upstream: Add protection for private keys at rest in RAM against

speculation and memory sidechannel attacks like Spectre, Meltdown, Rowhammer
and Rambleed. This change encrypts private keys when they are not in use with
a symmetic key that is derived from a relatively large "prekey" consisting of
random data (currently 16KB).

Attackers must recover the entire prekey with high accuracy before
they can attempt to decrypt the shielded private key, but the current
generation of attacks have bit error rates that, when applied
cumulatively to the entire prekey, make this unlikely.

Implementation-wise, keys are encrypted "shielded" when loaded and then
automatically and transparently unshielded when used for signatures or
when being saved/serialised.

Hopefully we can remove this in a few years time when computer
architecture has become less unsafe.

been in snaps for a bit already; thanks deraadt@

ok dtucker@ deraadt@

OpenBSD-Commit-ID: 19767213c312e46f94b303a512ef8e9218a39bd4

1 files changed, 8 insertions, 2 deletions

diff --git a/sshd.c b/sshd.c
index be23fbc80..735a11060 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshd.c,v 1.535 2019/06/06 05:13:13 otto Exp $ */
+/* $OpenBSD: sshd.c,v 1.536 2019/06/21 04:21:05 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1375,7 +1375,7 @@ set_process_rdomain(struct ssh *ssh, const char *name)
 
 static void
 accumulate_host_timing_secret(struct sshbuf *server_cfg,
-    const struct sshkey *key)
+    struct sshkey *key)
 {
         static struct ssh_digest_ctx *ctx;
         u_char *hash;
@@ -1723,6 +1723,12 @@ main(int ac, char **av)
                     &key, NULL)) != 0 && r != SSH_ERR_SYSTEM_ERROR)
                         do_log2(ll, "Unable to load host key \"%s\": %s",
                             options.host_key_files[i], ssh_err(r));
+                if (r == 0 && (r = sshkey_shield_private(key)) != 0) {
+                        do_log2(ll, "Unable to shield host key \"%s\": %s",
+                            options.host_key_files[i], ssh_err(r));
+                        sshkey_free(key);
+                        key = NULL;
+                }
                 if ((r = sshkey_load_public(options.host_key_files[i],
                     &pubkey, NULL)) != 0 && r != SSH_ERR_SYSTEM_ERROR)
                         do_log2(ll, "Unable to load host key \"%s\": %s",