crypto: jitter - set default OSR to 3

The user space Jitter RNG library uses the oversampling rate of 3 which
implies that each time stamp is credited with 1/3 bit of entropy. To
obtain 256 bits of entropy, 768 time stamps need to be sampled. The
increase in OSR is applied based on a report where the Jitter RNG is
used on a system exhibiting a challenging environment to collect
entropy.

This OSR default value is now applied to the Linux kernel version of
the Jitter RNG as well.

The increase in the OSR from 1 to 3 also implies that the Jitter RNG is
now slower by default.

Reported-by: Jeff Barnes <jeffbarnes@microsoft.com>
Signed-off-by: Stephan Mueller <smueller@chronox.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 72e2decb8c6aa3972544e63bd4f7cbfffee85cf6..a779cab668c24cebae5e75fbba0ff0a826f3b45b 100644 (file)
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -1305,7 +1305,7 @@ config CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE
 config CRYPTO_JITTERENTROPY_OSR
        int "CPU Jitter RNG Oversampling Rate"
        range 1 15
-       default 1
+       default 3
        help
          The Jitter RNG allows the specification of an oversampling rate (OSR).
          The Jitter RNG operation requires a fixed amount of timing