Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 9b254366 authored by Kees Cook's avatar Kees Cook Committed by Theodore Ts'o
Browse files

random: make CPU trust a boot parameter 



Instead of forcing a distro or other system builder to choose
at build time whether the CPU is trusted for CRNG seeding via
CONFIG_RANDOM_TRUST_CPU, provide a boot-time parameter for end users to
control the choice. The CONFIG will set the default state instead.

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 9a47249d

Documentation/admin-guide/kernel-parameters.txt

+6 −0
Original line number Diff line number Diff line
@@ -3390,6 +3390,12 @@ 
	ramdisk_size=	[RAM] Sizes of RAM disks in kilobytes

			See Documentation/blockdev/ramdisk.txt.



	random.trust_cpu={on,off}

			[KNL] Enable or disable trusting the use of the

			CPU's random number generator (if available) to

			fully seed the kernel's CRNG. Default is controlled

			by CONFIG_RANDOM_TRUST_CPU.



	ras=option[,option,...]	[KNL] RAS-specific options



		cec_disable	[X86]

drivers/char/Kconfig

+2 −2
Original line number Diff line number Diff line
@@ -566,5 +566,5 @@ config RANDOM_TRUST_CPU 
	that CPU manufacturer (perhaps with the insistence or mandate

	of a Nation State's intelligence or law enforcement agencies)

	has not installed a hidden back door to compromise the CPU's

	random number generation facilities.

	random number generation facilities. This can also be configured

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

drivers/char/random.c

+8 −3
Original line number Diff line number Diff line
@@ -779,6 +779,13 @@ static struct crng_state **crng_node_pool __read_mostly; 


static void invalidate_batched_entropy(void);



static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);

static int __init parse_trust_cpu(char *arg)

{

	return kstrtobool(arg, &trust_cpu);

}

early_param("random.trust_cpu", parse_trust_cpu);



static void crng_initialize(struct crng_state *crng)

{

	int		i;
@@ -799,12 +806,10 @@ static void crng_initialize(struct crng_state *crng) 
		}

		crng->state[i] ^= rv;

	}

#ifdef CONFIG_RANDOM_TRUST_CPU

	if (arch_init) {

	if (trust_cpu && arch_init) {

		crng_init = 2;

		pr_notice("random: crng done (trusting CPU's manufacturer)\n");

	}

#endif

	crng->init_time = jiffies - CRNG_RESEED_INTERVAL - 1;

}