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

[Grant Likely <grant.likely-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On Mon, 10 Nov 2014 19:47:01 +0100
, Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.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-QSEj5FYQhm4dnm+yROfE0A@public.gmane.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.

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
> 

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