Random number generator fixes for Linux 5.18-rc1.

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Merge tag 'random-5.18-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random

Pull random number generator fixes from Jason Donenfeld:

 - If a hardware random number generator passes a sufficiently large
   chunk of entropy to random.c during early boot, we now skip the
   "fast_init" business and let it initialize the RNG.

   This makes CONFIG_RANDOM_TRUST_BOOTLOADER=y actually useful.

 - We already have the command line `random.trust_cpu=0/1` option for
   RDRAND, which let distros enable CONFIG_RANDOM_TRUST_CPU=y while
   placating concerns of more paranoid users.

   Now we add `random.trust_bootloader=0/1` so that distros can
   similarly enable CONFIG_RANDOM_TRUST_BOOTLOADER=y.

 - Re-add a comment that got removed by accident in the recent revert.

 - Add the spec-compliant ACPI CID for vmgenid, which Microsoft added to
   the vmgenid spec at Ard's request during earlier review.

 - Restore build-time randomness via the latent entropy plugin, which
   was lost when we transitioned to using a hash function.

* tag 'random-5.18-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random:
  random: mix build-time latent entropy into pool at init
  virt: vmgenid: recognize new CID added by Hyper-V
  random: re-add removed comment about get_random_{u32,u64} reseeding
  random: treat bootloader trust toggle the same way as cpu trust toggle
  random: skip fast_init if hwrng provides large chunk of entropy

Documentation/admin-guide/kernel-parameters.txt

@@ -4427,6 +4427,12 @@
 			fully seed the kernel's CRNG. Default is controlled
 			by CONFIG_RANDOM_TRUST_CPU.
 
+	random.trust_bootloader={on,off}
+			[KNL] Enable or disable trusting the use of a
+			seed passed by the bootloader (if available) to
+			fully seed the kernel's CRNG. Default is controlled
+			by CONFIG_RANDOM_TRUST_BOOTLOADER.
+
 	randomize_kstack_offset=
 			[KNL] Enable or disable kernel stack offset
 			randomization, which provides roughly 5 bits of

drivers/char/Kconfig

@@ -449,6 +449,7 @@ config RANDOM_TRUST_BOOTLOADER
 	device randomness. Say Y here to assume the entropy provided by the
 	booloader is trustworthy so it will be added to the kernel's entropy
 	pool. Otherwise, say N here so it will be regarded as device input that
-	only mixes the entropy pool.
+	only mixes the entropy pool. This can also be configured at boot with
+	"random.trust_bootloader=on/off".
 
 endmenu

drivers/char/random.c

@@ -224,9 +224,10 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller, void
  *
  * These interfaces will return the requested number of random bytes
  * into the given buffer or as a return value. This is equivalent to
- * a read from /dev/urandom. The integer family of functions may be
- * higher performance for one-off random integers, because they do a
- * bit of buffering.
+ * a read from /dev/urandom. The u32, u64, int, and long family of
+ * functions may be higher performance for one-off random integers,
+ * because they do a bit of buffering and do not invoke reseeding
+ * until the buffer is emptied.
  *
  *********************************************************************/
 
@@ -948,11 +949,17 @@ static bool drain_entropy(void *buf, size_t nbytes, bool force)
  **********************************************************************/
 
 static bool trust_cpu __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_CPU);
+static bool trust_bootloader __ro_after_init = IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER);
 static int __init parse_trust_cpu(char *arg)
 {
 	return kstrtobool(arg, &trust_cpu);
 }
+static int __init parse_trust_bootloader(char *arg)
+{
+	return kstrtobool(arg, &trust_bootloader);
+}
 early_param("random.trust_cpu", parse_trust_cpu);
+early_param("random.trust_bootloader", parse_trust_bootloader);
 
 /*
  * The first collection of entropy occurs at system boot while interrupts
@@ -968,6 +975,11 @@ int __init rand_initialize(void)
 	bool arch_init = true;
 	unsigned long rv;
 
+#if defined(LATENT_ENTROPY_PLUGIN)
+	static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
+	_mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
+#endif
+
 	for (i = 0; i < BLAKE2S_BLOCK_SIZE; i += sizeof(rv)) {
 		if (!arch_get_random_seed_long_early(&rv) &&
 		    !arch_get_random_long_early(&rv)) {
@@ -1128,7 +1140,7 @@ void rand_initialize_disk(struct gendisk *disk)
 void add_hwgenerator_randomness(const void *buffer, size_t count,
 				size_t entropy)
 {
-	if (unlikely(crng_init == 0)) {
+	if (unlikely(crng_init == 0 && entropy < POOL_MIN_BITS)) {
 		size_t ret = crng_pre_init_inject(buffer, count, true);
 		mix_pool_bytes(buffer, ret);
 		count -= ret;
@@ -1160,7 +1172,7 @@ EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
  */
 void add_bootloader_randomness(const void *buf, size_t size)
 {
-	if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
+	if (trust_bootloader)
 		add_hwgenerator_randomness(buf, size, size * 8);
 	else
 		add_device_randomness(buf, size);

drivers/virt/vmgenid.c

@@ -78,6 +78,7 @@ static void vmgenid_notify(struct acpi_device *device, u32 event)
 }
 
 static const struct acpi_device_id vmgenid_ids[] = {
+	{ "VMGENCTR", 0 },
 	{ "VM_GEN_COUNTER", 0 },
 	{ }
 };