11.11.2019 23:26, Stephan Müller пишет: > Implement health tests for LRNG's slow noise sources as mandated by > SP-800-90B The file contains the following health tests: > > - stuck test: The stuck test calculates the first, second and third > discrete derivative of the time stamp to be processed by the LFSR. > Only if all three values are zero, the received time delta is > considered to be non-stuck. The other way round? > > - SP800-90B Repetition Count Test (RCT): The LRNG uses an enhanced > version of the RCT specified in SP800-90B section 4.4.1. Instead of > counting identical back-to-back values, the input to the RCT is the > counting of the stuck values during the processing of received > interrupt events. The RCT is applied with alpha=2^-30 compliant to > the recommendation of FIPS 140-2 IG 9.8. During the counting operation, > the LRNG always calculates the RCT cut-off value of C. If that value > exceeds the allowed cut-off value, the LRNG will trigger the health > test failure discussed below. An error is logged to the kernel log > that such RCT failure occurred. This test is only applied and > enforced in FIPS mode, i.e. when the kernel compiled with > CONFIG_CONFIG_FIPS is started with fips=1. > > - SP800-90B Adaptive Proportion Test (APT): The LRNG implements the > APT as defined in SP800-90B section 4.4.2. The assumed The sentence ends in the middle. > > The aforementioned health tests are applied to the first 1,024 time stamps > obtained from interrupt events. In case one error is identified for either > the RCT, or the APT, the collected entropy is invalidated and the > SP800-90B startup health test is restarted. > > As long as the SP800-90B startup health test is not completed, all LRNG > random number output interfaces that may block will block and not generate > any data. This implies that only those potentially blocking interfaces are > defined to provide random numbers that are seeded with the interrupt noise > source being SP800-90B compliant. All other output interfaces will not be > affected by the SP800-90B startup test and thus are not considered > SP800-90B compliant. > > At runtime, the SP800-90B APT and RCT are applied to each time stamp > generated for a received interrupt. When either the APT and RCT indicates > a noise source failure, the LRNG is reset to a state it has immediately > after boot: > > - all entropy counters are set to zero > > - the SP800-90B startup tests are re-performed which implies that > getrandom(2) would block again until new entropy was collected > > To summarize, the following rules apply: > > • SP800-90B compliant output interfaces > > - /dev/random > > - getrandom(2) system call > > - get_random_bytes kernel-internal interface when being triggered by > the callback registered with add_random_ready_callback > > • SP800-90B non-compliant output interfaces > > - /dev/urandom > > - get_random_bytes kernel-internal interface called directly > > - randomize_page kernel-internal interface > > - get_random_u32 and get_random_u64 kernel-internal interfaces > > - get_random_u32_wait, get_random_u64_wait, get_random_int_wait, and > get_random_long_wait kernel-internal interfaces > > If either the RCT, or the APT health test fails irrespective whether > during initialization or runtime, the following actions occur: > > 1. The entropy of the entire entropy pool is invalidated. > > 2. The primary and all secondary DRNGs are reset which imply that they > are treated as being not seeded and require a reseed during next > invocation. > > 3. The SP800-90B startup health test are initiated with all > implications of the startup tests. That implies that from that point > on, new events must be observed and its entropy must be inserted into > the entropy pool before random numbers are calculated from the > entropy pool. > > Further details on the SP800-90B compliance and the availability of all > test tools required to perform all tests mandated by SP800-90B are > provided at [1]. > > The entire health testing code is compile-time configurable. > > CC: "Eric W. Biederman" > CC: "Alexander E. Patrakov" > CC: "Ahmed S. Darwish" > CC: "Theodore Y. Ts'o" > CC: Willy Tarreau > CC: Matthew Garrett > CC: Vito Caputo > CC: Andreas Dilger > CC: Jan Kara > CC: Ray Strode > CC: William Jon McCann > CC: zhangjs > CC: Andy Lutomirski > CC: Florian Weimer > CC: Lennart Poettering > CC: Nicolai Stange > Reviewed-by: Roman Drahtmueller > Tested-by: Roman Drahtmüller > Tested-by: Marcelo Henrique Cerri > Tested-by: Neil Horman > Signed-off-by: Stephan Mueller > --- > drivers/char/lrng/Kconfig | 13 + > drivers/char/lrng/Makefile | 1 + > drivers/char/lrng/lrng_health.c | 424 ++++++++++++++++++++++++++++++++ > 3 files changed, 438 insertions(+) > create mode 100644 drivers/char/lrng/lrng_health.c > > diff --git a/drivers/char/lrng/Kconfig b/drivers/char/lrng/Kconfig > index efc5f9aaa2a3..4373a1a19538 100644 > --- a/drivers/char/lrng/Kconfig > +++ b/drivers/char/lrng/Kconfig > @@ -113,4 +113,17 @@ config LRNG_TRNG_SUPPORT > With the TRNG support the /dev/random device will block > if insufficient entropy is available. > > +config LRNG_HEALTH_TESTS > + bool "Enable noise source online health tests" > + help > + The online health tests validate the noise source at > + runtime for fatal errors. These tests include SP800-90B > + compliant tests which are invoked if the system is booted > + with fips=1. In case of fatal errors during active > + SP800-90B tests, the issue is logged and the noise > + data is discarded. These tests are required for full > + compliance with SP800-90B. How have you tested that these tests work at runtime? Maybe add some code under a new CONFIG item that depends on CONFIG_BROKEN that deliberately botches the RNG and triggers failures? > + > + If unsure, say Y. > + > endif # LRNG > diff --git a/drivers/char/lrng/Makefile b/drivers/char/lrng/Makefile > index 1c72bc060bce..0713e9c0aa6e 100644 > --- a/drivers/char/lrng/Makefile > +++ b/drivers/char/lrng/Makefile > @@ -15,3 +15,4 @@ obj-$(CONFIG_LRNG_DRBG) += lrng_drbg.o > obj-$(CONFIG_LRNG_KCAPI) += lrng_kcapi.o > obj-$(CONFIG_LRNG_JENT) += lrng_jent.o > obj-$(CONFIG_LRNG_TRNG_SUPPORT) += lrng_trng.o > +obj-$(CONFIG_LRNG_HEALTH_TESTS) += lrng_health.o > diff --git a/drivers/char/lrng/lrng_health.c b/drivers/char/lrng/lrng_health.c > new file mode 100644 > index 000000000000..b8d96cec1f71 > --- /dev/null > +++ b/drivers/char/lrng/lrng_health.c > @@ -0,0 +1,424 @@ > +// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause > +/* > + * Linux Random Number Generator (LRNG) Health Testing > + * > + * Copyright (C) 2019, Stephan Mueller > + * > + * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED > + * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES > + * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF > + * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE > + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR > + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT > + * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR > + * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF > + * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT > + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE > + * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH > + * DAMAGE. > + */ > + > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > + > +#include > +#include > + > +#include "lrng_internal.h" > + > +/* Stuck Test */ > +struct lrng_stuck_test { > + u32 last_time; /* Stuck test: time of previous IRQ */ > + u32 last_delta; /* Stuck test: delta of previous IRQ */ > + u32 last_delta2; /* Stuck test: 2. time derivation of prev IRQ */ > +}; > + > +/* Repetition Count Test */ > +struct lrng_rct { > + atomic_t rct_count; /* Number of stuck values */ > +}; > + > +/* Adaptive Proportion Test */ > +struct lrng_apt { > + /* Taken from SP800-90B sec 4.4.2 - significance level 2^-30 */ > +#define LRNG_APT_CUTOFF 325 > + /* Data window size */ > +#define LRNG_APT_WINDOW_SIZE 512 > + /* LSB of time stamp to process */ > +#define LRNG_APT_LSB 16 > +#define LRNG_APT_WORD_MASK (LRNG_APT_LSB - 1) > + atomic_t apt_count; /* APT counter */ > + atomic_t apt_base; /* APT base reference */ > + > + atomic_t apt_trigger; > + bool apt_base_set; /* Is APT base set? */ > +}; > + > +/* The health test code must operate lock-less */ > +struct lrng_health { > + struct lrng_rct rct; > + struct lrng_apt apt; > + > + bool health_test_enabled; > + > + /* SP800-90B startup health tests */ > +#define LRNG_SP80090B_STARTUP_SAMPLES 1024 > +#define LRNG_SP80090B_STARTUP_BLOCKS ((LRNG_SP80090B_STARTUP_SAMPLES + \ > + LRNG_APT_WINDOW_SIZE - 1) / \ > + LRNG_APT_WINDOW_SIZE) > + bool sp80090b_startup_done; > + atomic_t sp80090b_startup_blocks; > +}; > + > +static struct lrng_health lrng_health = { > + .rct.rct_count = ATOMIC_INIT(0), > + > + .apt.apt_count = ATOMIC_INIT(0), > + .apt.apt_base = ATOMIC_INIT(-1), > + .apt.apt_trigger = ATOMIC_INIT(LRNG_APT_WINDOW_SIZE), > + .apt.apt_base_set = false, > + > + .health_test_enabled = true, > + > + .sp80090b_startup_blocks = ATOMIC_INIT(LRNG_SP80090B_STARTUP_BLOCKS), > + .sp80090b_startup_done = false, > +}; > + > +static DEFINE_PER_CPU(struct lrng_stuck_test, lrng_stuck_test); > + > +static inline bool lrng_sp80090b_health_requested(void) > +{ > + /* Health tests are only requested in FIPS mode */ > + return fips_enabled; > +} > + > +static inline bool lrng_sp80090b_health_enabled(void) > +{ > + struct lrng_health *health = &lrng_health; > + > + return lrng_sp80090b_health_requested() && health->health_test_enabled; > +} > + > +/*************************************************************************** > + * SP800-90B Compliance > + * > + * If the Linux-RNG is booted into FIPS mode, the following interfaces > + * provide an SP800-90B compliant noise source: > + * > + * * /dev/random > + * * getrandom(2) > + * * get_random_bytes when using it in conjunction with > + * add_random_ready_callback > + * > + * All other interfaces, including /dev/urandom or get_random_bytes without > + * the add_random_ready_callback cannot claim to use an SP800-90B compliant > + * noise source. > + ***************************************************************************/ > + > +/** > + * Perform SP800-90B startup testing > + */ > +static inline void lrng_sp80090b_startup(struct lrng_health *health) > +{ > + if (!health->sp80090b_startup_done && > + atomic_dec_and_test(&health->sp80090b_startup_blocks)) { > + health->sp80090b_startup_done = true; > + pr_info("SP800-90B startup health tests completed\n"); > + lrng_init_ops(0); > + > + /* > + * Force a reseed of secondary DRNGs to ensure they are > + * seeded with entropy that passed the SP800-90B health tests. > + * As the primary DRNG always will reseed before generating > + * random numbers, it does not need a reseed trigger. > + */ > + lrng_sdrng_force_reseed(); > + } > +} > + > +/** > + * Handle failure of SP800-90B startup testing > + */ > +static inline void lrng_sp80090b_startup_failure(struct lrng_health *health) > +{ > + /* Reset of LRNG and its entropy - NOTE: we are in atomic context */ > + lrng_reset(); > + > + /* > + * Reset the SP800-90B startup test. > + * > + * NOTE SP800-90B section 4.3 bullet 4 does not specify what > + * exactly is to be done in case of failure! Thus, we do what > + * makes sense, i.e. restarting the health test and thus gating > + * the output function of /dev/random and getrandom(2). > + */ > + atomic_set(&health->sp80090b_startup_blocks, > + LRNG_SP80090B_STARTUP_BLOCKS); > +} > + > +/** > + * Handle failure of SP800-90B runtime testing > + */ > +static inline void lrng_sp80090b_runtime_failure(struct lrng_health *health) > +{ > + lrng_sp80090b_startup_failure(health); > + health->sp80090b_startup_done = false; > +} > + > +static inline void lrng_sp80090b_failure(struct lrng_health *health) > +{ > + if (health->sp80090b_startup_done) { > + pr_err("SP800-90B runtime health test failure - invalidating " > + "all existing entropy and initiate SP800-90B startup\n"); > + lrng_sp80090b_runtime_failure(health); > + } else { > + pr_err("SP800-90B startup test failure - resetting\n"); > + lrng_sp80090b_startup_failure(health); > + } > +} > + > +/** > + * Is the SP800-90B startup testing complete? > + * > + * This function is called by the LRNG to determine whether to unblock > + * a certain user interface. Therefore, only the potentially blocking > + * user interfaces are considered SP800-90B compliant. > + */ > +bool lrng_sp80090b_startup_complete(void) > +{ > + struct lrng_health *health = &lrng_health; > + > + return (lrng_sp80090b_health_enabled()) ? health->sp80090b_startup_done: > + true; > +} > + > +bool lrng_sp80090b_compliant(void) > +{ > + struct lrng_health *health = &lrng_health; > + > + return lrng_sp80090b_health_enabled() && health->sp80090b_startup_done; > +} > + > +/*************************************************************************** > + * Adaptive Proportion Test > + * > + * This test complies with SP800-90B section 4.4.2. > + ***************************************************************************/ > + > +/** > + * Reset the APT counter > + * > + * @health [in] Reference to health state > + */ > +static inline void lrng_apt_reset(struct lrng_health *health, > + unsigned int time_masked) > +{ > + struct lrng_apt *apt = &health->apt; > + > + pr_debug("APT value %d for base %d\n", > + atomic_read(&apt->apt_count), atomic_read(&apt->apt_base)); > + > + /* Reset APT */ > + atomic_set(&apt->apt_count, 0); > + atomic_set(&apt->apt_base, time_masked); > +} > + > +static inline void lrng_apt_restart(struct lrng_health *health) > +{ > + struct lrng_apt *apt = &health->apt; > + > + atomic_set(&apt->apt_trigger, LRNG_APT_WINDOW_SIZE); > +} > + > +/** > + * Insert a new entropy event into APT > + * > + * This function does is void as it does not decide about the fate of a time > + * stamp. An APT failure can only happen at the same time of a stuck test > + * failure. Thus, the stuck failure will already decide how the time stamp > + * is handled. > + * > + * @health [in] Reference to health state > + * @now_time [in] Time stamp to process > + */ > +static inline void lrng_apt_insert(struct lrng_health *health, > + unsigned int now_time) > +{ > + struct lrng_apt *apt = &health->apt; > + > + if (!lrng_sp80090b_health_requested()) > + return; > + > + now_time &= LRNG_APT_WORD_MASK; > + > + /* Initialization of APT */ > + if (!apt->apt_base_set) { > + atomic_set(&apt->apt_base, now_time); > + apt->apt_base_set = true; > + return; > + } > + > + if (now_time == (unsigned int)atomic_read(&apt->apt_base)) { > + u32 apt_val = (u32)atomic_inc_return_relaxed(&apt->apt_count); > + > + if (apt_val >= LRNG_APT_CUTOFF) > + lrng_sp80090b_failure(health); > + } > + > + if (atomic_dec_and_test(&apt->apt_trigger)) { > + lrng_apt_restart(health); > + lrng_apt_reset(health, now_time); > + lrng_sp80090b_startup(health); > + } > +} > + > +/*************************************************************************** > + * Repetition Count Test > + * > + * The LRNG uses an enhanced version of the Repetition Count Test > + * (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical > + * back-to-back values, the input to the RCT is the counting of the stuck > + * values while filling the entropy pool. > + * > + * The RCT is applied with an alpha of 2^-30 compliant to FIPS 140-2 IG 9.8. > + * > + * During the counting operation, the LRNG always calculates the RCT > + * cut-off value of C. If that value exceeds the allowed cut-off value, > + * the LRNG will invalidate all entropy for the entropy pool which implies > + * that no data can be extracted from the entropy pool unless new entropy > + * is received. > + ***************************************************************************/ > + > +/** > + * Hot code path - Insert data for Repetition Count Test > + * > + * @health: Reference to health information > + * @stuck: Decision of stuck test > + */ > +static inline void lrng_rct(struct lrng_health *health, int stuck) > +{ > + struct lrng_rct *rct = &health->rct; > + > + if (!lrng_sp80090b_health_requested()) > + return; > + > + if (stuck) { > + u32 rct_count = atomic_add_return_relaxed(1, &rct->rct_count); > + > + pr_debug("RCT count: %u\n", rct_count); > + > + /* > + * The cutoff value is based on the following consideration: > + * alpha = 2^-30 as recommended in FIPS 140-2 IG 9.8. > + * In addition, we imply an entropy value H of 1 bit as this > + * is the minimum entropy required to provide full entropy. > + * > + * Note, 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. > + */ > + if (rct_count >= 30) { > + atomic_set(&rct->rct_count, 0); > + > + /* > + * APT must start anew as we consider all previously > + * recorded data to contain no entropy. > + */ > + lrng_apt_restart(health); > + > + lrng_sp80090b_failure(health); > + } > + } else { > + atomic_set(&rct->rct_count, 0); > + } > +} > + > +/*************************************************************************** > + * Stuck Test > + * > + * Checking the: > + * 1st derivative of the event occurrence (time delta) > + * 2nd derivative of the event occurrence (delta of time deltas) > + * 3rd derivative of the event occurrence (delta of delta of time deltas) > + * > + * All values must always be non-zero. The stuck test is only valid disabled if > + * high-resolution time stamps are identified after initialization. > + ***************************************************************************/ > + > +static inline u32 lrng_delta(u32 prev, u32 next) > +{ > + /* > + * Note that this (unsigned) subtraction does yield the correct value > + * in the wraparound-case, i.e. when next < prev. > + */ > + return (next - prev); > +} > + > +/** > + * Hot code path > + * > + * @health: Reference to health information > + * @now: Event time > + * @return: 0 event occurrence not stuck (good time stamp) > + * != 0 event occurrence stuck (reject time stamp) > + */ > +static inline int lrng_irq_stuck(struct lrng_stuck_test *stuck, u32 now_time) > +{ > + u32 delta = lrng_delta(stuck->last_time, now_time); > + u32 delta2 = lrng_delta(stuck->last_delta, delta); > + u32 delta3 = lrng_delta(stuck->last_delta2, delta2); > + > + stuck->last_time = now_time; > + stuck->last_delta = delta; > + stuck->last_delta2 = delta2; > + > + if (!delta || !delta2 || !delta3) > + return 1; > + > + return 0; > +} > + > +/*************************************************************************** > + * Health test interfaces > + ***************************************************************************/ > + > +/** > + * Disable all health tests > + */ > +void lrng_health_disable(void) > +{ > + struct lrng_health *health = &lrng_health; > + > + health->health_test_enabled = false; > + > + if (lrng_sp80090b_health_requested()) > + pr_warn("SP800-90B compliance requested but the Linux RNG is " > + "NOT SP800-90B compliant\n"); > +} > + > +/** > + * Hot code path - Perform health test on time stamp received from an event > + * > + * @now_time Time stap > + */ > +enum lrng_health_res lrng_health_test(u32 now_time) > +{ > + struct lrng_health *health = &lrng_health; > + struct lrng_stuck_test *stuck_test = this_cpu_ptr(&lrng_stuck_test); > + int stuck; > + > + if (!health->health_test_enabled) > + return lrng_health_pass; > + > + lrng_apt_insert(health, now_time); > + > + stuck = lrng_irq_stuck(stuck_test, now_time); > + lrng_rct(health, stuck); > + if (stuck) { > + /* SP800-90B disallows using a failing health test time stamp */ > + return lrng_sp80090b_health_requested() ? > + lrng_health_fail_drop : lrng_health_fail_use; > + } > + > + return lrng_health_pass; > +} > -- Alexander E. Patrakov