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NetBSD/sys/kern/kern_pax.c

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/* $NetBSD: kern_pax.c,v 1.16 2007/06/24 20:35:37 christos Exp $ */
/*-
* 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 "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/malloc.h>
#include <sys/fileassoc.h>
#include <sys/syslog.h>
#include <sys/vnode.h>
#include <sys/queue.h>
#include <sys/kauth.h>
#ifdef PAX_MPROTECT
static int pax_mprotect_enabled = 1;
static int pax_mprotect_global = PAX_MPROTECT;
specificdata_key_t pax_mprotect_key;
#endif
#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;
specificdata_key_t pax_segvguard_key;
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 void pax_segvguard_cb(void *);
#endif /* PAX_SEGVGUARD */
/* PaX internal setspecific flags */
#define PAX_MPROTECT_EXPLICIT_ENABLE (void *)0x01
#define PAX_MPROTECT_EXPLICIT_DISABLE (void *)0x02
#define PAX_SEGVGUARD_EXPLICIT_ENABLE (void *)0x03
#define PAX_SEGVGUARD_EXPLICIT_DISABLE (void *)0x04
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, "security", NULL,
NULL, 0, NULL, 0,
CTL_SECURITY, CTL_EOL);
sysctl_createv(clog, 0, &rnode, &rnode,
CTLFLAG_PERMANENT,
CTLTYPE_NODE, "pax",
SYSCTL_DESCR("PaX (exploit mitigation) features."),
NULL, 0, NULL, 0,
CTL_CREATE, CTL_EOL);
cnode = rnode;
#ifdef PAX_MPROTECT
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 */
rnode = cnode;
#ifdef PAX_SEGVGUARD
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 */
}
/*
* Initialize PaX.
*/
void
pax_init(void)
{
#ifdef PAX_SEGVGUARD
int error;
#endif /* PAX_SEGVGUARD */
#ifdef PAX_MPROTECT
proc_specific_key_create(&pax_mprotect_key, NULL);
#endif /* PAX_MPROTECT */
#ifdef PAX_SEGVGUARD
error = fileassoc_register("segvguard", pax_segvguard_cb,
&segvguard_id);
if (error) {
panic("pax_init: segvguard_id: error=%d\n", error);
}
proc_specific_key_create(&pax_segvguard_key, NULL);
#endif /* PAX_SEGVGUARD */
}
void
pax_adjust(struct lwp *l, uint32_t f)
{
#ifdef PAX_MPROTECT
if (pax_mprotect_enabled) {
if (f & ELF_NOTE_PAX_MPROTECT)
proc_setspecific(l->l_proc, pax_mprotect_key,
PAX_MPROTECT_EXPLICIT_ENABLE);
if (f & ELF_NOTE_PAX_NOMPROTECT)
proc_setspecific(l->l_proc, pax_mprotect_key,
PAX_MPROTECT_EXPLICIT_DISABLE);
}
#endif /* PAX_MPROTECT */
#ifdef PAX_SEGVGUARD
if (pax_segvguard_enabled) {
if (f & ELF_NOTE_PAX_GUARD)
proc_setspecific(l->l_proc, pax_segvguard_key,
PAX_SEGVGUARD_EXPLICIT_ENABLE);
if (f & ELF_NOTE_PAX_NOGUARD)
proc_setspecific(l->l_proc, pax_segvguard_key,
PAX_SEGVGUARD_EXPLICIT_DISABLE);
}
#endif /* PAX_SEGVGUARD */
}
#ifdef PAX_MPROTECT
void
pax_mprotect(struct lwp *l, vm_prot_t *prot, vm_prot_t *maxprot)
{
void *t;
if (!pax_mprotect_enabled)
return;
t = proc_getspecific(l->l_proc, pax_mprotect_key);
if ((pax_mprotect_global && t == PAX_MPROTECT_EXPLICIT_DISABLE) ||
(!pax_mprotect_global && t != PAX_MPROTECT_EXPLICIT_ENABLE))
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_SEGVGUARD
static void
pax_segvguard_cb(void *v)
{
struct pax_segvguard_entry *p;
struct pax_segvguard_uid_entry *up;
if (v == NULL)
return;
p = v;
while ((up = LIST_FIRST(&p->segv_uids)) != NULL) {
LIST_REMOVE(up, sue_list);
free(up, M_TEMP);
}
free(v, M_TEMP);
}
/*
* 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;
void *t;
bool have_uid;
if (!pax_segvguard_enabled)
return (0);
t = proc_getspecific(l->l_proc, pax_segvguard_key);
if ((pax_segvguard_global && t == PAX_SEGVGUARD_EXPLICIT_DISABLE) ||
(!pax_segvguard_global && t != PAX_SEGVGUARD_EXPLICIT_ENABLE))
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 = malloc(sizeof(*p), M_TEMP, M_WAITOK);
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 = malloc(sizeof(*up), M_TEMP, M_WAITOK);
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 = malloc(sizeof(*up), M_TEMP, M_WAITOK);
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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