From: Kees Cook keescook@chromium.org
commit 9b25436662d5fb4c66eb527ead53cab15f596ee0 upstream.
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 Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Documentation/admin-guide/kernel-parameters.txt | 6 ++++++ drivers/char/Kconfig | 4 ++-- drivers/char/random.c | 11 ++++++++--- 3 files changed, 16 insertions(+), 5 deletions(-)
--- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3526,6 +3526,12 @@ 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] --- a/drivers/char/Kconfig +++ b/drivers/char/Kconfig @@ -602,5 +602,5 @@ 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". --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -779,6 +779,13 @@ static struct crng_state **crng_node_poo
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_ } 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; }