@@ -80,4 +80,15 @@ config LRNG_KCAPI
provided by the selected kernel crypto API RNG.
endif # LRNG_DRNG_SWITCH
+config LRNG_JENT
+ bool "Enable Jitter RNG as LRNG Seed Source"
+ select CRYPTO_JITTERENTROPY
+ help
+ The Linux RNG may use the Jitter RNG as noise source. Enabling
+ this option enables the use of the Jitter RNG. Its default
+ entropy level is 16 bits of entropy per 256 data bits delivered
+ by the Jitter RNG. This entropy level can be changed at boot
+ time or at runtime with the lrng_base.jitterrng configuration
+ variable.
+
endif # LRNG
@@ -13,3 +13,4 @@ obj-$(CONFIG_SYSCTL) += lrng_proc.o
obj-$(CONFIG_LRNG_DRNG_SWITCH) += lrng_switch.o
obj-$(CONFIG_LRNG_DRBG) += lrng_drbg.o
obj-$(CONFIG_LRNG_KCAPI) += lrng_kcapi.o
+obj-$(CONFIG_LRNG_JENT) += lrng_jent.o
new file mode 100644
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * LRNG Fast Noise Source: Jitter RNG
+ *
+ * Copyright (C) 2016 - 2019, Stephan Mueller <smueller@chronox.de>
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include "lrng_internal.h"
+
+/*
+ * Estimated entropy of data is a 16th of LRNG_DRNG_SECURITY_STRENGTH_BITS.
+ * Albeit a full entropy assessment is provided for the noise source indicating
+ * that it provides high entropy rates and considering that it deactivates
+ * when it detects insufficient hardware, the chosen under estimation of
+ * entropy is considered to be acceptable to all reviewers.
+ */
+static u32 jitterrng = LRNG_DRNG_SECURITY_STRENGTH_BITS>>4;
+module_param(jitterrng, uint, 0644);
+MODULE_PARM_DESC(jitterrng, "Entropy in bits of 256 data bits from Jitter "
+ "RNG noise source");
+
+/**
+ * Get Jitter RNG entropy
+ *
+ * @outbuf buffer to store entropy
+ * @outbuflen length of buffer
+ * @return > 0 on success where value provides the added entropy in bits
+ * 0 if no fast source was available
+ */
+struct rand_data;
+struct rand_data *jent_lrng_entropy_collector(void);
+int jent_read_entropy(struct rand_data *ec, unsigned char *data,
+ unsigned int len);
+static struct rand_data *lrng_jent_state;
+
+u32 lrng_get_jent(u8 *outbuf, unsigned int outbuflen)
+{
+ int ret;
+ u32 ent_bits = jitterrng;
+ unsigned long flags;
+ static DEFINE_SPINLOCK(lrng_jent_lock);
+ static int lrng_jent_initialized = 0;
+
+ spin_lock_irqsave(&lrng_jent_lock, flags);
+
+ if (!ent_bits || (lrng_jent_initialized == -1)) {
+ spin_unlock_irqrestore(&lrng_jent_lock, flags);
+ return 0;
+ }
+
+ if (!lrng_jent_initialized) {
+ lrng_jent_state = jent_lrng_entropy_collector();
+ if (!lrng_jent_state) {
+ jitterrng = 0;
+ lrng_jent_initialized = -1;
+ spin_unlock_irqrestore(&lrng_jent_lock, flags);
+ pr_info("Jitter RNG unusable on current system\n");
+ return 0;
+ }
+ lrng_jent_initialized = 1;
+ pr_debug("Jitter RNG working on current system\n");
+ }
+ ret = jent_read_entropy(lrng_jent_state, outbuf, outbuflen);
+ spin_unlock_irqrestore(&lrng_jent_lock, flags);
+
+ if (ret) {
+ pr_debug("Jitter RNG failed with %d\n", ret);
+ return 0;
+ }
+
+ /* Obtain entropy statement */
+ if (outbuflen != LRNG_DRNG_SECURITY_STRENGTH_BYTES)
+ ent_bits = (ent_bits * outbuflen<<3) /
+ LRNG_DRNG_SECURITY_STRENGTH_BITS;
+ /* Cap entropy to buffer size in bits */
+ ent_bits = min_t(u32, ent_bits, outbuflen<<3);
+ pr_debug("obtained %u bits of entropy from Jitter RNG noise source\n",
+ ent_bits);
+
+ return ent_bits;
+}
+
+u32 lrng_jent_entropylevel(void)
+{
+ return min_t(u32, jitterrng, LRNG_DRNG_SECURITY_STRENGTH_BITS);
+}