freebsd-dev/usr.bin/proccontrol/proccontrol.c
Konstantin Belousov fa50a3552d Implement Address Space Layout Randomization (ASLR)
With this change, randomization can be enabled for all non-fixed
mappings.  It means that the base address for the mapping is selected
with a guaranteed amount of entropy (bits). If the mapping was
requested to be superpage aligned, the randomization honours the
superpage attributes.

Although the value of ASLR is diminshing over time as exploit authors
work out simple ASLR bypass techniques, it elimintates the trivial
exploitation of certain vulnerabilities, at least in theory.  This
implementation is relatively small and happens at the correct
architectural level.  Also, it is not expected to introduce
regressions in existing cases when turned off (default for now), or
cause any significant maintaince burden.

The randomization is done on a best-effort basis - that is, the
allocator falls back to a first fit strategy if fragmentation prevents
entropy injection.  It is trivial to implement a strong mode where
failure to guarantee the requested amount of entropy results in
mapping request failure, but I do not consider that to be usable.

I have not fine-tuned the amount of entropy injected right now. It is
only a quantitive change that will not change the implementation.  The
current amount is controlled by aslr_pages_rnd.

To not spoil coalescing optimizations, to reduce the page table
fragmentation inherent to ASLR, and to keep the transient superpage
promotion for the malloced memory, locality clustering is implemented
for anonymous private mappings, which are automatically grouped until
fragmentation kicks in.  The initial location for the anon group range
is, of course, randomized.  This is controlled by vm.cluster_anon,
enabled by default.

The default mode keeps the sbrk area unpopulated by other mappings,
but this can be turned off, which gives much more breathing bits on
architectures with small address space, such as i386.  This is tied
with the question of following an application's hint about the mmap(2)
base address. Testing shows that ignoring the hint does not affect the
function of common applications, but I would expect more demanding
code could break. By default sbrk is preserved and mmap hints are
satisfied, which can be changed by using the
kern.elf{32,64}.aslr.honor_sbrk sysctl.

ASLR is enabled on per-ABI basis, and currently it is only allowed on
FreeBSD native i386 and amd64 (including compat 32bit) ABIs.  Support
for additional architectures will be added after further testing.

Both per-process and per-image controls are implemented:
- procctl(2) adds PROC_ASLR_CTL/PROC_ASLR_STATUS;
- NT_FREEBSD_FCTL_ASLR_DISABLE feature control note bit makes it possible
  to force ASLR off for the given binary.  (A tool to edit the feature
  control note is in development.)
Global controls are:
- kern.elf{32,64}.aslr.enable - for non-fixed mappings done by mmap(2);
- kern.elf{32,64}.aslr.pie_enable - for PIE image activation mappings;
- kern.elf{32,64}.aslr.honor_sbrk - allow to use sbrk area for mmap(2);
- vm.cluster_anon - enables anon mapping clustering.

PR:	208580 (exp runs)
Exp-runs done by:	antoine
Reviewed by:	markj (previous version)
Discussed with:	emaste
Tested by:	pho
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D5603
2019-02-10 17:19:45 +00:00

209 lines
4.8 KiB
C

/*-
* Copyright (c) 2016 The FreeBSD Foundation
* All rights reserved.
*
* This software was developed by Konstantin Belousov <kib@FreeBSD.org>
* under sponsorship from the FreeBSD Foundation.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS 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 ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/procctl.h>
#include <err.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
enum {
MODE_ASLR,
MODE_INVALID,
MODE_TRACE,
MODE_TRAPCAP,
};
static pid_t
str2pid(const char *str)
{
pid_t res;
char *tail;
res = strtol(str, &tail, 0);
if (*tail != '\0') {
warnx("non-numeric pid");
return (-1);
}
return (res);
}
static void __dead2
usage(void)
{
fprintf(stderr, "Usage: proccontrol -m (aslr|trace|trapcap) [-q] "
"[-s (enable|disable)] [-p pid | command]\n");
exit(1);
}
int
main(int argc, char *argv[])
{
int arg, ch, error, mode;
pid_t pid;
bool enable, do_command, query;
mode = MODE_INVALID;
enable = true;
pid = -1;
query = false;
while ((ch = getopt(argc, argv, "m:qs:p:")) != -1) {
switch (ch) {
case 'm':
if (strcmp(optarg, "aslr") == 0)
mode = MODE_ASLR;
else if (strcmp(optarg, "trace") == 0)
mode = MODE_TRACE;
else if (strcmp(optarg, "trapcap") == 0)
mode = MODE_TRAPCAP;
else
usage();
break;
case 's':
if (strcmp(optarg, "enable") == 0)
enable = true;
else if (strcmp(optarg, "disable") == 0)
enable = false;
else
usage();
break;
case 'p':
pid = str2pid(optarg);
break;
case 'q':
query = true;
break;
case '?':
default:
usage();
break;
}
}
argc -= optind;
argv += optind;
do_command = argc != 0;
if (do_command) {
if (pid != -1 || query)
usage();
pid = getpid();
} else if (pid == -1) {
pid = getpid();
}
if (query) {
switch (mode) {
case MODE_ASLR:
error = procctl(P_PID, pid, PROC_ASLR_STATUS, &arg);
break;
case MODE_TRACE:
error = procctl(P_PID, pid, PROC_TRACE_STATUS, &arg);
break;
case MODE_TRAPCAP:
error = procctl(P_PID, pid, PROC_TRAPCAP_STATUS, &arg);
break;
default:
usage();
break;
}
if (error != 0)
err(1, "procctl status");
switch (mode) {
case MODE_ASLR:
switch (arg & ~PROC_ASLR_ACTIVE) {
case PROC_ASLR_FORCE_ENABLE:
printf("force enabled");
break;
case PROC_ASLR_FORCE_DISABLE:
printf("force disabled");
break;
case PROC_ASLR_NOFORCE:
printf("not forced");
break;
}
if ((arg & PROC_ASLR_ACTIVE) != 0)
printf(", active\n");
else
printf(", not active\n");
break;
case MODE_TRACE:
if (arg == -1)
printf("disabled\n");
else if (arg == 0)
printf("enabled, no debugger\n");
else
printf("enabled, traced by %d\n", arg);
break;
case MODE_TRAPCAP:
switch (arg) {
case PROC_TRAPCAP_CTL_ENABLE:
printf("enabled\n");
break;
case PROC_TRAPCAP_CTL_DISABLE:
printf("disabled\n");
break;
}
break;
}
} else {
switch (mode) {
case MODE_ASLR:
arg = enable ? PROC_ASLR_FORCE_ENABLE :
PROC_ASLR_FORCE_DISABLE;
error = procctl(P_PID, pid, PROC_ASLR_CTL, &arg);
break;
case MODE_TRACE:
arg = enable ? PROC_TRACE_CTL_ENABLE :
PROC_TRACE_CTL_DISABLE;
error = procctl(P_PID, pid, PROC_TRACE_CTL, &arg);
break;
case MODE_TRAPCAP:
arg = enable ? PROC_TRAPCAP_CTL_ENABLE :
PROC_TRAPCAP_CTL_DISABLE;
error = procctl(P_PID, pid, PROC_TRAPCAP_CTL, &arg);
break;
default:
usage();
break;
}
if (error != 0)
err(1, "procctl ctl");
if (do_command) {
error = execvp(argv[0], argv);
err(1, "exec");
}
}
exit(0);
}