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NetBSD/sys/kern/kern_pax.c

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/* $NetBSD: kern_pax.c,v 1.31 2015/08/04 18:28:09 maxv Exp $ */
/*
* Copyright (c) 2015 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Maxime Villard.
*
* 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
*/
/*
* Copyright (c) 2006 Elad Efrat <elad@NetBSD.org>
* All rights reserved.
*
* 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.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 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>
__KERNEL_RCSID(0, "$NetBSD: kern_pax.c,v 1.31 2015/08/04 18:28:09 maxv Exp $");
#include "opt_pax.h"
#include <sys/param.h>
#include <sys/proc.h>
#include <sys/exec_elf.h>
#include <sys/pax.h>
#include <sys/sysctl.h>
#include <sys/kmem.h>
#include <sys/fileassoc.h>
#include <sys/syslog.h>
#include <sys/vnode.h>
#include <sys/queue.h>
#include <sys/kauth.h>
#include <sys/cprng.h>
#ifdef PAX_ASLR_DEBUG
#define PAX_DPRINTF(_fmt, args...) uprintf("%s: " _fmt "\n", __func__, ##args)
#else
#define PAX_DPRINTF(_fmt, args...) do {} while (/*CONSTCOND*/0)
#endif
#ifdef PAX_ASLR
#include <sys/mman.h>
#include <sys/exec.h>
int pax_aslr_enabled = 1;
int pax_aslr_global = PAX_ASLR;
#ifndef PAX_ASLR_DELTA_MMAP_LSB
#define PAX_ASLR_DELTA_MMAP_LSB PGSHIFT
#endif
#ifndef PAX_ASLR_DELTA_MMAP_LEN
#define PAX_ASLR_DELTA_MMAP_LEN ((sizeof(void *) * NBBY) / 2)
#endif
#ifndef PAX_ASLR_DELTA_STACK_LSB
#define PAX_ASLR_DELTA_STACK_LSB PGSHIFT
#endif
#ifndef PAX_ASLR_DELTA_STACK_LEN
#define PAX_ASLR_DELTA_STACK_LEN 12
#endif
static bool pax_aslr_elf_flags_active(uint32_t);
#endif /* PAX_ASLR */
#ifdef PAX_MPROTECT
static int pax_mprotect_enabled = 1;
static int pax_mprotect_global = PAX_MPROTECT;
static bool pax_mprotect_elf_flags_active(uint32_t);
#endif /* PAX_MPROTECT */
#ifdef PAX_SEGVGUARD
#ifndef PAX_SEGVGUARD_EXPIRY
#define PAX_SEGVGUARD_EXPIRY (2 * 60)
#endif
#ifndef PAX_SEGVGUARD_SUSPENSION
#define PAX_SEGVGUARD_SUSPENSION (10 * 60)
#endif
#ifndef PAX_SEGVGUARD_MAXCRASHES
#define PAX_SEGVGUARD_MAXCRASHES 5
#endif
static int pax_segvguard_enabled = 1;
static int pax_segvguard_global = PAX_SEGVGUARD;
static int pax_segvguard_expiry = PAX_SEGVGUARD_EXPIRY;
static int pax_segvguard_suspension = PAX_SEGVGUARD_SUSPENSION;
static int pax_segvguard_maxcrashes = PAX_SEGVGUARD_MAXCRASHES;
static fileassoc_t segvguard_id;
struct pax_segvguard_uid_entry {
uid_t sue_uid;
size_t sue_ncrashes;
time_t sue_expiry;
time_t sue_suspended;
LIST_ENTRY(pax_segvguard_uid_entry) sue_list;
};
struct pax_segvguard_entry {
LIST_HEAD(, pax_segvguard_uid_entry) segv_uids;
};
static bool pax_segvguard_elf_flags_active(uint32_t);
static void pax_segvguard_cleanup_cb(void *);
#endif /* PAX_SEGVGUARD */
SYSCTL_SETUP(sysctl_security_pax_setup, "sysctl security.pax setup")
{
const struct sysctlnode *rnode = NULL, *cnode;
sysctl_createv(clog, 0, NULL, &rnode,
CTLFLAG_PERMANENT,
CTLTYPE_NODE, "pax",
SYSCTL_DESCR("PaX (exploit mitigation) features."),
NULL, 0, NULL, 0,
CTL_SECURITY, CTL_CREATE, CTL_EOL);
cnode = rnode;
#ifdef PAX_MPROTECT
rnode = cnode;
sysctl_createv(clog, 0, &rnode, &rnode,
CTLFLAG_PERMANENT,
CTLTYPE_NODE, "mprotect",
SYSCTL_DESCR("mprotect(2) W^X restrictions."),
NULL, 0, NULL, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
CTLTYPE_INT, "enabled",
SYSCTL_DESCR("Restrictions enabled."),
NULL, 0, &pax_mprotect_enabled, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
CTLTYPE_INT, "global",
SYSCTL_DESCR("When enabled, unless explicitly "
"specified, apply restrictions to "
"all processes."),
NULL, 0, &pax_mprotect_global, 0,
CTL_CREATE, CTL_EOL);
#endif /* PAX_MPROTECT */
#ifdef PAX_SEGVGUARD
rnode = cnode;
sysctl_createv(clog, 0, &rnode, &rnode,
CTLFLAG_PERMANENT,
CTLTYPE_NODE, "segvguard",
SYSCTL_DESCR("PaX segvguard."),
NULL, 0, NULL, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
CTLTYPE_INT, "enabled",
SYSCTL_DESCR("segvguard enabled."),
NULL, 0, &pax_segvguard_enabled, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
CTLTYPE_INT, "global",
SYSCTL_DESCR("segvguard all programs."),
NULL, 0, &pax_segvguard_global, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
CTLTYPE_INT, "expiry_timeout",
SYSCTL_DESCR("Entry expiry timeout (in seconds)."),
NULL, 0, &pax_segvguard_expiry, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
CTLTYPE_INT, "suspend_timeout",
SYSCTL_DESCR("Entry suspension timeout (in seconds)."),
NULL, 0, &pax_segvguard_suspension, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
CTLTYPE_INT, "max_crashes",
SYSCTL_DESCR("Max number of crashes before expiry."),
NULL, 0, &pax_segvguard_maxcrashes, 0,
CTL_CREATE, CTL_EOL);
#endif /* PAX_SEGVGUARD */
#ifdef PAX_ASLR
rnode = cnode;
sysctl_createv(clog, 0, &rnode, &rnode,
CTLFLAG_PERMANENT,
CTLTYPE_NODE, "aslr",
SYSCTL_DESCR("Address Space Layout Randomization."),
NULL, 0, NULL, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
CTLTYPE_INT, "enabled",
SYSCTL_DESCR("Restrictions enabled."),
NULL, 0, &pax_aslr_enabled, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
CTLTYPE_INT, "global",
SYSCTL_DESCR("When enabled, unless explicitly "
"specified, apply to all processes."),
NULL, 0, &pax_aslr_global, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
CTLTYPE_INT, "mmap_len",
SYSCTL_DESCR("Number of bits randomized for "
"mmap(2) calls."),
NULL, PAX_ASLR_DELTA_MMAP_LEN, NULL, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
CTLTYPE_INT, "stack_len",
SYSCTL_DESCR("Number of bits randomized for "
"the stack."),
NULL, PAX_ASLR_DELTA_STACK_LEN, NULL, 0,
CTL_CREATE, CTL_EOL);
sysctl_createv(clog, 0, &rnode, NULL,
CTLFLAG_PERMANENT|CTLFLAG_IMMEDIATE,
CTLTYPE_INT, "exec_len",
SYSCTL_DESCR("Number of bits randomized for "
"the PIE exec base."),
NULL, PAX_ASLR_DELTA_EXEC_LEN, NULL, 0,
CTL_CREATE, CTL_EOL);
#endif /* PAX_ASLR */
}
/*
* Initialize PaX.
*/
void
pax_init(void)
{
#ifdef PAX_SEGVGUARD
int error;
error = fileassoc_register("segvguard", pax_segvguard_cleanup_cb,
&segvguard_id);
if (error) {
panic("pax_init: segvguard_id: error=%d\n", error);
}
#endif /* PAX_SEGVGUARD */
}
void
pax_setup_elf_flags(struct lwp *l, uint32_t elf_flags)
{
uint32_t flags = 0;
#ifdef PAX_ASLR
if (pax_aslr_elf_flags_active(elf_flags)) {
flags |= P_PAX_ASLR;
}
#endif
#ifdef PAX_MPROTECT
if (pax_mprotect_elf_flags_active(elf_flags)) {
flags |= P_PAX_MPROTECT;
}
#endif
#ifdef PAX_SEGVGUARD
if (pax_segvguard_elf_flags_active(elf_flags)) {
flags |= P_PAX_GUARD;
}
#endif
l->l_proc->p_pax = flags;
}
#if defined(PAX_MPROTECT) || defined(PAX_SEGVGUARD) || defined(PAX_ASLR)
static inline bool
pax_flags_active(uint32_t flags, uint32_t opt)
{
if (!(flags & opt))
return false;
return true;
}
#endif /* PAX_MPROTECT || PAX_SEGVGUARD || PAX_ASLR */
#ifdef PAX_MPROTECT
static bool
pax_mprotect_elf_flags_active(uint32_t flags)
{
if (!pax_mprotect_enabled)
return false;
if (pax_mprotect_global && (flags & ELF_NOTE_PAX_NOMPROTECT) != 0) {
/* Mprotect explicitly disabled */
return false;
}
if (!pax_mprotect_global && (flags & ELF_NOTE_PAX_MPROTECT) == 0) {
/* Mprotect not requested */
return false;
}
return true;
}
void
pax_mprotect(struct lwp *l, vm_prot_t *prot, vm_prot_t *maxprot)
{
uint32_t flags;
flags = l->l_proc->p_pax;
if (!pax_flags_active(flags, P_PAX_MPROTECT))
return;
if ((*prot & (VM_PROT_WRITE|VM_PROT_EXECUTE)) != VM_PROT_EXECUTE) {
*prot &= ~VM_PROT_EXECUTE;
*maxprot &= ~VM_PROT_EXECUTE;
} else {
*prot &= ~VM_PROT_WRITE;
*maxprot &= ~VM_PROT_WRITE;
}
}
#endif /* PAX_MPROTECT */
#ifdef PAX_ASLR
static bool
pax_aslr_elf_flags_active(uint32_t flags)
{
if (!pax_aslr_enabled)
return false;
if (pax_aslr_global && (flags & ELF_NOTE_PAX_NOASLR) != 0) {
/* ASLR explicitly disabled */
return false;
}
if (!pax_aslr_global && (flags & ELF_NOTE_PAX_ASLR) == 0) {
/* ASLR not requested */
return false;
}
return true;
}
bool
pax_aslr_active(struct lwp *l)
{
return pax_flags_active(l->l_proc->p_pax, P_PAX_ASLR);
}
void
pax_aslr_init_vm(struct lwp *l, struct vmspace *vm)
{
if (!pax_aslr_active(l))
return;
vm->vm_aslr_delta_mmap = PAX_ASLR_DELTA(cprng_fast32(),
PAX_ASLR_DELTA_MMAP_LSB, PAX_ASLR_DELTA_MMAP_LEN);
}
void
pax_aslr_mmap(struct lwp *l, vaddr_t *addr, vaddr_t orig_addr, int f)
{
if (!pax_aslr_active(l))
return;
if (!(f & MAP_FIXED) && ((orig_addr == 0) || !(f & MAP_ANON))) {
PAX_DPRINTF("applying to 0x%lx orig_addr=0x%lx f=%x",
(unsigned long)*addr, (unsigned long)orig_addr, f);
if (!(l->l_proc->p_vmspace->vm_map.flags & VM_MAP_TOPDOWN))
*addr += l->l_proc->p_vmspace->vm_aslr_delta_mmap;
else
*addr -= l->l_proc->p_vmspace->vm_aslr_delta_mmap;
PAX_DPRINTF("result 0x%lx", *addr);
} else {
PAX_DPRINTF("not applying to 0x%lx orig_addr=0x%lx f=%x",
(unsigned long)*addr, (unsigned long)orig_addr, f);
}
}
void
pax_aslr_stack(struct lwp *l, struct exec_package *epp, u_long *max_stack_size)
{
if (!pax_aslr_active(l))
return;
u_long d = PAX_ASLR_DELTA(cprng_fast32(),
PAX_ASLR_DELTA_STACK_LSB,
PAX_ASLR_DELTA_STACK_LEN);
PAX_DPRINTF("stack 0x%lx d=0x%lx 0x%lx",
epp->ep_minsaddr, d, epp->ep_minsaddr - d);
epp->ep_minsaddr -= d;
*max_stack_size -= d;
if (epp->ep_ssize > *max_stack_size)
epp->ep_ssize = *max_stack_size;
}
#endif /* PAX_ASLR */
#ifdef PAX_SEGVGUARD
static bool
pax_segvguard_elf_flags_active(uint32_t flags)
{
if (!pax_segvguard_enabled)
return false;
if (pax_segvguard_global && (flags & ELF_NOTE_PAX_NOGUARD) != 0) {
/* Segvguard explicitly disabled */
return false;
}
if (!pax_segvguard_global && (flags & ELF_NOTE_PAX_GUARD) == 0) {
/* Segvguard not requested */
return false;
}
return true;
}
static void
pax_segvguard_cleanup_cb(void *v)
{
struct pax_segvguard_entry *p = v;
struct pax_segvguard_uid_entry *up;
if (p == NULL) {
return;
}
while ((up = LIST_FIRST(&p->segv_uids)) != NULL) {
LIST_REMOVE(up, sue_list);
kmem_free(up, sizeof(*up));
}
kmem_free(p, sizeof(*p));
}
/*
* Called when a process of image vp generated a segfault.
*/
int
pax_segvguard(struct lwp *l, struct vnode *vp, const char *name,
bool crashed)
{
struct pax_segvguard_entry *p;
struct pax_segvguard_uid_entry *up;
struct timeval tv;
uid_t uid;
uint32_t flags;
bool have_uid;
flags = l->l_proc->p_pax;
if (!pax_flags_active(flags, P_PAX_GUARD))
return 0;
if (vp == NULL)
return EFAULT;
/* Check if we already monitor the file. */
p = fileassoc_lookup(vp, segvguard_id);
/* Fast-path if starting a program we don't know. */
if (p == NULL && !crashed)
return 0;
microtime(&tv);
/*
* If a program we don't know crashed, we need to create a new entry
* for it.
*/
if (p == NULL) {
p = kmem_alloc(sizeof(*p), KM_SLEEP);
fileassoc_add(vp, segvguard_id, p);
LIST_INIT(&p->segv_uids);
/*
* Initialize a new entry with "crashes so far" of 1.
* The expiry time is when we purge the entry if it didn't
* reach the limit.
*/
up = kmem_alloc(sizeof(*up), KM_SLEEP);
up->sue_uid = kauth_cred_getuid(l->l_cred);
up->sue_ncrashes = 1;
up->sue_expiry = tv.tv_sec + pax_segvguard_expiry;
up->sue_suspended = 0;
LIST_INSERT_HEAD(&p->segv_uids, up, sue_list);
return 0;
}
/*
* A program we "know" either executed or crashed again.
* See if it's a culprit we're familiar with.
*/
uid = kauth_cred_getuid(l->l_cred);
have_uid = false;
LIST_FOREACH(up, &p->segv_uids, sue_list) {
if (up->sue_uid == uid) {
have_uid = true;
break;
}
}
/*
* It's someone else. Add an entry for him if we crashed.
*/
if (!have_uid) {
if (crashed) {
up = kmem_alloc(sizeof(*up), KM_SLEEP);
up->sue_uid = uid;
up->sue_ncrashes = 1;
up->sue_expiry = tv.tv_sec + pax_segvguard_expiry;
up->sue_suspended = 0;
LIST_INSERT_HEAD(&p->segv_uids, up, sue_list);
}
return 0;
}
if (crashed) {
/* Check if timer on previous crashes expired first. */
if (up->sue_expiry < tv.tv_sec) {
log(LOG_INFO, "PaX Segvguard: [%s] Suspension"
" expired.\n", name ? name : "unknown");
up->sue_ncrashes = 1;
up->sue_expiry = tv.tv_sec + pax_segvguard_expiry;
up->sue_suspended = 0;
return 0;
}
up->sue_ncrashes++;
if (up->sue_ncrashes >= pax_segvguard_maxcrashes) {
log(LOG_ALERT, "PaX Segvguard: [%s] Suspending "
"execution for %d seconds after %zu crashes.\n",
name ? name : "unknown", pax_segvguard_suspension,
up->sue_ncrashes);
/* Suspend this program for a while. */
up->sue_suspended = tv.tv_sec + pax_segvguard_suspension;
up->sue_ncrashes = 0;
up->sue_expiry = 0;
}
} else {
/* Are we supposed to be suspended? */
if (up->sue_suspended > tv.tv_sec) {
log(LOG_ALERT, "PaX Segvguard: [%s] Preventing "
"execution due to repeated segfaults.\n", name ?
name : "unknown");
return EPERM;
}
}
return 0;
}
#endif /* PAX_SEGVGUARD */
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