Make SSL handshakes much faster

This change boosts SSL handshake performance from 2,627 to ~10,000 per
second which is the same level of performance as NGINX at establishing
secure connections. That's impressive if we consider that redbean is a
forking frontend application server. This was accomplished by:

  1. Enabling either SSL session caching or SSL tickets. We choose to
     use tickets since they reduce network round trips too and that's
     a more important metric than wrk'ing localhost.

  2. Fixing mbedtls_mpi_sub_abs() which is the most frequently called
     function. It's called about 12,000 times during an SSL handshake
     since it's the basis of most arithmetic operations like addition
     and for some strange reason it was designed to make two needless
     copies in addition to calling malloc and free. That's now fixed.

  3. Improving TLS output buffering during the SSL handshake only, so
     that only a single is write and read system call is needed until
     blocking on the ping pong.

redbean will now do a better job wiping sensitive memory from a child
process as soon as it's not needed. The nice thing about fork is it's
much faster than reverse proxying so the goal is to use the different
address spaces along with setuid() to minimize the risk that a server
key will be compromised in the event that application code is hacked.

net/https/getsslroots.c

@@ -20,6 +20,8 @@
 #include "libc/calls/struct/dirent.h"
 #include "libc/errno.h"
 #include "libc/log/check.h"
+#include "libc/log/log.h"
+#include "libc/mem/mem.h"
 #include "libc/runtime/runtime.h"
 #include "libc/str/str.h"
 #include "libc/sysv/consts/dt.h"

net/https/https.mk

@@ -20,6 +20,8 @@ NET_HTTPS_A_CHECKS =				\
 	$(NET_HTTPS_A_HDRS:%=o/$(MODE)/%.ok)
 
 NET_HTTPS_A_DIRECTDEPS =			\
+	LIBC_BITS				\
+	LIBC_CALLS				\
 	LIBC_FMT				\
 	LIBC_INTRIN				\
 	LIBC_LOG				\

net/https/sslcache.c

@@ -0,0 +1,172 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2021 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/bits/bits.h"
+#include "libc/bits/safemacros.internal.h"
+#include "libc/calls/calls.h"
+#include "libc/log/check.h"
+#include "libc/log/log.h"
+#include "libc/macros.internal.h"
+#include "libc/nexgen32e/rdtsc.h"
+#include "libc/runtime/runtime.h"
+#include "libc/sysv/consts/map.h"
+#include "libc/sysv/consts/prot.h"
+#include "net/https/sslcache.h"
+#include "third_party/mbedtls/ssl.h"
+#include "third_party/mbedtls/x509_crt.h"
+
+static uint32_t HashSslSession(mbedtls_ssl_session *session) {
+  int i;
+  uint32_t h;
+  h = session->ciphersuite;
+  h *= 0x9e3779b1;
+  h = session->compression;
+  h *= 0x9e3779b1;
+  for (i = 0; i < session->id_len; i++) {
+    h += session->id[i];
+    h *= 0x9e3779b1;
+  }
+  return h;
+}
+
+struct SslCache *CreateSslCache(size_t bytes, int lifetime) {
+  struct SslCache *c;
+  size_t ents, size;
+  ents = rounddown2pow(MAX(2, bytes / sizeof(struct SslCacheEntry)));
+  size = sizeof(struct SslCache) + sizeof(struct SslCacheEntry) * ents;
+  size = ROUNDUP(size, FRAMESIZE);
+  CHECK_NE(MAP_FAILED, (c = mmap(NULL, size, PROT_READ | PROT_WRITE,
+                                 MAP_SHARED | MAP_ANONYMOUS, -1, 0)));
+  VERBOSEF("ssl cache %,zu bytes with %,u slots", size, ents);
+  c->lifetime = lifetime > 0 ? lifetime : 24 * 60 * 60;
+  c->size = size;
+  c->mask = ents - 1;
+  return c;
+}
+
+void FreeSslCache(struct SslCache *cache) {
+  if (!cache) return;
+  CHECK_NE(-1, munmap(cache, cache->size));
+}
+
+int UncacheSslSession(void *data, mbedtls_ssl_session *session) {
+  int64_t ts;
+  uint64_t tick;
+  unsigned char *ticket;
+  struct SslCache *cache;
+  mbedtls_x509_crt *cert;
+  struct SslCacheEntry *e;
+  uint32_t i, hash, ticketlen;
+  cache = data;
+  hash = HashSslSession(session);
+  i = hash & cache->mask;
+  e = cache->p + i;
+  if (!(tick = e->tick) || hash != e->hash) {
+    NOISEF("%u empty", i);
+    return 1;
+  }
+  asm volatile("" ::: "memory");
+  if (session->ciphersuite != e->session.ciphersuite ||
+      session->compression != e->session.compression ||
+      session->id_len != e->session.id_len ||
+      memcmp(session->id, e->session.id, e->session.id_len)) {
+    VERBOSEF("%u ssl cache collision", i);
+    return 1;
+  }
+  ts = time(0);
+  if (!(e->time <= ts && ts <= e->time + cache->lifetime)) {
+    DEBUGF("%u ssl cache expired", i);
+    lockcmpxchg(&e->tick, tick, 0);
+    return 1;
+  }
+  cert = 0;
+  ticket = 0;
+  if ((e->certlen && (!(cert = calloc(1, sizeof(*cert))) ||
+                      mbedtls_x509_crt_parse_der(cert, e->cert, e->certlen)))) {
+    goto Contention;
+  }
+  if ((ticketlen = e->ticketlen)) {
+    if (!(ticket = malloc(ticketlen))) goto Contention;
+    memcpy(ticket, e->ticket, ticketlen);
+  }
+  mbedtls_ssl_session_free(session);
+  memcpy(session, &e->session, sizeof(*session));
+  asm volatile("" ::: "memory");
+  if (tick != e->tick) goto Contention;
+  session->peer_cert = cert;
+  session->ticket = ticket;
+  session->ticket_len = ticketlen;
+  DEBUGF("%u restored ssl from cache", i);
+  return 0;
+Contention:
+  WARNF("%u ssl cache contention 0x%08x", i, hash);
+  mbedtls_x509_crt_free(cert);
+  free(ticket);
+  free(cert);
+  return 1;
+}
+
+int CacheSslSession(void *data, const mbedtls_ssl_session *session) {
+  int pid;
+  uint64_t tick;
+  uint32_t i, hash;
+  struct SslCache *cache;
+  struct SslCacheEntry *e;
+  cache = data;
+  if (session->peer_cert &&
+      session->peer_cert->raw.len > sizeof(cache->p[0].cert)) {
+    WARNF("%s too big %zu", "cert", session->peer_cert->raw.len);
+    return 1;
+  }
+  if (session->ticket && session->ticket_len > sizeof(cache->p[0].ticket)) {
+    WARNF("%s too big %zu", "ticket", session->ticket_len);
+    return 1;
+  }
+  pid = getpid();
+  hash = HashSslSession(session);
+  i = hash & cache->mask;
+  e = cache->p + i;
+  e->tick = 0;
+  e->pid = pid;
+  asm volatile("" ::: "memory");
+  memcpy(&e->session, session, sizeof(*session));
+  if (session->peer_cert) {
+    e->certlen = session->peer_cert->raw.len;
+    memcpy(e->cert, session->peer_cert->raw.p, session->peer_cert->raw.len);
+  } else {
+    e->certlen = 0;
+  }
+  if (session->ticket) {
+    e->ticketlen = session->ticket_len;
+    memcpy(e->ticket, session->ticket, session->ticket_len);
+  } else {
+    e->ticketlen = 0;
+  }
+  e->hash = hash;
+  e->time = time(0);
+  tick = unsignedsubtract(rdtsc(), kStartTsc);
+  asm volatile("" ::: "memory");
+  if (lockcmpxchg(&e->pid, pid, 0)) {
+    DEBUGF("%u saved", i);
+    e->tick = tick;
+    return 0;
+  } else {
+    WARNF("%u congestion", i);
+    return 1;
+  }
+}

net/https/sslcache.h

@@ -0,0 +1,31 @@
+#ifndef COSMOPOLITAN_NET_HTTPS_SSLCACHE_H_
+#define COSMOPOLITAN_NET_HTTPS_SSLCACHE_H_
+#include "third_party/mbedtls/ssl.h"
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+struct SslCache {
+  size_t size;
+  int lifetime;
+  uint32_t mask;
+  struct SslCacheEntry {
+    int64_t time;
+    volatile uint64_t tick;
+    volatile int pid;
+    uint32_t hash;
+    unsigned certlen;
+    unsigned ticketlen;
+    mbedtls_ssl_session session;
+    uint8_t cert[1500];
+    uint8_t ticket[500];
+  } p[];
+};
+
+struct SslCache *CreateSslCache(size_t, int);
+void FreeSslCache(struct SslCache *);
+int UncacheSslSession(void *, mbedtls_ssl_session *);
+int CacheSslSession(void *, const mbedtls_ssl_session *);
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_NET_HTTPS_SSLCACHE_H_ */