git.openwrt.org Git - openwrt/staging/xback.git/blob

   1 From 0baa8fab334a4d7017235b72fa8a547433572109 Mon Sep 17 00:00:00 2001
   2 From: =?UTF-8?q?Stephan=20M=C3=BCller?= <smueller@chronox.de>
   3 Date: Thu, 21 Sep 2023 13:48:59 +0200
   4 Subject: [PATCH] crypto: jitter - Allow configuration of oversampling rate
   5
   6 The oversampling rate used by the Jitter RNG allows the configuration of
   7 the heuristically implied entropy in one timing measurement. This
   8 entropy rate is (1 / OSR) bits of entropy per time stamp.
   9
  10 Considering that the Jitter RNG now support APT/RCT health tests for
  11 different OSRs, allow this value to be configured at compile time to
  12 support systems with limited amount of entropy in their timer.
  13
  14 The allowed range of OSR values complies with the APT/RCT cutoff health
  15 test values which range from 1 through 15.
  16
  17 The default value of the OSR selection support is left at 1 which is the
  18 current default. Thus, the addition of the configuration support does
  19 not alter the default Jitter RNG behavior.
  20
  21 Signed-off-by: Stephan Mueller <smueller@chronox.de>
  22 Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
  23 ---
  24  crypto/Kconfig               | 17 +++++++++++++++++
  25  crypto/jitterentropy-kcapi.c |  6 ++++--
  26  2 files changed, 21 insertions(+), 2 deletions(-)
  27
  28 --- a/crypto/Kconfig
  29 +++ b/crypto/Kconfig
  30 @@ -1340,6 +1340,23 @@ config CRYPTO_JITTERENTROPY_MEMORY_BLOCK
  31         default 1024 if CRYPTO_JITTERENTROPY_MEMSIZE_1024
  32         default 2048 if CRYPTO_JITTERENTROPY_MEMSIZE_8192
  33
  34 +config CRYPTO_JITTERENTROPY_OSR
  35 +       int "CPU Jitter RNG Oversampling Rate"
  36 +       range 1 15
  37 +       default 1
  38 +       depends on CRYPTO_JITTERENTROPY
  39 +       help
  40 +         The Jitter RNG allows the specification of an oversampling rate (OSR).
  41 +         The Jitter RNG operation requires a fixed amount of timing
  42 +         measurements to produce one output block of random numbers. The
  43 +         OSR value is multiplied with the amount of timing measurements to
  44 +         generate one output block. Thus, the timing measurement is oversampled
  45 +         by the OSR factor. The oversampling allows the Jitter RNG to operate
  46 +         on hardware whose timers deliver limited amount of entropy (e.g.
  47 +         the timer is coarse) by setting the OSR to a higher value. The
  48 +         trade-off, however, is that the Jitter RNG now requires more time
  49 +         to generate random numbers.
  50 +
  51  config CRYPTO_JITTERENTROPY_TESTINTERFACE
  52         bool "CPU Jitter RNG Test Interface"
  53         depends on CRYPTO_JITTERENTROPY
  54 --- a/crypto/jitterentropy-kcapi.c
  55 +++ b/crypto/jitterentropy-kcapi.c
  56 @@ -257,7 +257,9 @@ static int jent_kcapi_init(struct crypto
  57         crypto_shash_init(sdesc);
  58         rng->sdesc = sdesc;
  59
  60 -       rng->entropy_collector = jent_entropy_collector_alloc(0, 0, sdesc);
  61 +       rng->entropy_collector =
  62 +               jent_entropy_collector_alloc(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0,
  63 +                                            sdesc);
  64         if (!rng->entropy_collector) {
  65                 ret = -ENOMEM;
  66                 goto err;
  67 @@ -346,7 +348,7 @@ static int __init jent_mod_init(void)
  68
  69         desc->tfm = tfm;
  70         crypto_shash_init(desc);
  71 -       ret = jent_entropy_init(0, 0, desc);
  72 +       ret = jent_entropy_init(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, desc);
  73         shash_desc_zero(desc);
  74         crypto_free_shash(tfm);
  75         if (ret) {