xref: /openbsd-src/lib/libc/dlfcn/init.c (revision 17423a06aac5f7ca8e40b9b2f3341b9b9f9255c6)

/*	$OpenBSD: init.c,v 1.24 2024/07/22 22:06:27 kettenis Exp $ */
/*
 * Copyright (c) 2014,2015 Philip Guenther <guenther@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */


#define _DYN_LOADER

#include <sys/types.h>
#include <sys/syscall.h>
#include <sys/timetc.h>		/* timekeep */

#ifndef PIC
#include <sys/mman.h>
#endif

#include <tib.h>
#include <limits.h>		/* NAME_MAX */
#include <link.h>
#include <stdlib.h>		/* atexit */
#include <string.h>
#include <unistd.h>

#include "init.h"

#define MAX(a,b)	(((a)>(b))?(a):(b))

#ifdef TIB_EXTRA_ALIGN
# define TIB_ALIGN	MAX(__alignof__(struct tib), TIB_EXTRA_ALIGN)
#else
# define TIB_ALIGN	__alignof__(struct tib)
#endif

/* XXX should be in an include file shared with csu */
char	***_csu_finish(char **_argv, char **_envp, void (*_cleanup)(void));

/* provide definitions for these */
int	_pagesize = 0;
struct timekeep	*_timekeep;
unsigned long	_hwcap, _hwcap2;
int	_hwcap_avail, _hwcap2_avail;

/*
 * In dynamically linked binaries environ and __progname are overridden by
 * the definitions in ld.so.
 */
char	**environ __attribute__((weak)) = NULL;
char	*__progname __attribute__((weak)) = NULL;


#ifndef PIC
struct dl_phdr_info	_static_phdr_info __relro = { .dlpi_name = "a.out" };

static inline void early_static_init(char **_argv, char **_envp);
static inline void setup_static_tib(Elf_Phdr *_phdr, int _phnum);

/* provided by the linker */
extern Elf_Ehdr __executable_start[] __attribute__((weak));
#endif /* PIC */

/* provide definitions for these */
const dl_cb *_dl_cb __relro = NULL;

int	HIDDEN(execve)(const char *, char *const *, char *const *)
	__attribute__((weak));

void _libc_preinit(int, char **, char **, dl_cb_cb *) __dso_hidden;
void
_libc_preinit(int argc, char **argv, char **envp, dl_cb_cb *cb)
{
	AuxInfo	*aux;
#ifndef PIC
	Elf_Phdr *phdr = NULL;
	int phnum = 0;

	/* static libc in a static link? */
	if (cb == NULL)
		early_static_init(argv, envp);
#endif /* !PIC */

	if (cb != NULL)
		_dl_cb = cb(DL_CB_CUR);

	/* Extract useful bits from the auxiliary vector */
	while (*envp++ != NULL)
		;
	for (aux = (void *)envp; aux->au_id != AUX_null; aux++) {
		switch (aux->au_id) {
		case AUX_hwcap:
			_hwcap = aux->au_v;
			_hwcap_avail = 1;
			break;
		case AUX_hwcap2:
			_hwcap2 = aux->au_v;
			_hwcap2_avail = 1;
			break;
		case AUX_pagesz:
			_pagesize = aux->au_v;
			break;
#ifndef PIC
		case AUX_base:
			_static_phdr_info.dlpi_addr = aux->au_v;
			break;
		case AUX_phdr:
			phdr = (void *)aux->au_v;
			break;
		case AUX_phnum:
			phnum = aux->au_v;
			break;
#endif /* !PIC */
		case AUX_openbsd_timekeep:
			if (_tc_get_timecount) {
				_timekeep = (void *)aux->au_v;
				if (_timekeep &&
				    _timekeep->tk_version != TK_VERSION)
					_timekeep = NULL;
			}
			if (issetugid() == 0 && getenv("LIBC_NOUSERTC"))
				_timekeep = NULL;
			break;
		}
	}

#ifndef PIC
	if (cb == NULL && phdr == NULL && __executable_start != NULL) {
		/*
		 * Static non-PIE processes don't get an AUX vector,
		 * so find the phdrs through the ELF header
		 */
		phdr = (void *)((char *)__executable_start +
		    __executable_start->e_phoff);
		phnum = __executable_start->e_phnum;
	}
	_static_phdr_info.dlpi_phdr = phdr;
	_static_phdr_info.dlpi_phnum = phnum;

	/* static libc in a static link? */
	if (cb == NULL)
		setup_static_tib(phdr, phnum);

	/*
	 * If a static binary has text relocations (DT_TEXT), then un-writeable
	 * segments were not made immutable by the kernel.  Textrel and RELRO
	 * changes have now been completed and permissions corrected, so these
	 * regions can become immutable.
	 */
	if (phdr) {
		int i;

		for (i = 0; i < phnum; i++) {
			if (phdr[i].p_type == PT_LOAD &&
			    (phdr[i].p_flags & PF_W) == 0)
				mimmutable((void *)(_static_phdr_info.dlpi_addr +
				    phdr[i].p_vaddr), phdr[i].p_memsz);
		}
	}
#endif /* !PIC */
}

/* ARM just had to be different... */
#ifndef __arm__
# define TYPE	"@"
#else
# define TYPE	"%"
#endif

#ifdef __LP64__
# define VALUE_ALIGN		".balign 8"
# define VALUE_DIRECTIVE	".quad"
#else
# define VALUE_ALIGN		".balign 4"
# ifdef __hppa__
   /* hppa just had to be different: func pointers prefix with 'P%' */
#  define VALUE_DIRECTIVE	".int P%"
# else
#  define VALUE_DIRECTIVE	".int"
# endif
#endif

#ifdef PIC
/*
 * Set a priority so _libc_preinit gets called before the constructor
 * on libcompiler_rt that may use elf_aux_info(3).
 */
__asm(" .section .init_array.50,\"a\","TYPE"init_array\n " \
	VALUE_ALIGN"\n "VALUE_DIRECTIVE" _libc_preinit\n .previous");
#else
__asm(" .section .preinit_array,\"a\","TYPE"preinit_array\n " \
	VALUE_ALIGN"\n "VALUE_DIRECTIVE" _libc_preinit\n .previous");
#endif

/*
 * In dynamic links, invoke ld.so's dl_clean_boot() callback, if any,
 * and register its cleanup.
 */
char ***
_csu_finish(char **argv, char **envp, void (*cleanup)(void))
{
	if (_dl_cb != NULL && _dl_cb->dl_clean_boot != NULL)
		_dl_cb->dl_clean_boot();

	if (cleanup != NULL)
		atexit(cleanup);

	return &environ;
}

#ifndef PIC
/*
 * static libc in a static link?  Then set up __progname and environ
 */
static inline void
early_static_init(char **argv, char **envp)
{
	static char progname_storage[NAME_MAX+1];

	environ = envp;

	/* set up __progname */
	if (*argv != NULL) {		/* NULL ptr if argc = 0 */
		const char *p = strrchr(*argv, '/');

		if (p == NULL)
			p = *argv;
		else
			p++;
		strlcpy(progname_storage, p, sizeof(progname_storage));
	}
	__progname = progname_storage;
}

/*
 * static TLS handling
 */
#define ELF_ROUND(x,malign)	(((x) + (malign)-1) & ~((malign)-1))

/* for static binaries, the location and size of the TLS image */
static void		*static_tls __relro;
static size_t		static_tls_fsize __relro;

size_t			_static_tls_size __relro = 0;
int			_static_tls_align __relro;
int			_static_tls_align_offset __relro;

static inline void
setup_static_tib(Elf_Phdr *phdr, int phnum)
{
	struct tib *tib;
	char *base;
	int i;

	_static_tls_align = TIB_ALIGN;
	if (phdr != NULL) {
		for (i = 0; i < phnum; i++) {
			if (phdr[i].p_type != PT_TLS)
				continue;
			if (phdr[i].p_memsz == 0)
				break;
			if (phdr[i].p_memsz < phdr[i].p_filesz)
				break;		/* invalid */
			if (phdr[i].p_align > getpagesize())
				break;		/* nope */
			_static_tls_align = MAX(phdr[i].p_align, TIB_ALIGN);
#if TLS_VARIANT == 1
			/*
			 * Variant 1 places the data after the TIB.  If the
			 * TLS alignment is larger than the TIB alignment
			 * then we may need to pad in front of the TIB to
			 * place the TLS data on the proper alignment.
			 * Example: p_align=16 sizeof(TIB)=52 align(TIB)=4
			 * - need to offset the TIB 12 bytes from the start
			 * - to place ths TLS data at offset 64
			 */
			_static_tls_size = phdr[i].p_memsz;
			_static_tls_align_offset =
			    ELF_ROUND(sizeof(struct tib), _static_tls_align) -
			    sizeof(struct tib);
#elif TLS_VARIANT == 2
			/*
			 * Variant 2 places the data before the TIB
			 * so we need to round up the size to the
			 * TLS data alignment TIB's alignment.
			 * Example A: p_memsz=24 p_align=16 align(TIB)=8
			 * - need to allocate 32 bytes for TLS as compiler
			 * - will give the first TLS symbol an offset of -32
			 * Example B: p_memsz=4 p_align=4 align(TIB)=8
			 * - need to allocate 8 bytes so that the TIB is
			 * - properly aligned
			 */
			_static_tls_size = ELF_ROUND(phdr[i].p_memsz,
			    phdr[i].p_align);
			_static_tls_align_offset = ELF_ROUND(_static_tls_size,
			    _static_tls_align) - _static_tls_size;
#endif
			if (phdr[i].p_vaddr != 0 && phdr[i].p_filesz != 0) {
				static_tls = (void *)phdr[i].p_vaddr +
				    _static_phdr_info.dlpi_addr;
				static_tls_fsize = phdr[i].p_filesz;
			}
			break;
		}
	}

	base = mmap(NULL, _static_tls_size + _static_tls_align_offset
	    + sizeof *tib, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);

	tib = _static_tls_init(base, NULL);
	tib->tib_tid = getthrid();
	TCB_SET(TIB_TO_TCB(tib));
#if ! TCB_HAVE_MD_GET
	_libc_single_tcb = TIB_TO_TCB(tib);
#endif
}

struct tib *
_static_tls_init(char *base, void *thread)
{
	struct tib *tib;

	base += _static_tls_align_offset;
# if TLS_VARIANT == 1
	tib = (struct tib *)base;
	base += sizeof(struct tib);
# elif TLS_VARIANT == 2
	tib = (struct tib *)(base + _static_tls_size);
# endif

	if (_static_tls_size) {
		if (static_tls != NULL)
			memcpy(base, static_tls, static_tls_fsize);
		memset(base + static_tls_fsize, 0,
		    _static_tls_size - static_tls_fsize);
	}

	TIB_INIT(tib, NULL, thread);
	return tib;
}
#endif /* !PIC */