platform_device_unregister(pdev);
> +
> + return 0;
> +}
> +
> +static struct coreboot_driver fmap_driver = {
> + .probe = fmap_probe,
> + .remove = fmap_remove,
> + .drv = {
> + .name = "fmap",
> + },
> + .tag = CB_TAG_FMAP,
> +};
> +
> +static struct bin_attribute fmap_bin_attr = {
> + .attr = {.name = "fmap", .mode = 0444},
> + .read = fmap_read,
> +};
> +
> +static int __init coreboot_fmap_init(void)
> +{
> + int err;
> +
> + err = sysfs_create_bin_file(firmware_kobj, &fmap_bin_attr);
> + if (err)
> + return err;
> +
> + return coreboot_driver_register(&fmap_driver);
> +}
> +
> +static void coreboot_fmap_exit(void)
> +{
> + coreboot_driver_unregister(&fmap_driver);
> + sysfs_remove_bin_file(firmware_kobj, &fmap_bin_attr);
> +}
> +
> +module_init(coreboot_fmap_init);
> +module_exit(coreboot_fmap_exit);
> +
> +MODULE_AUTHOR("9elements Agency GmbH");
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/firmware/google/fmap-coreboot.h b/drivers/firmware/google/fmap-coreboot.h
> new file mode 100644
> index 000000000000..7107a01af0e3
> --- /dev/null
> +++ b/drivers/firmware/google/fmap-coreboot.h
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * bootmedia-coreboot.h
> + *
> + * Copyright 2019 9elements Agency GmbH <patrick.rudolph@9elements.com>
> + */
> +
> +#ifndef __FMAP_COREBOOT_H
> +#define __FMAP_COREBOOT_H
> +
> +const char *coreboot_fmap_region_to_name(const u32 start, const u32 size);
> +
> +#endif /* __FMAP_COREBOOT_H */
> diff --git a/drivers/firmware/google/fmap_serialized.h b/drivers/firmware/google/fmap_serialized.h
> new file mode 100644
> index 000000000000..a001e47fa244
> --- /dev/null
> +++ b/drivers/firmware/google/fmap_serialized.h
> @@ -0,0 +1,59 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright 2010, Google Inc.
> + * All rights reserved.
> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions are
> + * met:
> + * * Redistributions of source code must retain the above copyright
> + * notice, this list of conditions and the following disclaimer.
> + * * Redistributions in binary form must reproduce the above
> + * copyright notice, this list of conditions and the following disclaimer
> + * in the documentation and/or other materials provided with the
> + * distribution.
> + * * Neither the name of Google Inc. nor the names of its
> + * contributors may be used to endorse or promote products derived from
> + * this software without specific prior written permission.
> + *
> + */
> +
> +#ifndef FLASHMAP_SERIALIZED_H__
> +#define FLASHMAP_SERIALIZED_H__
> +
> +#define FMAP_SIGNATURE "__FMAP__"
> +#define FMAP_VER_MAJOR 1 /* this header's FMAP major version */
> +#define FMAP_VER_MINOR 1 /* this header's FMAP minor version */
> +#define FMAP_STRLEN 32 /* maximum length for strings,
> + * including null-terminator
> + */
> +
> +enum fmap_flags {
> + FMAP_AREA_STATIC = 1 << 0,
> + FMAP_AREA_COMPRESSED = 1 << 1,
> + FMAP_AREA_RO = 1 << 2,
> + FMAP_AREA_PRESERVE = 1 << 3,
> +};
> +
> +/* Mapping of volatile and static regions in firmware binary */
> +struct fmap_area {
> + u32 offset; /* offset relative to base */
> + u32 size; /* size in bytes */
> + u8 name[FMAP_STRLEN]; /* descriptive name */
> + u16 flags; /* flags for this area */
> +} __packed;
> +
> +struct fmap {
> + u8 signature[8]; /* "__FMAP__" (0x5F5F464D41505F5F) */
> + u8 ver_major; /* major version */
> + u8 ver_minor; /* minor version */
> + u64 base; /* address of the firmware binary */
> + u32 size; /* size of firmware binary in bytes */
> + u8 name[FMAP_STRLEN]; /* name of this firmware binary */
> + u16 nareas; /* number of areas described by
> + * fmap_areas[] below
> + */
> + struct fmap_area areas[];
> +} __packed;
> +
> +#endif /* FLASHMAP_SERIALIZED_H__ */
> --
> 2.21.0
>