crypto: jitter - add interface for gathering of raw entropy

The test interface allows a privileged process to capture the raw
unconditioned noise that is collected by the Jitter RNG for statistical
analysis. Such testing allows the analysis how much entropy
the Jitter RNG noise source provides on a given platform. The obtained
data is the time stamp sampled by the Jitter RNG. Considering that
the Jitter RNG inserts the delta of this time stamp compared to the
immediately preceding time stamp, the obtained data needs to be
post-processed accordingly to obtain the data the Jitter RNG inserts
into its entropy pool.

The raw entropy collection is provided to obtain the raw unmodified
time stamps that are about to be added to the Jitter RNG entropy pool
and are credited with entropy. Thus, this patch adds an interface
which renders the Jitter RNG insecure. This patch is NOT INTENDED
FOR PRODUCTION SYSTEMS, but solely for development/test systems to
verify the available entropy rate.

Access to the data is given through the jent_raw_hires debugfs file.
The data buffer should be multiples of sizeof(u32) to fill the entire
buffer. Using the option jitterentropy_testing.boot_raw_hires_test=1
the raw noise of the first 1000 entropy events since boot can be
sampled.

This test interface allows generating the data required for
analysis whether the Jitter RNG is in compliance with SP800-90B
sections 3.1.3 and 3.1.4.

If the test interface is not compiled, its code is a noop which has no
impact on the performance.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 20 insertions, 0 deletions

diff --git a/crypto/Kconfig b/crypto/Kconfig
index d20f559e8a27..42751d63cd4d 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -1288,6 +1288,26 @@ config CRYPTO_JITTERENTROPY
 
 	  See https://www.chronox.de/jent.html
 
+config CRYPTO_JITTERENTROPY_TESTINTERFACE
+	bool "CPU Jitter RNG Test Interface"
+	depends on CRYPTO_JITTERENTROPY
+	help
+	  The test interface allows a privileged process to capture
+	  the raw unconditioned high resolution time stamp noise that
+	  is collected by the Jitter RNG for statistical analysis. As
+	  this data is used at the same time to generate random bits,
+	  the Jitter RNG operates in an insecure mode as long as the
+	  recording is enabled. This interface therefore is only
+	  intended for testing purposes and is not suitable for
+	  production systems.
+
+	  The raw noise data can be obtained using the jent_raw_hires
+	  debugfs file. Using the option
+	  jitterentropy_testing.boot_raw_hires_test=1 the raw noise of
+	  the first 1000 entropy events since boot can be sampled.
+
+	  If unsure, select N.
+
 config CRYPTO_KDF800108_CTR
 	tristate
 	select CRYPTO_HMAC