Merge tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull random driver fix from Ted Ts'o:
 "Fix things so the choice of whether or not to trust RDRAND to
  initialize the CRNG is configurable via the boot option
  random.trust_cpu={on,off}"

* tag 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  random: make CPU trust a boot parameter

3 files changed, 16 insertions, 5 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9871e649ffef..64a3bf54b974 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3523,6 +3523,12 @@
         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;
 }