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authorKees Cook <keescook@chromium.org>2018-08-27 14:51:54 -0700
committerTheodore Ts'o <tytso@mit.edu>2018-09-01 12:51:54 -0400
commit9b25436662d5fb4c66eb527ead53cab15f596ee0 (patch)
treef81de29079d0cd3e4816cae947a0a3b0b3c4767a
parent9a47249d444d344051c7c0e909fad0e88515a5c2 (diff)
downloadlinux-9b25436662d5fb4c66eb527ead53cab15f596ee0.tar.bz2
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: Kees Cook <keescook@chromium.org> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt6
-rw-r--r--drivers/char/Kconfig4
-rw-r--r--drivers/char/random.c11
3 files changed, 16 insertions, 5 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0c8f7889efa1..227c5c6fa4c1 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -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]
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index ce277ee0a28a..40728491f37b 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -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".
diff --git a/drivers/char/random.c b/drivers/char/random.c
index bf5f99fc36f1..c75b6cdf0053 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -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;
}