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76 lines
3.0 KiB
Diff
76 lines
3.0 KiB
Diff
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From 0baa8fab334a4d7017235b72fa8a547433572109 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Stephan=20M=C3=BCller?= <smueller@chronox.de>
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Date: Thu, 21 Sep 2023 13:48:59 +0200
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Subject: [PATCH] crypto: jitter - Allow configuration of oversampling rate
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The oversampling rate used by the Jitter RNG allows the configuration of
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the heuristically implied entropy in one timing measurement. This
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entropy rate is (1 / OSR) bits of entropy per time stamp.
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Considering that the Jitter RNG now support APT/RCT health tests for
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different OSRs, allow this value to be configured at compile time to
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support systems with limited amount of entropy in their timer.
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The allowed range of OSR values complies with the APT/RCT cutoff health
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test values which range from 1 through 15.
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The default value of the OSR selection support is left at 1 which is the
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current default. Thus, the addition of the configuration support does
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not alter the default Jitter RNG behavior.
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Signed-off-by: Stephan Mueller <smueller@chronox.de>
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Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
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---
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crypto/Kconfig | 17 +++++++++++++++++
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crypto/jitterentropy-kcapi.c | 6 ++++--
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2 files changed, 21 insertions(+), 2 deletions(-)
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--- a/crypto/Kconfig
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+++ b/crypto/Kconfig
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@@ -1340,6 +1340,23 @@ config CRYPTO_JITTERENTROPY_MEMORY_BLOCK
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default 1024 if CRYPTO_JITTERENTROPY_MEMSIZE_1024
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default 2048 if CRYPTO_JITTERENTROPY_MEMSIZE_8192
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+config CRYPTO_JITTERENTROPY_OSR
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+ int "CPU Jitter RNG Oversampling Rate"
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+ range 1 15
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+ default 1
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+ depends on CRYPTO_JITTERENTROPY
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+ help
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+ The Jitter RNG allows the specification of an oversampling rate (OSR).
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+ The Jitter RNG operation requires a fixed amount of timing
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+ measurements to produce one output block of random numbers. The
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+ OSR value is multiplied with the amount of timing measurements to
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+ generate one output block. Thus, the timing measurement is oversampled
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+ by the OSR factor. The oversampling allows the Jitter RNG to operate
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+ on hardware whose timers deliver limited amount of entropy (e.g.
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+ the timer is coarse) by setting the OSR to a higher value. The
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+ trade-off, however, is that the Jitter RNG now requires more time
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+ to generate random numbers.
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+
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config CRYPTO_JITTERENTROPY_TESTINTERFACE
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bool "CPU Jitter RNG Test Interface"
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depends on CRYPTO_JITTERENTROPY
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--- a/crypto/jitterentropy-kcapi.c
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+++ b/crypto/jitterentropy-kcapi.c
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@@ -256,7 +256,9 @@ static int jent_kcapi_init(struct crypto
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crypto_shash_init(sdesc);
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rng->sdesc = sdesc;
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- rng->entropy_collector = jent_entropy_collector_alloc(0, 0, sdesc);
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+ rng->entropy_collector =
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+ jent_entropy_collector_alloc(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0,
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+ sdesc);
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if (!rng->entropy_collector) {
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ret = -ENOMEM;
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goto err;
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@@ -345,7 +347,7 @@ static int __init jent_mod_init(void)
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desc->tfm = tfm;
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crypto_shash_init(desc);
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- ret = jent_entropy_init(0, 0, desc);
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+ ret = jent_entropy_init(CONFIG_CRYPTO_JITTERENTROPY_OSR, 0, desc);
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shash_desc_zero(desc);
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crypto_free_shash(tfm);
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if (ret) {
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