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random: make CPU trust a boot parameter

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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: Kees Cook <keescook@chromium.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Kees Cook 2018-08-27 14:51:54 -07:00 committed by Theodore Ts'o
parent 9a47249d44
commit 9b25436662
3 changed files with 16 additions and 5 deletions
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6
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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]

4
drivers/char/Kconfig
View File

@ -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".

11
drivers/char/random.c
View File

@ -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;
}