@@ -23,6 +23,7 @@ config OF_FLATTREE
bool
select DTC
select LIBFDT
+ select CRC32
config OF_EARLY_FLATTREE
bool
@@ -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 +1116,27 @@ 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 (WARN(of_fdt_crc32 != of_fdt_get_crc32(initial_boot_params),
+ "CRC check failed on binary FDT"))
+ return -EFAULT;
+ 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 */
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@linaro.org> --- v3: keep checksum instead of copying the entire blob, and WARN on mismatch drivers/of/Kconfig | 1 + drivers/of/fdt.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 37 insertions(+)