freebsd-dev/lib/libc/sys/brk.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

108 lines
2.8 KiB
C

/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2018 Mark Johnston <markj@FreeBSD.org>
*
* 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/types.h>
#include <sys/syscall.h>
#include <errno.h>
#include <stdint.h>
#include <stdlib.h>
void *__sys_break(char *nsize);
static uintptr_t curbrk, minbrk;
static int curbrk_initted;
static int
initbrk(void)
{
void *newbrk;
if (!curbrk_initted) {
newbrk = __sys_break(NULL);
if (newbrk == (void *)-1)
return (-1);
curbrk = minbrk = (uintptr_t)newbrk;
curbrk_initted = 1;
}
return (0);
}
static void *
mvbrk(void *addr)
{
uintptr_t oldbrk;
if ((uintptr_t)addr < minbrk) {
/* Emulate legacy error handling in the syscall. */
errno = EINVAL;
return ((void *)-1);
}
if (__sys_break(addr) == (void *)-1)
return ((void *)-1);
oldbrk = curbrk;
curbrk = (uintptr_t)addr;
return ((void *)oldbrk);
}
int
brk(const void *addr)
{
if (initbrk() == -1)
return (-1);
if ((uintptr_t)addr < minbrk)
addr = (void *)minbrk;
return (mvbrk(__DECONST(void *, addr)) == (void *)-1 ? -1 : 0);
}
int
_brk(const void *addr)
{
if (initbrk() == -1)
return (-1);
return (mvbrk(__DECONST(void *, addr)) == (void *)-1 ? -1 : 0);
}
void *
sbrk(intptr_t incr)
{
if (initbrk() == -1)
return ((void *)-1);
if ((incr > 0 && curbrk + incr < curbrk) ||
(incr < 0 && curbrk + incr > curbrk)) {
/* Emulate legacy error handling in the syscall. */
errno = EINVAL;
return ((void *)-1);
}
return (mvbrk((void *)(curbrk + incr)));
}