[PATCH v4] of/fdt: export fdt blob as /sys/firmware/fdt
From: Grant Likely <hidden>
Date: 2014-11-12 16:59:35
Also in:
linux-devicetree
Subsystem:
open firmware and flattened device tree, the rest · Maintainers:
Rob Herring, Saravana Kannan, Linus Torvalds
Possibly related (same subject, not in this thread)
- 2014-11-13 · Re: [PATCH v4] of/fdt: export fdt blob as /sys/firmware/fdt · Ard Biesheuvel <hidden>
- 2014-11-12 · Re: [PATCH v4] of/fdt: export fdt blob as /sys/firmware/fdt · Rob Herring <hidden>
- 2014-11-12 · Re: [PATCH v4] of/fdt: export fdt blob as /sys/firmware/fdt · Grant Likely <hidden>
- 2014-11-12 · [PATCH v4] of/fdt: export fdt blob as /sys/firmware/fdt · Ard Biesheuvel <hidden>
On Wed, 12 Nov 2014 13:28:28 +0100 , Ard Biesheuvel [off-list ref] 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 <redacted>
Actually, I made a couple of changes when I merged it. I removed the older debugfs interface since it overlaps, and I added tests for initial_boot_params to make sure it doesn't try to run on an invalid FDT:
diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
index be16ce2ffd69..fbe8f8d418f7 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 83a8e1154602..c7997e87b4b5 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 +1014,7 @@ bool __init early_init_dt_verify(void *params) /* Setup flat device-tree pointer */ initial_boot_params = params; + of_fdt_crc32 = of_fdt_get_crc32(initial_boot_params); return true; }
@@ -1080,27 +1092,31 @@ void __init unflatten_and_copy_device_tree(void) unflatten_device_tree(); } -#if defined(CONFIG_DEBUG_FS) && defined(DEBUG) -static struct debugfs_blob_wrapper flat_dt_blob; - -static int __init of_flat_dt_debugfs_export_fdt(void) +#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) { - struct dentry *d = debugfs_create_dir("device-tree", NULL); - - if (!d) - return -ENOENT; + memcpy(buf, initial_boot_params + off, count); + return count; +} - flat_dt_blob.data = initial_boot_params; - flat_dt_blob.size = fdt_totalsize(initial_boot_params); +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); - d = debugfs_create_blob("flat-device-tree", S_IFREG | S_IRUSR, - d, &flat_dt_blob); - if (!d) - return -ENOENT; + if (!initial_boot_params || fdt_check_header(initial_boot_params)) + return 0; - return 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); } -module_init(of_flat_dt_debugfs_export_fdt); +late_initcall(of_fdt_raw_init); #endif #endif /* CONFIG_OF_EARLY_FLATTREE */
g.