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freebsd-dev/sys/vm/vm_unix.c
Mark Johnston 9f9c9b22ec Reimplement brk() and sbrk() to avoid the use of _end. 
Previously, libc.so would initialize its notion of the break address
using _end, a special symbol emitted by the static linker following
the bss section.  Compatibility issues between lld and ld.bfd could
cause the wrong definition of _end (libc.so's definition rather than
that of the executable) to be used, breaking the brk()/sbrk()
interface.

Avoid this problem and future interoperability issues by simply not
relying on _end.  Instead, modify the break() system call to return
the kernel's view of the current break address, and have libc
initialize its state using an extra syscall upon the first use of the
interface.  As a side effect, this appears to fix brk()/sbrk() usage
in executables run with rtld direct exec, since the kernel and libc.so
no longer maintain separate views of the process' break address.

PR:		228574
Reviewed by:	kib (previous version)
MFC after:	2 months
Differential Revision:	https://reviews.freebsd.org/D15663
2018-06-04 19:35:15 +00:00

248 lines
6.8 KiB
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/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 1988 University of Utah.
* Copyright (c) 1991, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* the Systems Programming Group of the University of Utah Computer
* Science Department.
*
* 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. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
*
* from: Utah $Hdr: vm_unix.c 1.1 89/11/07$
*
* @(#)vm_unix.c 8.1 (Berkeley) 6/11/93
*/
/*
* Traditional sbrk/grow interface to VM
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/racct.h>
#include <sys/resourcevar.h>
#include <sys/sysent.h>
#include <sys/sysproto.h>
#include <sys/systm.h>
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#ifndef _SYS_SYSPROTO_H_
struct obreak_args {
char *nsize;
};
#endif
int
sys_obreak(struct thread *td, struct obreak_args *uap)
{
#if !defined(__aarch64__) && !defined(__riscv__)
struct vmspace *vm = td->td_proc->p_vmspace;
vm_map_t map = &vm->vm_map;
vm_offset_t new, old, base;
rlim_t datalim, lmemlim, vmemlim;
int prot, rv;
int error = 0;
boolean_t do_map_wirefuture;
datalim = lim_cur(td, RLIMIT_DATA);
lmemlim = lim_cur(td, RLIMIT_MEMLOCK);
vmemlim = lim_cur(td, RLIMIT_VMEM);
do_map_wirefuture = FALSE;
new = round_page((vm_offset_t)uap->nsize);
vm_map_lock(map);
base = round_page((vm_offset_t) vm->vm_daddr);
old = base + ctob(vm->vm_dsize);
if (new > base) {
/*
* Check the resource limit, but allow a process to reduce
* its usage, even if it remains over the limit.
*/
if (new - base > datalim && new > old) {
error = ENOMEM;
goto done;
}
if (new > vm_map_max(map)) {
error = ENOMEM;
goto done;
}
} else if (new < base) {
/*
* Simply return the current break address without
* modifying any state. This is an ad-hoc interface
* used by libc to determine the initial break address,
* avoiding a dependency on magic features in the system
* linker.
*/
new = old;
goto done;
}
if (new > old) {
if (!old_mlock && map->flags & MAP_WIREFUTURE) {
if (ptoa(pmap_wired_count(map->pmap)) +
(new - old) > lmemlim) {
error = ENOMEM;
goto done;
}
}
if (map->size + (new - old) > vmemlim) {
error = ENOMEM;
goto done;
}
#ifdef RACCT
if (racct_enable) {
PROC_LOCK(td->td_proc);
error = racct_set(td->td_proc, RACCT_DATA, new - base);
if (error != 0) {
PROC_UNLOCK(td->td_proc);
error = ENOMEM;
goto done;
}
error = racct_set(td->td_proc, RACCT_VMEM,
map->size + (new - old));
if (error != 0) {
racct_set_force(td->td_proc, RACCT_DATA,
old - base);
PROC_UNLOCK(td->td_proc);
error = ENOMEM;
goto done;
}
if (!old_mlock && map->flags & MAP_WIREFUTURE) {
error = racct_set(td->td_proc, RACCT_MEMLOCK,
ptoa(pmap_wired_count(map->pmap)) +
(new - old));
if (error != 0) {
racct_set_force(td->td_proc, RACCT_DATA,
old - base);
racct_set_force(td->td_proc, RACCT_VMEM,
map->size);
PROC_UNLOCK(td->td_proc);
error = ENOMEM;
goto done;
}
}
PROC_UNLOCK(td->td_proc);
}
#endif
prot = VM_PROT_RW;
#ifdef COMPAT_FREEBSD32
#if defined(__amd64__)
if (i386_read_exec && SV_PROC_FLAG(td->td_proc, SV_ILP32))
prot |= VM_PROT_EXECUTE;
#endif
#endif
rv = vm_map_insert(map, NULL, 0, old, new, prot, VM_PROT_ALL, 0);
if (rv != KERN_SUCCESS) {
#ifdef RACCT
if (racct_enable) {
PROC_LOCK(td->td_proc);
racct_set_force(td->td_proc,
RACCT_DATA, old - base);
racct_set_force(td->td_proc,
RACCT_VMEM, map->size);
if (!old_mlock && map->flags & MAP_WIREFUTURE) {
racct_set_force(td->td_proc,
RACCT_MEMLOCK,
ptoa(pmap_wired_count(map->pmap)));
}
PROC_UNLOCK(td->td_proc);
}
#endif
error = ENOMEM;
goto done;
}
vm->vm_dsize += btoc(new - old);
/*
* Handle the MAP_WIREFUTURE case for legacy applications,
* by marking the newly mapped range of pages as wired.
* We are not required to perform a corresponding
* vm_map_unwire() before vm_map_delete() below, as
* it will forcibly unwire the pages in the range.
*
* XXX If the pages cannot be wired, no error is returned.
*/
if ((map->flags & MAP_WIREFUTURE) == MAP_WIREFUTURE) {
if (bootverbose)
printf("obreak: MAP_WIREFUTURE set\n");
do_map_wirefuture = TRUE;
}
} else if (new < old) {
rv = vm_map_delete(map, new, old);
if (rv != KERN_SUCCESS) {
error = ENOMEM;
goto done;
}
vm->vm_dsize -= btoc(old - new);
#ifdef RACCT
if (racct_enable) {
PROC_LOCK(td->td_proc);
racct_set_force(td->td_proc, RACCT_DATA, new - base);
racct_set_force(td->td_proc, RACCT_VMEM, map->size);
if (!old_mlock && map->flags & MAP_WIREFUTURE) {
racct_set_force(td->td_proc, RACCT_MEMLOCK,
ptoa(pmap_wired_count(map->pmap)));
}
PROC_UNLOCK(td->td_proc);
}
#endif
}
done:
vm_map_unlock(map);
if (do_map_wirefuture)
(void) vm_map_wire(map, old, new,
VM_MAP_WIRE_USER|VM_MAP_WIRE_NOHOLES);
if (error == 0)
td->td_retval[0] = new;
return (error);
#else /* defined(__aarch64__) || defined(__riscv__) */
return (ENOSYS);
#endif /* defined(__aarch64__) || defined(__riscv__) */
}
#ifdef COMPAT_FREEBSD11
int
freebsd11_vadvise(struct thread *td, struct freebsd11_vadvise_args *uap)
{
return (EINVAL);
}
#endif
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