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Commit 428826f5 authored by Hsin-Yi Wang's avatar Hsin-Yi Wang Committed by Will Deacon
Browse files

fdt: add support for rng-seed 



Introducing a chosen node, rng-seed, which is an entropy that can be
passed to kernel called very early to increase initial device
randomness. Bootloader should provide this entropy and the value is
read from /chosen/rng-seed in DT.

Obtain of_fdt_crc32 for CRC check after early_init_dt_scan_nodes(),
since early_init_dt_scan_chosen() would modify fdt to erase rng-seed.

Add a new interface add_bootloader_randomness() for rng-seed use case.
Depends on whether the seed is trustworthy, rng seed would be passed to
add_hwgenerator_randomness(). Otherwise it would be passed to
add_device_randomness(). Decision is controlled by kernel config
RANDOM_TRUST_BOOTLOADER.

Signed-off-by: default avatarHsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: default avatarStephen Boyd <swboyd@chromium.org>
Reviewed-by: default avatarRob Herring <robh@kernel.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu> # drivers/char/random.c
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent e112b032

drivers/char/Kconfig

+9 −0
Original line number Diff line number Diff line
@@ -573,3 +573,12 @@ config RANDOM_TRUST_CPU 
	has not installed a hidden back door to compromise the CPU's

	random number generation facilities. This can also be configured

	at boot with "random.trust_cpu=on/off".



config RANDOM_TRUST_BOOTLOADER

	bool "Trust the bootloader to initialize Linux's CRNG"

	help

	Some bootloaders can provide entropy to increase the kernel's initial

	device randomness. Say Y here to assume the entropy provided by the

	booloader is trustworthy so it will be added to the kernel's entropy

	pool. Otherwise, say N here so it will be regarded as device input that

	only mixes the entropy pool.
 
 No newline at end of file

drivers/char/random.c

+14 −0
Original line number Diff line number Diff line
@@ -2445,3 +2445,17 @@ void add_hwgenerator_randomness(const char *buffer, size_t count, 
	credit_entropy_bits(poolp, entropy);

}

EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);



/* Handle random seed passed by bootloader.

 * If the seed is trustworthy, it would be regarded as hardware RNGs. Otherwise

 * it would be regarded as device data.

 * The decision is controlled by CONFIG_RANDOM_TRUST_BOOTLOADER.

 */

void add_bootloader_randomness(const void *buf, unsigned int size)

{

	if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))

		add_hwgenerator_randomness(buf, size, size * 8);

	else

		add_device_randomness(buf, size);

}

EXPORT_SYMBOL_GPL(add_bootloader_randomness);
 
 No newline at end of file

drivers/of/fdt.c

+12 −2
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ 
#include <linux/debugfs.h>

#include <linux/serial_core.h>

#include <linux/sysfs.h>

#include <linux/random.h>



#include <asm/setup.h>  /* for COMMAND_LINE_SIZE */

#include <asm/page.h>
@@ -1044,6 +1045,7 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, 
{

	int l;

	const char *p;

	const void *rng_seed;



	pr_debug("search \"chosen\", depth: %d, uname: %s\n", depth, uname);
@@ -1078,6 +1080,14 @@ int __init early_init_dt_scan_chosen(unsigned long node, const char *uname, 


	pr_debug("Command line is: %s\n", (char*)data);



	rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l);

	if (rng_seed && l > 0) {

		add_bootloader_randomness(rng_seed, l);



		/* try to clear seed so it won't be found. */

		fdt_nop_property(initial_boot_params, node, "rng-seed");

	}



	/* break now */

	return 1;

}
@@ -1166,8 +1176,6 @@ bool __init early_init_dt_verify(void *params) 


	/* Setup flat device-tree pointer */

	initial_boot_params = params;

	of_fdt_crc32 = crc32_be(~0, initial_boot_params,

				fdt_totalsize(initial_boot_params));

	return true;

}
@@ -1197,6 +1205,8 @@ bool __init early_init_dt_scan(void *params) 
		return false;



	early_init_dt_scan_nodes();

	of_fdt_crc32 = crc32_be(~0, initial_boot_params,

				fdt_totalsize(initial_boot_params));

	return true;

}

include/linux/random.h

+1 −0
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ struct random_ready_callback { 
};



extern void add_device_randomness(const void *, unsigned int);

extern void add_bootloader_randomness(const void *, unsigned int);



#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)

static inline void add_latent_entropy(void)