[PATCH 0/3] crypto: jitter - Offer compile-time options

[PATCH 0/3] crypto: jitter - Offer compile-time options

[Stephan Müller]

Hi,

the following patchset offers a set of compile-time options to
accommodate different hardware with different entropy rates implied
in their timers. This allows configuring the Jitter RNG in systems
which exhibits insufficient entropy with the default parameters. The
default parameters defined by the patches, however, are identical to
the existing code and thus do not alter the Jitter RNG behavior.

The first patch sets the state by allowing the configuration of
different oversampling rates. The second patch allows the configuration
of different memory sizes and the third allows the configuration
of differnet oversampling rates.

The update of the power up test with the first patch also addresses
reports that the Jitter RNG did not initialize due to it detected
insufficient entropy.

Stephan Mueller (3):
  crypto: jitter - add RCT/APT support for different OSRs
  crypto: jitter - Allow configuration of memory size
  crypto: jitter - Allow configuration of oversampling rate

 crypto/Kconfig               |  60 +++++++++
 crypto/jitterentropy-kcapi.c |  17 ++-
 crypto/jitterentropy.c       | 249 ++++++++++++++++++-----------------
 crypto/jitterentropy.h       |   5 +-
 4 files changed, 207 insertions(+), 124 deletions(-)

-- 
2.42.0

[PATCH 1/3] crypto: jitter - add RCT/APT support for different OSRs

[Stephan Müller]

The oversampling rate (OSR) value specifies the heuristically implied
entropy in the recorded data - H_submitter = 1/osr. A different entropy
estimate implies a different APT/RCT cutoff value. This change adds
support for OSRs 1 through 15. This OSR can be selected by the caller
of the Jitter RNG.

For this patch, the caller still uses one hard-coded OSR. A subsequent
patch allows this value to be configured.

In addition, the power-up self test is adjusted as follows:

* It allows the caller to provide an oversampling rate that should be
tested with - commonly it should be the same as used for the actual
runtime operation. This makes the power-up testing therefore consistent
with the runtime operation.

* It calls now jent_measure_jitter (i.e. collects the full entropy
that can possibly be harvested by the Jitter RNG) instead of only
jent_condition_data (which only returns the entropy harvested from
the conditioning component). This should now alleviate reports where
the Jitter RNG initialization thinks there is too little entropy.

* The power-up test now solely relies on the (enhanced) APT and RCT
test that is used as a health test at runtime.

The code allowing the different OSRs as well as the power-up test
changes are present in the user space version of the Jitter RNG 3.4.1
and thus was already in production use for some time.

Reported-by "Ospan, Abylay" <aospan@amazon.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 crypto/jitterentropy-kcapi.c |   4 +-
 crypto/jitterentropy.c       | 233 ++++++++++++++++++-----------------
 crypto/jitterentropy.h       |   3 +-
 3 files changed, 123 insertions(+), 117 deletions(-)

diff --git a/crypto/jitterentropy-kcapi.c b/crypto/jitterentropy-kcapi.c
index 7d1463a1562a..1de730f94683 100644
--- a/crypto/jitterentropy-kcapi.c
+++ b/crypto/jitterentropy-kcapi.c
@@ -245,7 +245,7 @@ static int jent_kcapi_init(struct crypto_tfm *tfm)
 	crypto_shash_init(sdesc);
 	rng->sdesc = sdesc;
 
-	rng->entropy_collector = jent_entropy_collector_alloc(1, 0, sdesc);
+	rng->entropy_collector = jent_entropy_collector_alloc(0, 0, sdesc);
 	if (!rng->entropy_collector) {
 		ret = -ENOMEM;
 		goto err;
@@ -334,7 +334,7 @@ static int __init jent_mod_init(void)
 
 	desc->tfm = tfm;
 	crypto_shash_init(desc);
-	ret = jent_entropy_init(desc);
+	ret = jent_entropy_init(0, 0, desc);
 	shash_desc_zero(desc);
 	crypto_free_shash(tfm);
 	if (ret) {
diff --git a/crypto/jitterentropy.c b/crypto/jitterentropy.c
index fe9c233ec769..c99734af82b8 100644
--- a/crypto/jitterentropy.c
+++ b/crypto/jitterentropy.c
@@ -72,6 +72,8 @@ struct rand_data {
 	__u64 prev_time;		/* SENSITIVE Previous time stamp */
 	__u64 last_delta;		/* SENSITIVE stuck test */
 	__s64 last_delta2;		/* SENSITIVE stuck test */
+
+	unsigned int flags;		/* Flags used to initialize */
 	unsigned int osr;		/* Oversample rate */
 #define JENT_MEMORY_BLOCKS 64
 #define JENT_MEMORY_BLOCKSIZE 32
@@ -88,16 +90,9 @@ struct rand_data {
 	/* Repetition Count Test */
 	unsigned int rct_count;			/* Number of stuck values */
 
-	/* Intermittent health test failure threshold of 2^-30 */
-	/* From an SP800-90B perspective, this RCT cutoff value is equal to 31. */
-	/* However, our RCT implementation starts at 1, so we subtract 1 here. */
-#define JENT_RCT_CUTOFF		(31 - 1)	/* Taken from SP800-90B sec 4.4.1 */
-#define JENT_APT_CUTOFF		325			/* Taken from SP800-90B sec 4.4.2 */
-	/* Permanent health test failure threshold of 2^-60 */
-	/* From an SP800-90B perspective, this RCT cutoff value is equal to 61. */
-	/* However, our RCT implementation starts at 1, so we subtract 1 here. */
-#define JENT_RCT_CUTOFF_PERMANENT	(61 - 1)
-#define JENT_APT_CUTOFF_PERMANENT	355
+	/* Adaptive Proportion Test cutoff values */
+	unsigned int apt_cutoff; /* Intermittent health test failure */
+	unsigned int apt_cutoff_permanent; /* Permanent health test failure */
 #define JENT_APT_WINDOW_SIZE	512	/* Data window size */
 	/* LSB of time stamp to process */
 #define JENT_APT_LSB		16
@@ -122,6 +117,9 @@ struct rand_data {
 				   * zero). */
 #define JENT_ESTUCK		8 /* Too many stuck results during init. */
 #define JENT_EHEALTH		9 /* Health test failed during initialization */
+#define JENT_ERCT	       10 /* RCT failed during initialization */
+#define JENT_EHASH	       11 /* Hash self test failed */
+#define JENT_EMEM	       12 /* Can't allocate memory for initialization */
 
 /*
  * The output n bits can receive more than n bits of min entropy, of course,
@@ -147,6 +145,48 @@ struct rand_data {
  * This test complies with SP800-90B section 4.4.2.
  ***************************************************************************/
 
+/*
+ * See the SP 800-90B comment #10b for the corrected cutoff for the SP 800-90B
+ * APT.
+ * http://www.untruth.org/~josh/sp80090b/UL%20SP800-90B-final%20comments%20v1.9%2020191212.pdf
+ * In in the syntax of R, this is C = 2 + qbinom(1 − 2^(−30), 511, 2^(-1/osr)).
+ * (The original formula wasn't correct because the first symbol must
+ * necessarily have been observed, so there is no chance of observing 0 of these
+ * symbols.)
+ *
+ * For the alpha < 2^-53, R cannot be used as it uses a float data type without
+ * arbitrary precision. A SageMath script is used to calculate those cutoff
+ * values.
+ *
+ * For any value above 14, this yields the maximal allowable value of 512
+ * (by FIPS 140-2 IG 7.19 Resolution # 16, we cannot choose a cutoff value that
+ * renders the test unable to fail).
+ */
+static const unsigned int jent_apt_cutoff_lookup[15] = {
+	325, 422, 459, 477, 488, 494, 499, 502,
+	505, 507, 508, 509, 510, 511, 512 };
+static const unsigned int jent_apt_cutoff_permanent_lookup[15] = {
+	355, 447, 479, 494, 502, 507, 510, 512,
+	512, 512, 512, 512, 512, 512, 512 };
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+static void jent_apt_init(struct rand_data *ec, unsigned int osr)
+{
+	/*
+	 * Establish the apt_cutoff based on the presumed entropy rate of
+	 * 1/osr.
+	 */
+	if (osr >= ARRAY_SIZE(jent_apt_cutoff_lookup)) {
+		ec->apt_cutoff = jent_apt_cutoff_lookup[
+			ARRAY_SIZE(jent_apt_cutoff_lookup) - 1];
+		ec->apt_cutoff_permanent = jent_apt_cutoff_permanent_lookup[
+			ARRAY_SIZE(jent_apt_cutoff_permanent_lookup) - 1];
+	} else {
+		ec->apt_cutoff = jent_apt_cutoff_lookup[osr - 1];
+		ec->apt_cutoff_permanent =
+				jent_apt_cutoff_permanent_lookup[osr - 1];
+	}
+}
 /*
  * Reset the APT counter
  *
@@ -187,12 +227,12 @@ static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked)
 /* APT health test failure detection */
 static int jent_apt_permanent_failure(struct rand_data *ec)
 {
-	return (ec->apt_count >= JENT_APT_CUTOFF_PERMANENT) ? 1 : 0;
+	return (ec->apt_count >= ec->apt_cutoff_permanent) ? 1 : 0;
 }
 
 static int jent_apt_failure(struct rand_data *ec)
 {
-	return (ec->apt_count >= JENT_APT_CUTOFF) ? 1 : 0;
+	return (ec->apt_count >= ec->apt_cutoff) ? 1 : 0;
 }
 
 /***************************************************************************
@@ -275,15 +315,28 @@ static int jent_stuck(struct rand_data *ec, __u64 current_delta)
 	return 0;
 }
 
-/* RCT health test failure detection */
+/*
+ * The cutoff value is based on the following consideration:
+ * alpha = 2^-30 or 2^-60 as recommended in SP800-90B.
+ * In addition, we require an entropy value H of 1/osr as this is the minimum
+ * entropy required to provide full entropy.
+ * Note, we collect (DATA_SIZE_BITS + ENTROPY_SAFETY_FACTOR)*osr deltas for
+ * inserting them into the entropy pool which should then have (close to)
+ * DATA_SIZE_BITS bits of entropy in the conditioned output.
+ *
+ * Note, ec->rct_count (which equals to value B in the pseudo code of SP800-90B
+ * section 4.4.1) starts with zero. Hence we need to subtract one from the
+ * cutoff value as calculated following SP800-90B. Thus
+ * C = ceil(-log_2(alpha)/H) = 30*osr or 60*osr.
+ */
 static int jent_rct_permanent_failure(struct rand_data *ec)
 {
-	return (ec->rct_count >= JENT_RCT_CUTOFF_PERMANENT) ? 1 : 0;
+	return (ec->rct_count >= (60 * ec->osr)) ? 1 : 0;
 }
 
 static int jent_rct_failure(struct rand_data *ec)
 {
-	return (ec->rct_count >= JENT_RCT_CUTOFF) ? 1 : 0;
+	return (ec->rct_count >= (30 * ec->osr)) ? 1 : 0;
 }
 
 /* Report of health test failures */
@@ -448,7 +501,7 @@ static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
  *
  * @return result of stuck test
  */
-static int jent_measure_jitter(struct rand_data *ec)
+static int jent_measure_jitter(struct rand_data *ec, __u64 *ret_current_delta)
 {
 	__u64 time = 0;
 	__u64 current_delta = 0;
@@ -472,6 +525,10 @@ static int jent_measure_jitter(struct rand_data *ec)
 	if (jent_condition_data(ec, current_delta, stuck))
 		stuck = 1;
 
+	/* return the raw entropy value */
+	if (ret_current_delta)
+		*ret_current_delta = current_delta;
+
 	return stuck;
 }
 
@@ -489,11 +546,11 @@ static void jent_gen_entropy(struct rand_data *ec)
 		safety_factor = JENT_ENTROPY_SAFETY_FACTOR;
 
 	/* priming of the ->prev_time value */
-	jent_measure_jitter(ec);
+	jent_measure_jitter(ec, NULL);
 
 	while (!jent_health_failure(ec)) {
 		/* If a stuck measurement is received, repeat measurement */
-		if (jent_measure_jitter(ec))
+		if (jent_measure_jitter(ec, NULL))
 			continue;
 
 		/*
@@ -554,7 +611,8 @@ int jent_read_entropy(struct rand_data *ec, unsigned char *data,
 			 * Perform startup health tests and return permanent
 			 * error if it fails.
 			 */
-			if (jent_entropy_init(ec->hash_state))
+			if (jent_entropy_init(ec->osr, ec->flags,
+					      ec->hash_state))
 				return -3;
 
 			return -2;
@@ -604,11 +662,15 @@ struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
 
 	/* verify and set the oversampling rate */
 	if (osr == 0)
-		osr = 1; /* minimum sampling rate is 1 */
+		osr = 1; /* H_submitter = 1 / osr */
 	entropy_collector->osr = osr;
+	entropy_collector->flags = flags;
 
 	entropy_collector->hash_state = hash_state;
 
+	/* Initialize the APT */
+	jent_apt_init(entropy_collector, osr);
+
 	/* fill the data pad with non-zero values */
 	jent_gen_entropy(entropy_collector);
 
@@ -622,20 +684,14 @@ void jent_entropy_collector_free(struct rand_data *entropy_collector)
 	jent_zfree(entropy_collector);
 }
 
-int jent_entropy_init(void *hash_state)
+int jent_entropy_init(unsigned int osr, unsigned int flags, void *hash_state)
 {
-	int i;
-	__u64 delta_sum = 0;
-	__u64 old_delta = 0;
-	unsigned int nonstuck = 0;
-	int time_backwards = 0;
-	int count_mod = 0;
-	int count_stuck = 0;
-	struct rand_data ec = { 0 };
-
-	/* Required for RCT */
-	ec.osr = 1;
-	ec.hash_state = hash_state;
+	struct rand_data *ec;
+	int i, time_backwards = 0, ret = 0;
+
+	ec = jent_entropy_collector_alloc(osr, flags, hash_state);
+	if (!ec)
+		return JENT_EMEM;
 
 	/* We could perform statistical tests here, but the problem is
 	 * that we only have a few loop counts to do testing. These
@@ -664,31 +720,28 @@ int jent_entropy_init(void *hash_state)
 #define TESTLOOPCOUNT 1024
 #define CLEARCACHE 100
 	for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
-		__u64 time = 0;
-		__u64 time2 = 0;
-		__u64 delta = 0;
-		unsigned int lowdelta = 0;
-		int stuck;
+		__u64 start_time = 0, end_time = 0, delta = 0;
 
 		/* Invoke core entropy collection logic */
-		jent_get_nstime(&time);
-		ec.prev_time = time;
-		jent_condition_data(&ec, time, 0);
-		jent_get_nstime(&time2);
+		jent_measure_jitter(ec, &delta);
+		end_time = ec->prev_time;
+		start_time = ec->prev_time - delta;
 
 		/* test whether timer works */
-		if (!time || !time2)
-			return JENT_ENOTIME;
-		delta = jent_delta(time, time2);
+		if (!start_time || !end_time) {
+			ret = JENT_ENOTIME;
+			goto out;
+		}
+
 		/*
 		 * test whether timer is fine grained enough to provide
 		 * delta even when called shortly after each other -- this
 		 * implies that we also have a high resolution timer
 		 */
-		if (!delta)
-			return JENT_ECOARSETIME;
-
-		stuck = jent_stuck(&ec, delta);
+		if (!delta || (end_time == start_time)) {
+			ret = JENT_ECOARSETIME;
+			goto out;
+		}
 
 		/*
 		 * up to here we did not modify any variable that will be
@@ -700,49 +753,9 @@ int jent_entropy_init(void *hash_state)
 		if (i < CLEARCACHE)
 			continue;
 
-		if (stuck)
-			count_stuck++;
-		else {
-			nonstuck++;
-
-			/*
-			 * Ensure that the APT succeeded.
-			 *
-			 * With the check below that count_stuck must be less
-			 * than 10% of the overall generated raw entropy values
-			 * it is guaranteed that the APT is invoked at
-			 * floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times.
-			 */
-			if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) {
-				jent_apt_reset(&ec,
-					       delta & JENT_APT_WORD_MASK);
-			}
-		}
-
-		/* Validate health test result */
-		if (jent_health_failure(&ec))
-			return JENT_EHEALTH;
-
 		/* test whether we have an increasing timer */
-		if (!(time2 > time))
+		if (!(end_time > start_time))
 			time_backwards++;
-
-		/* use 32 bit value to ensure compilation on 32 bit arches */
-		lowdelta = time2 - time;
-		if (!(lowdelta % 100))
-			count_mod++;
-
-		/*
-		 * ensure that we have a varying delta timer which is necessary
-		 * for the calculation of entropy -- perform this check
-		 * only after the first loop is executed as we need to prime
-		 * the old_data value
-		 */
-		if (delta > old_delta)
-			delta_sum += (delta - old_delta);
-		else
-			delta_sum += (old_delta - delta);
-		old_delta = delta;
 	}
 
 	/*
@@ -752,31 +765,23 @@ int jent_entropy_init(void *hash_state)
 	 * should not fail. The value of 3 should cover the NTP case being
 	 * performed during our test run.
 	 */
-	if (time_backwards > 3)
-		return JENT_ENOMONOTONIC;
-
-	/*
-	 * Variations of deltas of time must on average be larger
-	 * than 1 to ensure the entropy estimation
-	 * implied with 1 is preserved
-	 */
-	if ((delta_sum) <= 1)
-		return JENT_EVARVAR;
+	if (time_backwards > 3) {
+		ret = JENT_ENOMONOTONIC;
+		goto out;
+	}
 
-	/*
-	 * Ensure that we have variations in the time stamp below 10 for at
-	 * least 10% of all checks -- on some platforms, the counter increments
-	 * in multiples of 100, but not always
-	 */
-	if ((TESTLOOPCOUNT/10 * 9) < count_mod)
-		return JENT_ECOARSETIME;
+	/* Did we encounter a health test failure? */
+	if (jent_rct_failure(ec)) {
+		ret = JENT_ERCT;
+		goto out;
+	}
+	if (jent_apt_failure(ec)) {
+		ret = JENT_EHEALTH;
+		goto out;
+	}
 
-	/*
-	 * If we have more than 90% stuck results, then this Jitter RNG is
-	 * likely to not work well.
-	 */
-	if ((TESTLOOPCOUNT/10 * 9) < count_stuck)
-		return JENT_ESTUCK;
+out:
+	jent_entropy_collector_free(ec);
 
-	return 0;
+	return ret;
 }
diff --git a/crypto/jitterentropy.h b/crypto/jitterentropy.h
index 4c92176ea2b1..626c6228b7e2 100644
--- a/crypto/jitterentropy.h
+++ b/crypto/jitterentropy.h
@@ -9,7 +9,8 @@ extern int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
 int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len);
 
 struct rand_data;
-extern int jent_entropy_init(void *hash_state);
+extern int jent_entropy_init(unsigned int osr, unsigned int flags,
+			     void *hash_state);
 extern int jent_read_entropy(struct rand_data *ec, unsigned char *data,
 			     unsigned int len);
 
-- 
2.42.0

[PATCH 2/3] crypto: jitter - Allow configuration of memory size

[Stephan Müller]

The memory size consumed by the Jitter RNG is one contributing factor in
the amount of entropy that is gathered. As the amount of entropy
directly correlates with the distance of the memory from the CPU, the
caches that are possibly present on a given system have an impact on the
collected entropy.

Thus, the kernel compile time should offer a means to configure the
amount of memory used by the Jitter RNG. Although this option could be
turned into a runtime option (e.g. a kernel command line option), it
should remain a compile time option as otherwise adminsitrators who may
not have performed an entropy assessment may select a value that is
inappropriate.

The default value selected by the configuration is identical to the
current Jitter RNG value. Thus, the patch should not lead to any change
in the Jitter RNG behavior.

To accommodate larger memory buffers, kvzalloc / kvfree is used.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 crypto/Kconfig               | 43 ++++++++++++++++++++++++++++++++++++
 crypto/jitterentropy-kcapi.c | 11 +++++++++
 crypto/jitterentropy.c       | 16 ++++++++------
 crypto/jitterentropy.h       |  2 ++
 4 files changed, 65 insertions(+), 7 deletions(-)

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 650b1b3620d8..00c827d9f0d2 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -1296,6 +1296,49 @@ config CRYPTO_JITTERENTROPY
 
 	  See https://www.chronox.de/jent.html
 
+choice
+	prompt "CPU Jitter RNG Memory Size"
+	default CRYPTO_JITTERENTROPY_MEMSIZE_2
+	depends on CRYPTO_JITTERENTROPY
+	help
+	  The Jitter RNG measures the execution time of memory accesses.
+	  Multiple consecutive memory accesses are performed. If the memory
+	  size fits into a cache (e.g. L1), only the memory access timing
+	  to that cache is measured. The closer the cache is to the CPU
+	  the less variations are measured and thus the less entropy is
+	  obtained. Thus, if the memory size fits into the L1 cache, the
+	  obtained entropy is less than if the memory size fits within
+	  L1 + L2, which in turn is less if the memory fits into
+	  L1 + L2 + L3. Thus, by selecting a different memory size,
+	  the entropy rate produced by the Jitter RNG can be modified.
+
+	config CRYPTO_JITTERENTROPY_MEMSIZE_2
+		bool "2048 Bytes (default)"
+
+	config CRYPTO_JITTERENTROPY_MEMSIZE_128
+		bool "128 kBytes"
+
+	config CRYPTO_JITTERENTROPY_MEMSIZE_1024
+		bool "1024 kBytes"
+
+	config CRYPTO_JITTERENTROPY_MEMSIZE_8192
+		bool "8192 kBytes"
+endchoice
+
+config CRYPTO_JITTERENTROPY_MEMORY_BLOCKS
+	int
+	default 64 if CRYPTO_JITTERENTROPY_MEMSIZE_2
+	default 512 if CRYPTO_JITTERENTROPY_MEMSIZE_128
+	default 1024 if CRYPTO_JITTERENTROPY_MEMSIZE_1024
+	default 4096 if CRYPTO_JITTERENTROPY_MEMSIZE_8192
+
+config CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE
+	int
+	default 32 if CRYPTO_JITTERENTROPY_MEMSIZE_2
+	default 256 if CRYPTO_JITTERENTROPY_MEMSIZE_128
+	default 1024 if CRYPTO_JITTERENTROPY_MEMSIZE_1024
+	default 2048 if CRYPTO_JITTERENTROPY_MEMSIZE_8192
+
 config CRYPTO_JITTERENTROPY_TESTINTERFACE
 	bool "CPU Jitter RNG Test Interface"
 	depends on CRYPTO_JITTERENTROPY
diff --git a/crypto/jitterentropy-kcapi.c b/crypto/jitterentropy-kcapi.c
index 1de730f94683..a8e7bbd28c6e 100644
--- a/crypto/jitterentropy-kcapi.c
+++ b/crypto/jitterentropy-kcapi.c
@@ -54,6 +54,17 @@
  * Helper function
  ***************************************************************************/
 
+void *jent_kvzalloc(unsigned int len)
+{
+	return kvzalloc(len, GFP_KERNEL);
+}
+
+void jent_kvzfree(void *ptr, unsigned int len)
+{
+	memzero_explicit(ptr, len);
+	kvfree(ptr);
+}
+
 void *jent_zalloc(unsigned int len)
 {
 	return kzalloc(len, GFP_KERNEL);
diff --git a/crypto/jitterentropy.c b/crypto/jitterentropy.c
index c99734af82b8..f224ceb1e2e3 100644
--- a/crypto/jitterentropy.c
+++ b/crypto/jitterentropy.c
@@ -75,10 +75,10 @@ struct rand_data {
 
 	unsigned int flags;		/* Flags used to initialize */
 	unsigned int osr;		/* Oversample rate */
-#define JENT_MEMORY_BLOCKS 64
-#define JENT_MEMORY_BLOCKSIZE 32
 #define JENT_MEMORY_ACCESSLOOPS 128
-#define JENT_MEMORY_SIZE (JENT_MEMORY_BLOCKS*JENT_MEMORY_BLOCKSIZE)
+#define JENT_MEMORY_SIZE						\
+	(CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKS *			\
+	 CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE)
 	unsigned char *mem;	/* Memory access location with size of
 				 * memblocks * memblocksize */
 	unsigned int memlocation; /* Pointer to byte in *mem */
@@ -650,13 +650,15 @@ struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
 		/* Allocate memory for adding variations based on memory
 		 * access
 		 */
-		entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE);
+		entropy_collector->mem = jent_kvzalloc(JENT_MEMORY_SIZE);
 		if (!entropy_collector->mem) {
 			jent_zfree(entropy_collector);
 			return NULL;
 		}
-		entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE;
-		entropy_collector->memblocks = JENT_MEMORY_BLOCKS;
+		entropy_collector->memblocksize =
+			CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE;
+		entropy_collector->memblocks =
+			CONFIG_CRYPTO_JITTERENTROPY_MEMORY_BLOCKS;
 		entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS;
 	}
 
@@ -679,7 +681,7 @@ struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
 
 void jent_entropy_collector_free(struct rand_data *entropy_collector)
 {
-	jent_zfree(entropy_collector->mem);
+	jent_kvzfree(entropy_collector->mem, JENT_MEMORY_SIZE);
 	entropy_collector->mem = NULL;
 	jent_zfree(entropy_collector);
 }
diff --git a/crypto/jitterentropy.h b/crypto/jitterentropy.h
index 626c6228b7e2..e31661ee00d3 100644
--- a/crypto/jitterentropy.h
+++ b/crypto/jitterentropy.h
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+extern void *jent_kvzalloc(unsigned int len);
+extern void jent_kvzfree(void *ptr, unsigned int len);
 extern void *jent_zalloc(unsigned int len);
 extern void jent_zfree(void *ptr);
 extern void jent_get_nstime(__u64 *out);
-- 
2.42.0

[PATCH 3/3] crypto: jitter - Allow configuration of oversampling rate

[Stephan Müller]

The oversampling rate used by the Jitter RNG allows the configuration of
the heuristically implied entropy in one timing measurement. This
entropy rate is (1 / OSR) bits of entropy per time stamp.

Considering that the Jitter RNG now support APT/RCT health tests for
different OSRs, allow this value to be configured at compile time to
support systems with limited amount of entropy in their timer.

The allowed range of OSR values complies with the APT/RCT cutoff health
test values which range from 1 through 15.

The default value of the OSR selection support is left at 1 which is the
current default. Thus, the addition of the configuration support does
not alter the default Jitter RNG behavior.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
---
 crypto/Kconfig               | 17 +++++++++++++++++
 crypto/jitterentropy-kcapi.c |  6 ++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 00c827d9f0d2..ed931ddea644 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -1339,6 +1339,23 @@ config CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE
 	default 1024 if CRYPTO_JITTERENTROPY_MEMSIZE_1024
 	default 2048 if CRYPTO_JITTERENTROPY_MEMSIZE_8192
 
+config CRYPTO_JITTERENTROPY_OSR
+	int "CPU Jitter RNG Oversampling Rate"
+	range 1 15
+	default 1
+	depends on CRYPTO_JITTERENTROPY
+	help
+	  The Jitter RNG allows the specification of an oversampling rate (OSR).
+	  The Jitter RNG operation requires a fixed amount of timing
+	  measurements to produce one output block of random numbers. The
+	  OSR value is multiplied with the amount of timing measurements to
+	  generate one output block. Thus, the timing measurement is oversampled
+	  by the OSR factor. The oversampling allows the Jitter RNG to operate
+	  on hardware whose timers deliver limited amount of entropy (e.g.
+	  the timer is coarse) by setting the OSR to a higher value. The
+	  trade-off, however, is that the Jitter RNG now requires more time
+	  to generate random numbers.
+
 config CRYPTO_JITTERENTROPY_TESTINTERFACE
 	bool "CPU Jitter RNG Test Interface"
 	depends on CRYPTO_JITTERENTROPY
diff --git a/crypto/jitterentropy-kcapi.c b/crypto/jitterentropy-kcapi.c
index a8e7bbd28c6e..0c6752221451 100644
--- a/crypto/jitterentropy-kcapi.c
+++ b/crypto/jitterentropy-kcapi.c
@@ -256,7 +256,9 @@ static int jent_kcapi_init(struct crypto_tfm *tfm)
 	crypto_shash_init(sdesc);
 	rng->sdesc = sdesc;
 
-	rng->entropy_collector = jent_entropy_collector_alloc(0, 0, sdesc);
+	rng->entropy_collector =
+		jent_entropy_collector_alloc(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0,
+					     sdesc);
 	if (!rng->entropy_collector) {
 		ret = -ENOMEM;
 		goto err;
@@ -345,7 +347,7 @@ static int __init jent_mod_init(void)
 
 	desc->tfm = tfm;
 	crypto_shash_init(desc);
-	ret = jent_entropy_init(0, 0, desc);
+	ret = jent_entropy_init(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, desc);
 	shash_desc_zero(desc);
 	crypto_free_shash(tfm);
 	if (ret) {
-- 
2.42.0

RE: [PATCH 0/3] crypto: jitter - Offer compile-time options

[Ospan, Abylay]

Hi Stephan,

We ran tests with your patches on our bare metal platform (AMD Epyc CPU) and saw an improvement in boot time entropy after analyzing the collected jitter deltas.
Patches looks good to me.
Thanks for your work!

Acked-by: Abylay Ospan <aospan@amazon.com>

-----Original Message-----
From: Stephan Müller <smueller@chronox.de> 
Sent: Thursday, September 21, 2023 7:48 AM
To: herbert@gondor.apana.org.au
Cc: linux-crypto@vger.kernel.org; Ospan, Abylay <aospan@amazon.com>
Subject: [EXTERNAL] [PATCH 0/3] crypto: jitter - Offer compile-time options

CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.



Hi,

the following patchset offers a set of compile-time options to accommodate different hardware with different entropy rates implied in their timers. This allows configuring the Jitter RNG in systems which exhibits insufficient entropy with the default parameters. The default parameters defined by the patches, however, are identical to the existing code and thus do not alter the Jitter RNG behavior.

The first patch sets the state by allowing the configuration of different oversampling rates. The second patch allows the configuration of different memory sizes and the third allows the configuration of differnet oversampling rates.

The update of the power up test with the first patch also addresses reports that the Jitter RNG did not initialize due to it detected insufficient entropy.

Stephan Mueller (3):
  crypto: jitter - add RCT/APT support for different OSRs
  crypto: jitter - Allow configuration of memory size
  crypto: jitter - Allow configuration of oversampling rate

 crypto/Kconfig               |  60 +++++++++
 crypto/jitterentropy-kcapi.c |  17 ++-
 crypto/jitterentropy.c       | 249 ++++++++++++++++++-----------------
 crypto/jitterentropy.h       |   5 +-
 4 files changed, 207 insertions(+), 124 deletions(-)

--
2.42.0

Re: [PATCH 0/3] crypto: jitter - Offer compile-time options

[Herbert Xu]

On Thu, Sep 21, 2023 at 01:47:32PM +0200, Stephan Müller wrote:
> Hi,
> 
> the following patchset offers a set of compile-time options to
> accommodate different hardware with different entropy rates implied
> in their timers. This allows configuring the Jitter RNG in systems
> which exhibits insufficient entropy with the default parameters. The
> default parameters defined by the patches, however, are identical to
> the existing code and thus do not alter the Jitter RNG behavior.
> 
> The first patch sets the state by allowing the configuration of
> different oversampling rates. The second patch allows the configuration
> of different memory sizes and the third allows the configuration
> of differnet oversampling rates.
> 
> The update of the power up test with the first patch also addresses
> reports that the Jitter RNG did not initialize due to it detected
> insufficient entropy.
> 
> Stephan Mueller (3):
>   crypto: jitter - add RCT/APT support for different OSRs
>   crypto: jitter - Allow configuration of memory size
>   crypto: jitter - Allow configuration of oversampling rate
> 
>  crypto/Kconfig               |  60 +++++++++
>  crypto/jitterentropy-kcapi.c |  17 ++-
>  crypto/jitterentropy.c       | 249 ++++++++++++++++++-----------------
>  crypto/jitterentropy.h       |   5 +-
>  4 files changed, 207 insertions(+), 124 deletions(-)
> 
> -- 
> 2.42.0

All applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt