/*      $NetBSD: kern_pax.c,v 1.65 2026/01/04 01:36:27 riastradh Exp $  */

/*
 * Copyright (c) 2015, 2020 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 1.65 2026/01/04 01:36:27 riastradh Exp $");

#include "opt_pax.h"

#include <sys/param.h>
#include <sys/types.h>

#include <sys/bitops.h>
#include <sys/cprng.h>
#include <sys/exec.h>
#include <sys/exec_elf.h>
#include <sys/kauth.h>
#include <sys/kmem.h>
#include <sys/mman.h>
#include <sys/pax.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/sdt.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/vnode.h>

#ifdef PAX_ASLR_DEBUG
#define PAX_DPRINTF(_fmt, args...) \
        do if (pax_aslr_debug) uprintf("%s: " _fmt "\n", __func__, ##args); \
        while (/*CONSTCOND*/0)
#else
#define PAX_DPRINTF(_fmt, args...)      do {} while (/*CONSTCOND*/0)
#endif

#ifdef PAX_ASLR
#include <sys/mman.h>
#include <sys/resourcevar.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_MMAP_LEN32
#define PAX_ASLR_DELTA_MMAP_LEN32       ((sizeof(uint32_t) * 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        ((sizeof(void *) * NBBY) / 4)
#endif
#ifndef PAX_ASLR_DELTA_STACK_LEN32
#define PAX_ASLR_DELTA_STACK_LEN32      ((sizeof(uint32_t) * NBBY) / 4)
#endif
#define PAX_ASLR_MAX_STACK_WASTE        8

#ifdef PAX_ASLR_DEBUG
int pax_aslr_debug;
/* flag set means disable */
int pax_aslr_flags;
uint32_t pax_aslr_rand;
#define PAX_ASLR_STACK          0x01
#define PAX_ASLR_STACK_GAP      0x02
#define PAX_ASLR_MMAP           0x04
#define PAX_ASLR_EXEC_OFFSET    0x08
#define PAX_ASLR_RTLD_OFFSET    0x10
#define PAX_ASLR_FIXED          0x20
#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 int pax_mprotect_ptrace = 1;
static bool pax_mprotect_elf_flags_active(uint32_t);
#endif /* PAX_MPROTECT */
#ifdef PAX_MPROTECT_DEBUG
int pax_mprotect_debug;
#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;

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);
#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);
        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "ptrace",
                       SYSCTL_DESCR("When enabled, allow ptrace(2) to "
                            "override mprotect permissions on traced "
                            "processes"),
                       NULL, 0, &pax_mprotect_ptrace, 0,
                       CTL_CREATE, CTL_EOL);
#ifdef PAX_MPROTECT_DEBUG
        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "debug",
                       SYSCTL_DESCR("print mprotect changes."),
                       NULL, 0, &pax_mprotect_debug, 0,
                       CTL_CREATE, CTL_EOL);
#endif
#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);
#ifdef PAX_ASLR_DEBUG
        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "debug",
                       SYSCTL_DESCR("Print ASLR selected addresses."),
                       NULL, 0, &pax_aslr_debug, 0,
                       CTL_CREATE, CTL_EOL);
        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "flags",
                       SYSCTL_DESCR("Disable/Enable select ASLR features."),
                       NULL, 0, &pax_aslr_flags, 0,
                       CTL_CREATE, CTL_EOL);
        sysctl_createv(clog, 0, &rnode, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "rand",
                       SYSCTL_DESCR("Use the given fixed random value"),
                       NULL, 0, &pax_aslr_rand, 0,
                       CTL_CREATE, CTL_EOL);
#endif
        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_ASLR
        /* Adjust maximum stack by the size we can consume for ASLR */
        maxsmap = MAXSSIZ - (MAXSSIZ / PAX_ASLR_MAX_STACK_WASTE);
        // XXX: compat32 is not handled.
#endif
}

void
pax_set_flags(struct exec_package *epp, struct proc *p)
{
        p->p_pax = epp->ep_pax_flags;

#ifdef PAX_MPROTECT
        if (pax_mprotect_ptrace == 0)
                return;
        /*
         * If we are running under the debugger, turn off MPROTECT so
         * the debugger can insert/delete breakpoints
         */
        if (p->p_slflag & PSL_TRACED)
                p->p_pax &= ~P_PAX_MPROTECT;
#endif
}

void
pax_setup_elf_flags(struct exec_package *epp, 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

        epp->ep_pax_flags = 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;
}

vm_prot_t
pax_mprotect_maxprotect(
#ifdef PAX_MPROTECT_DEBUG
    const char *file, size_t line,
#endif
    struct lwp *l, vm_prot_t active, vm_prot_t extra, vm_prot_t maxprot)
{
        uint32_t flags;

        flags = l->l_proc->p_pax;
        if (!pax_flags_active(flags, P_PAX_MPROTECT))
                return maxprot;

        return (active|extra) & maxprot;
}

int
pax_mprotect_validate(
#ifdef PAX_MPROTECT_DEBUG
    const char *file, size_t line,
#endif
    struct lwp *l, vm_prot_t prot)
{
        uint32_t flags;

        flags = l->l_proc->p_pax;
        if (!pax_flags_active(flags, P_PAX_MPROTECT))
                return 0;

        if ((prot & (VM_PROT_WRITE|VM_PROT_EXECUTE)) ==
            (VM_PROT_WRITE|VM_PROT_EXECUTE)) {
#ifdef PAX_MPROTECT_DEBUG
                struct proc *p = l->l_proc;

                if (pax_mprotect_debug)
                        printf("%s: %s,%zu: %d.%d (%s): WX rejected\n",
                            __func__, file, line,
                            p->p_pid, l->l_lid, p->p_comm);
#endif
                return SET_ERROR(EACCES);
        }
        return 0;
}

/*
 * Bypass MPROTECT for traced processes
 */
int
pax_mprotect_prot(struct lwp *l)
{
        uint32_t flags;

        flags = l->l_proc->p_pax;
        if (!pax_flags_active(flags, P_PAX_MPROTECT))
                return 0;
        if (pax_mprotect_ptrace < 2)
                return 0;
        return UVM_EXTRACT_PROT_ALL;
}


#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;
}

static bool
pax_aslr_epp_active(struct exec_package *epp)
{
        if (__predict_false((epp->ep_flags & (EXEC_32|EXEC_TOPDOWN_VM)) == 0))
                return false;
        return pax_flags_active(epp->ep_pax_flags, P_PAX_ASLR);
}

static 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, struct exec_package *ep)
{
        if (!pax_aslr_active(l))
                return;

        if (__predict_false((ep->ep_flags & (EXEC_32|EXEC_TOPDOWN_VM)) == 0))
                return;

#ifdef PAX_ASLR_DEBUG
        if (pax_aslr_flags & PAX_ASLR_MMAP)
                return;
#endif

        uint32_t len = (ep->ep_flags & EXEC_32) ?
            PAX_ASLR_DELTA_MMAP_LEN32 : PAX_ASLR_DELTA_MMAP_LEN;

        uint32_t rand = cprng_fast32();
#ifdef PAX_ASLR_DEBUG
        if (pax_aslr_flags & PAX_ASLR_FIXED)
                rand = pax_aslr_rand;
#endif
        vm->vm_aslr_delta_mmap = PAX_ASLR_DELTA(rand,
            PAX_ASLR_DELTA_MMAP_LSB, len);

        PAX_DPRINTF("delta_mmap=%#jx/%u",
            (uintmax_t)vm->vm_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;
#ifdef PAX_ASLR_DEBUG
        char buf[256];

        if (pax_aslr_flags & PAX_ASLR_MMAP)
                return;

        if (pax_aslr_debug)
                snprintb(buf, sizeof(buf), MAP_FMT, f);
        else
                buf[0] = '\0';
#endif

        if (!(f & MAP_FIXED) && ((orig_addr == 0) || !(f & MAP_ANON))) {
                PAX_DPRINTF("applying to %#jx orig_addr=%#jx f=%s",
                    (uintmax_t)*addr, (uintmax_t)orig_addr, buf);
                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 %#jx", (uintmax_t)*addr);
        } else {
                PAX_DPRINTF("not applying to %#jx orig_addr=%#jx f=%s",
                    (uintmax_t)*addr, (uintmax_t)orig_addr, buf);
        }
}

static vaddr_t
pax_aslr_offset(vaddr_t align)
{
        size_t pax_align, l2, delta;
        uint32_t rand;
        vaddr_t offset;

        pax_align = align == 0 ? PAGE_SIZE : align;
        l2 = ilog2(pax_align);

        rand = cprng_fast32();
#ifdef PAX_ASLR_DEBUG
        if (pax_aslr_flags & PAX_ASLR_FIXED)
                rand = pax_aslr_rand;
#endif

#define PAX_TRUNC(a, b) ((a) & ~((b) - 1))

        delta = PAX_ASLR_DELTA(rand, l2, PAX_ASLR_DELTA_EXEC_LEN);
        offset = PAX_TRUNC(delta, pax_align);
        offset = MAX(offset, pax_align);

        PAX_DPRINTF("rand=%#x l2=%#zx pax_align=%#zx delta=%#zx offset=%#jx",
            rand, l2, pax_align, delta, (uintmax_t)offset);

        return offset;
}

vaddr_t
pax_aslr_exec_offset(struct exec_package *epp, vaddr_t align)
{
        if (!pax_aslr_epp_active(epp))
                goto out;

#ifdef PAX_ASLR_DEBUG
        if (pax_aslr_flags & PAX_ASLR_EXEC_OFFSET)
                goto out;
#endif
        return pax_aslr_offset(align);
out:
        return MAX(align, PAGE_SIZE);
}

voff_t
pax_aslr_rtld_offset(struct exec_package *epp, vaddr_t align, int use_topdown)
{
        voff_t offset;

        if (!pax_aslr_epp_active(epp))
                return 0;

#ifdef PAX_ASLR_DEBUG
        if (pax_aslr_flags & PAX_ASLR_RTLD_OFFSET)
                return 0;
#endif
        offset = pax_aslr_offset(align);
        if (use_topdown)
                offset = -offset;

        return offset;
}

void
pax_aslr_stack(struct exec_package *epp, vsize_t *max_stack_size)
{
        if (!pax_aslr_epp_active(epp))
                return;
#ifdef PAX_ASLR_DEBUG
        if (pax_aslr_flags & PAX_ASLR_STACK)
                return;
#endif

        uint32_t len = (epp->ep_flags & EXEC_32) ?
            PAX_ASLR_DELTA_STACK_LEN32 : PAX_ASLR_DELTA_STACK_LEN;
        uint32_t rand = cprng_fast32();
#ifdef PAX_ASLR_DEBUG
        if (pax_aslr_flags & PAX_ASLR_FIXED)
                rand = pax_aslr_rand;
#endif
        u_long d = PAX_ASLR_DELTA(rand, PAX_ASLR_DELTA_STACK_LSB, len);
        d &= (*max_stack_size / PAX_ASLR_MAX_STACK_WASTE) - 1;
        u_long newminsaddr = (u_long)STACK_GROW(epp->ep_minsaddr, d);
        PAX_DPRINTF("old minsaddr=%#jx delta=%#lx new minsaddr=%#lx",
            (uintmax_t)epp->ep_minsaddr, d, newminsaddr);
        epp->ep_minsaddr = (vaddr_t)newminsaddr;
        *max_stack_size -= d;
}

uint32_t
pax_aslr_stack_gap(struct exec_package *epp)
{
        if (!pax_aslr_epp_active(epp))
                return 0;

#ifdef PAX_ASLR_DEBUG
        if (pax_aslr_flags & PAX_ASLR_STACK_GAP)
                return 0;
#endif

        uint32_t rand = cprng_fast32();
#ifdef PAX_ASLR_DEBUG
        if (pax_aslr_flags & PAX_ASLR_FIXED)
                rand = pax_aslr_rand;
#endif
        rand %= PAGE_SIZE;
        PAX_DPRINTF("stack gap=%#x\n", rand);
        return rand;
}
#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;
}

void
pax_segvguard_cleanup(struct vnode *vp)
{
        struct pax_segvguard_entry *p = vp->v_segvguard;
        struct pax_segvguard_uid_entry *up;

        if (__predict_true(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));
        vp->v_segvguard = NULL;
}

/*
 * Called when a process of image vp generated a segfault.
 *
 * => exec_lock must be held by the caller
 * => if "crashed" is true, exec_lock must be held for write
 */
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;

        KASSERT(rw_lock_held(&exec_lock));
        KASSERT(!crashed || rw_write_held(&exec_lock));

        flags = l->l_proc->p_pax;
        if (!pax_flags_active(flags, P_PAX_GUARD))
                return 0;

        if (vp == NULL)
                return SET_ERROR(EFAULT);

        /* Fast-path if starting a program we don't know. */
        if ((p = vp->v_segvguard) == 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);
                vp->v_segvguard = 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 SET_ERROR(EPERM);
                }
        }

        return 0;
}
#endif /* PAX_SEGVGUARD */