Author: cem Date: Mon Dec 30 01:38:19 2019 New Revision: 356194 URL: https://svnweb.freebsd.org/changeset/base/356194
Log: random(4): Make entropy source deregistration safe Allow loadable modules that provide random entropy source(s) to safely unload. Prior to this change, no driver could ensure that their random_source structure was not being used by random_harvestq.c for any period of time after invoking random_source_deregister(). This change converts the source_list LIST to a ConcurrencyKit CK_LIST and uses an epoch(9) to protect typical read accesses of the list. The existing HARVEST_LOCK spin mutex is used to safely add and remove list entries. random_source_deregister() uses epoch_wait() to ensure no concurrent source_list readers are accessing a random_source before freeing the list item and returning to the caller. Callers can safely unload immediately after random_source_deregister() returns. Reviewed by: markj Approved by: csprng(markm) Discussed with: jhb Differential Revision: https://reviews.freebsd.org/D22489 Modified: head/sys/dev/random/random_harvestq.c Modified: head/sys/dev/random/random_harvestq.c ============================================================================== --- head/sys/dev/random/random_harvestq.c Mon Dec 30 00:49:49 2019 (r356193) +++ head/sys/dev/random/random_harvestq.c Mon Dec 30 01:38:19 2019 (r356194) @@ -34,7 +34,9 @@ __FBSDID("$FreeBSD$"); #include <sys/param.h> #include <sys/systm.h> +#include <sys/ck.h> #include <sys/conf.h> +#include <sys/epoch.h> #include <sys/eventhandler.h> #include <sys/hash.h> #include <sys/kernel.h> @@ -76,6 +78,14 @@ static void random_sources_feed(void); static u_int read_rate; /* + * Random must initialize much earlier than epoch, but we can initialize the + * epoch code before SMP starts. Prior to SMP, we can safely bypass + * concurrency primitives. + */ +static __read_mostly bool epoch_inited; +static __read_mostly epoch_t rs_epoch; + +/* * How many events to queue up. We create this many items in * an 'empty' queue, then transfer them to the 'harvest' queue with * supplied junk. When used, they are transferred back to the @@ -94,12 +104,12 @@ volatile int random_kthread_control; __read_frequently u_int hc_source_mask; struct random_sources { - LIST_ENTRY(random_sources) rrs_entries; + CK_LIST_ENTRY(random_sources) rrs_entries; struct random_source *rrs_source; }; -static LIST_HEAD(sources_head, random_sources) source_list = - LIST_HEAD_INITIALIZER(source_list); +static CK_LIST_HEAD(sources_head, random_sources) source_list = + CK_LIST_HEAD_INITIALIZER(source_list); SYSCTL_NODE(_kern_random, OID_AUTO, harvest, CTLFLAG_RW, 0, "Entropy Device Parameters"); @@ -202,6 +212,14 @@ random_kthread(void) SYSINIT(random_device_h_proc, SI_SUB_KICK_SCHEDULER, SI_ORDER_ANY, kproc_start, &random_proc_kp); +static void +rs_epoch_init(void *dummy __unused) +{ + rs_epoch = epoch_alloc("Random Sources", EPOCH_PREEMPT); + epoch_inited = true; +} +SYSINIT(rs_epoch_init, SI_SUB_EPOCH, SI_ORDER_ANY, rs_epoch_init, NULL); + /* * Run through all fast sources reading entropy for the given * number of rounds, which should be a multiple of the number @@ -211,9 +229,13 @@ static void random_sources_feed(void) { uint32_t entropy[HARVESTSIZE]; + struct epoch_tracker et; struct random_sources *rrs; u_int i, n, local_read_rate; + bool rse_warm; + rse_warm = epoch_inited; + /* * Step over all of live entropy sources, and feed their output * to the system-wide RNG. @@ -223,7 +245,9 @@ random_sources_feed(void) local_read_rate = MAX(local_read_rate, 1); /* But not exceeding RANDOM_KEYSIZE_WORDS */ local_read_rate = MIN(local_read_rate, RANDOM_KEYSIZE_WORDS); - LIST_FOREACH(rrs, &source_list, rrs_entries) { + if (rse_warm) + epoch_enter_preempt(rs_epoch, &et); + CK_LIST_FOREACH(rrs, &source_list, rrs_entries) { for (i = 0; i < p_random_alg_context->ra_poolcount*local_read_rate; i++) { n = rrs->rrs_source->rs_read(entropy, sizeof(entropy)); KASSERT((n <= sizeof(entropy)), ("%s: rs_read returned too much data (%u > %zu)", __func__, n, sizeof(entropy))); @@ -243,6 +267,8 @@ random_sources_feed(void) random_harvest_direct(entropy, n, rrs->rrs_source->rs_source); } } + if (rse_warm) + epoch_exit_preempt(rs_epoch, &et); explicit_bzero(entropy, sizeof(entropy)); } @@ -573,7 +599,10 @@ random_source_register(struct random_source *rsource) random_harvest_register_source(rsource->rs_source); printf("random: registering fast source %s\n", rsource->rs_ident); - LIST_INSERT_HEAD(&source_list, rrs, rrs_entries); + + RANDOM_HARVEST_LOCK(); + CK_LIST_INSERT_HEAD(&source_list, rrs, rrs_entries); + RANDOM_HARVEST_UNLOCK(); } void @@ -585,29 +614,40 @@ random_source_deregister(struct random_source *rsource random_harvest_deregister_source(rsource->rs_source); - LIST_FOREACH(rrs, &source_list, rrs_entries) + RANDOM_HARVEST_LOCK(); + CK_LIST_FOREACH(rrs, &source_list, rrs_entries) if (rrs->rrs_source == rsource) { - LIST_REMOVE(rrs, rrs_entries); + CK_LIST_REMOVE(rrs, rrs_entries); break; } - if (rrs != NULL) - free(rrs, M_ENTROPY); + RANDOM_HARVEST_UNLOCK(); + + if (rrs != NULL && epoch_inited) + epoch_wait_preempt(rs_epoch); + free(rrs, M_ENTROPY); } static int random_source_handler(SYSCTL_HANDLER_ARGS) { + struct epoch_tracker et; struct random_sources *rrs; struct sbuf sbuf; int error, count; + error = sysctl_wire_old_buffer(req, 0); + if (error != 0) + return (error); + sbuf_new_for_sysctl(&sbuf, NULL, 64, req); count = 0; - LIST_FOREACH(rrs, &source_list, rrs_entries) { + epoch_enter_preempt(rs_epoch, &et); + CK_LIST_FOREACH(rrs, &source_list, rrs_entries) { sbuf_cat(&sbuf, (count++ ? ",'" : "'")); sbuf_cat(&sbuf, rrs->rrs_source->rs_ident); sbuf_cat(&sbuf, "'"); } + epoch_exit_preempt(rs_epoch, &et); error = sbuf_finish(&sbuf); sbuf_delete(&sbuf); return (error); _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
