[src/trunk]: src/sys/kern Make rndctl -E/-C reset entropy accounting.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/7dde3f9cd0d3
branches:  trunk
changeset: 971940:7dde3f9cd0d3
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sun May 10 02:56:12 2020 +0000

description:
Make rndctl -E/-C reset entropy accounting.

If we don't trust a source, it's unreasonable to trust any entropy it
previously provided, and we don't have any way to undo only the
effects of that source, so just zero our estimate of the entropy in
the pool and start over.

(However, keep the samples already in the pool -- just treat them as
though they had zero entropy and start gathering more.)

diffstat:

 sys/kern/kern_entropy.c |  70 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 68 insertions(+), 2 deletions(-)

diffs (109 lines):

diff -r 1d1d6573cb6e -r 7dde3f9cd0d3 sys/kern/kern_entropy.c
--- a/sys/kern/kern_entropy.c   Sun May 10 02:38:10 2020 +0000
+++ b/sys/kern/kern_entropy.c   Sun May 10 02:56:12 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_entropy.c,v 1.20 2020/05/10 01:29:40 riastradh Exp $      */
+/*     $NetBSD: kern_entropy.c,v 1.21 2020/05/10 02:56:12 riastradh Exp $      */
 
 /*-
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -75,7 +75,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.20 2020/05/10 01:29:40 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.21 2020/05/10 02:56:12 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -1932,6 +1932,40 @@
 }
 
 /*
+ * entropy_reset_xc(arg1, arg2)
+ *
+ *     Reset the current CPU's pending entropy to zero.
+ */
+static void
+entropy_reset_xc(void *arg1 __unused, void *arg2 __unused)
+{
+       uint32_t extra = entropy_timer();
+       struct entropy_cpu *ec;
+       int s;
+
+       /*
+        * Acquire the per-CPU state, blocking soft interrupts and
+        * causing hard interrupts to drop samples on the floor.
+        */
+       ec = percpu_getref(entropy_percpu);
+       s = splsoftserial();
+       KASSERT(!ec->ec_locked);
+       ec->ec_locked = true;
+       __insn_barrier();
+
+       /* Zero the pending count and enter a cycle count for fun.  */
+       ec->ec_pending = 0;
+       entpool_enter(ec->ec_pool, &extra, sizeof extra);
+
+       /* Release the per-CPU state.  */
+       KASSERT(ec->ec_locked);
+       __insn_barrier();
+       ec->ec_locked = false;
+       splx(s);
+       percpu_putref(entropy_percpu);
+}
+
+/*
  * entropy_ioctl(cmd, data)
  *
  *     Handle various /dev/random ioctl queries.
@@ -2165,7 +2199,9 @@
        case RNDCTL: {          /* Modify entropy source flags.  */
                rndctl_t *rndctl = data;
                const size_t n = sizeof(rs->name);
+               uint32_t resetflags = RND_FLAG_NO_ESTIMATE|RND_FLAG_NO_COLLECT;
                uint32_t flags;
+               bool reset = false, request = false;
 
                CTASSERT(sizeof(rs->name) == sizeof(rndctl->name));
 
@@ -2187,9 +2223,39 @@
                        }
                        flags = rs->flags & ~rndctl->mask;
                        flags |= rndctl->flags & rndctl->mask;
+                       if ((rs->flags & resetflags) == 0 &&
+                           (flags & resetflags) != 0)
+                               reset = true;
+                       if ((rs->flags ^ flags) & resetflags)
+                               request = true;
                        atomic_store_relaxed(&rs->flags, flags);
                }
                mutex_exit(&E->lock);
+
+               /*
+                * If we disabled estimation or collection, nix all the
+                * pending entropy and set needed to the maximum.
+                */
+               if (reset) {
+                       xc_broadcast(0, &entropy_reset_xc, NULL, NULL);
+                       mutex_enter(&E->lock);
+                       E->pending = 0;
+                       atomic_store_relaxed(&E->needed,
+                           ENTROPY_CAPACITY*NBBY);
+                       mutex_exit(&E->lock);
+               }
+
+               /*
+                * If we changed any of the estimation or collection
+                * flags, request new samples from everyone -- either
+                * to make up for what we just lost, or to get new
+                * samples from what we just added.
+                */
+               if (request) {
+                       mutex_enter(&E->lock);
+                       entropy_request(ENTROPY_CAPACITY);
+                       mutex_exit(&E->lock);
+               }
                break;
        }
        case RNDADDDATA: {      /* Enter seed into entropy pool.  */