[PATCH v2 1/2] of/fdt: export fdt blob as /sys/firmware/fdt

[Ard Biesheuvel]

On 11 November 2014 15:42, Grant Likely <grant.likely at linaro.org> wrote:
> On Mon, 10 Nov 2014 19:47:01 +0100
> , Ard Biesheuvel <ard.biesheuvel at linaro.org>
>  wrote:
>> Create a new /sys entry '/sys/firmware/fdt' to export the FDT blob
>> that was passed to the kernel by the bootloader. This allows userland
>> applications such as kexec to access the raw binary. The blob needs to
>> be preserved as early as possible by calling preserve_fdt().
>>
>> The fact that this node does not reside under /sys/firmware/device-tree
>> is deliberate: FDT is also used on arm64 UEFI/ACPI systems to
>> communicate just the UEFI and ACPI entry points, but the FDT is never
>> unflattened and used to configure the system.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>
> On further thought, nak. I want tree modifications to be treated as
> bugs. Do a checksum CRC32 or check. It's simpler and it can be extended
> to us an in-blob CRC when the file format gets upreved to include one.
>

Ah, right, I was under the impression that tree modifications were
expected and allowed.
In that case, yes, let me respin to calculate a CRC early on, and
WARN() if it gets corrupted.

-- 
Ard.


> g.
>
> ---
>
> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> index be16ce2ffd69..adda0a16934f 100644
> --- a/drivers/of/Kconfig
> +++ b/drivers/of/Kconfig
> @@ -23,6 +23,7 @@ config OF_FLATTREE
>         bool
>         select DTC
>         select LIBFDT
> +       select CRC
>
>  config OF_EARLY_FLATTREE
>         bool
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 83a8e1154602..80db46a2eab9 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -10,6 +10,7 @@
>   */
>
>  #include <linux/kernel.h>
> +#include <linux/crc32.h>
>  #include <linux/initrd.h>
>  #include <linux/memblock.h>
>  #include <linux/of.h>
> @@ -420,6 +421,7 @@ int __initdata dt_root_addr_cells;
>  int __initdata dt_root_size_cells;
>
>  void *initial_boot_params;
> +u32 initial_boot_params_crc;
>
>  #ifdef CONFIG_OF_EARLY_FLATTREE
>
> @@ -1003,6 +1005,9 @@ bool __init early_init_dt_verify(void *params)
>
>         /* Setup flat device-tree pointer */
>         initial_boot_params = params;
> +       initial_boot_params_crc = crc32_be(0, params, fdt_totalsize(params));
> +       pr_info("FDT CRC: %x\n", initial_boot_params_crc);
> +
>         return true;
>  }
>
>
>
>
>> ---
>>  drivers/of/fdt.c       | 34 ++++++++++++++++++++++++++++++++++
>>  include/linux/of_fdt.h |  2 ++
>>  2 files changed, 36 insertions(+)
>>
>> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
>> index d1ffca8b34ea..e9ee3d5f7ea4 100644
>> --- a/drivers/of/fdt.c
>> +++ b/drivers/of/fdt.c
>> @@ -22,6 +22,7 @@
>>  #include <linux/libfdt.h>
>>  #include <linux/debugfs.h>
>>  #include <linux/serial_core.h>
>> +#include <linux/sysfs.h>
>>
>>  #include <asm/setup.h>  /* for COMMAND_LINE_SIZE */
>>  #include <asm/page.h>
>> @@ -1103,4 +1104,37 @@ static int __init of_flat_dt_debugfs_export_fdt(void)
>>  module_init(of_flat_dt_debugfs_export_fdt);
>>  #endif
>>
>> +static u8 *raw_fdt_copy;
>> +
>> +void __init preserve_fdt(void)
>> +{
>> +     u32 fdt_size;
>> +
>> +     fdt_size = fdt_totalsize(initial_boot_params);
>> +     raw_fdt_copy = memcpy(__va(memblock_alloc(fdt_size, PAGE_SIZE)),
>> +                           initial_boot_params, fdt_size);
>> +}
>> +
>> +#ifdef CONFIG_SYSFS
>> +static ssize_t of_fdt_raw_read(struct file *filp, struct kobject *kobj,
>> +                            struct bin_attribute *bin_attr,
>> +                            char *buf, loff_t off, size_t count)
>> +{
>> +     memcpy(buf, raw_fdt_copy + off, count);
>> +     return count;
>> +}
>> +
>> +static int __init of_fdt_raw_init(void)
>> +{
>> +     static struct bin_attribute of_fdt_raw_attr =
>> +             __BIN_ATTR(fdt, S_IRUSR, of_fdt_raw_read, NULL, 0);
>> +
>> +     if (!raw_fdt_copy)
>> +             return 0;
>> +     of_fdt_raw_attr.size = fdt_totalsize(raw_fdt_copy);
>> +     return sysfs_create_bin_file(firmware_kobj, &of_fdt_raw_attr);
>> +}
>> +module_init(of_fdt_raw_init);
>> +#endif
>> +
>>  #endif /* CONFIG_OF_EARLY_FLATTREE */
>> diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
>> index 0ff360d5b3b3..7672a26305a5 100644
>> --- a/include/linux/of_fdt.h
>> +++ b/include/linux/of_fdt.h
>> @@ -83,6 +83,7 @@ extern const void *of_flat_dt_match_machine(const void *default_match,
>>  /* Other Prototypes */
>>  extern void unflatten_device_tree(void);
>>  extern void unflatten_and_copy_device_tree(void);
>> +extern void preserve_fdt(void);
>>  extern void early_init_devtree(void *);
>>  extern void early_get_first_memblock_info(void *, phys_addr_t *);
>>  extern u64 fdt_translate_address(const void *blob, int node_offset);
>> @@ -92,6 +93,7 @@ static inline void early_init_fdt_scan_reserved_mem(void) {}
>>  static inline const char *of_flat_dt_get_machine_name(void) { return NULL; }
>>  static inline void unflatten_device_tree(void) {}
>>  static inline void unflatten_and_copy_device_tree(void) {}
>> +static inline void preserve_fdt(void) {}
>>  #endif /* CONFIG_OF_FLATTREE */
>>
>>  #endif /* __ASSEMBLY__ */
>> --
>> 1.8.3.2
>>
>