[PATCH v4] of/fdt: export fdt blob as /sys/firmware/fdt

[Grant Likely]

On Wed, 12 Nov 2014 13:28:28 +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 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.
> 
> A CRC32 checksum is calculated over the entire FDT blob, and verified
> at late_initcall time. The sysfs entry is instantiated only if the
> checksum is valid, i.e., if the FDT blob has not been modified in the
> mean time. Otherwise, a warning is printed.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>

Looks good to me. Merged, thanks.

g.

> ---
> v4: use pr_warn() instead of WARN()
> v3: keep checksum instead of copying the entire blob, and WARN on mismatch
> 
>  drivers/of/Kconfig |  1 +
>  drivers/of/fdt.c   | 37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> index 1a13f5b722c5..0348c208343c 100644
> --- a/drivers/of/Kconfig
> +++ b/drivers/of/Kconfig
> @@ -23,6 +23,7 @@ config OF_FLATTREE
>  	bool
>  	select DTC
>  	select LIBFDT
> +	select CRC32
>  
>  config OF_EARLY_FLATTREE
>  	bool
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index d1ffca8b34ea..0004871ebccf 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -9,6 +9,7 @@
>   * version 2 as published by the Free Software Foundation.
>   */
>  
> +#include <linux/crc32.h>
>  #include <linux/kernel.h>
>  #include <linux/initrd.h>
>  #include <linux/memblock.h>
> @@ -22,10 +23,20 @@
>  #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>
>  
> +static u32 of_fdt_crc32;
> +
> +static u32 of_fdt_get_crc32(void *fdt)
> +{
> +	static u32 const OF_FDT_CRC32_SEED = 0x04c11db7;
> +
> +	return crc32_be(OF_FDT_CRC32_SEED, fdt, fdt_totalsize(fdt));
> +}
> +
>  /*
>   * of_fdt_limit_memory - limit the number of regions in the /memory node
>   * @limit: maximum entries
> @@ -1003,6 +1014,8 @@ bool __init early_init_dt_verify(void *params)
>  		return false;
>  	}
>  
> +	of_fdt_crc32 = of_fdt_get_crc32(initial_boot_params);
> +
>  	return true;
>  }
>  
> @@ -1103,4 +1116,28 @@ static int __init of_flat_dt_debugfs_export_fdt(void)
>  module_init(of_flat_dt_debugfs_export_fdt);
>  #endif
>  
> +#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, initial_boot_params + 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 (of_fdt_crc32 != of_fdt_get_crc32(initial_boot_params)) {
> +		pr_warn("fdt: not creating '/sys/firmware/fdt': CRC check failed");
> +		return 0;
> +	}
> +	of_fdt_raw_attr.size = fdt_totalsize(initial_boot_params);
> +	return sysfs_create_bin_file(firmware_kobj, &of_fdt_raw_attr);
> +}
> +late_initcall(of_fdt_raw_init);
> +#endif
> +
>  #endif /* CONFIG_OF_EARLY_FLATTREE */
> -- 
> 1.8.3.2
>