glibc/elf/dl-support.c

/* Support for dynamic linking code in static libc.
   Copyright (C) 1996-2023 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

/* This file defines some things that for the dynamic linker are defined in
   rtld.c and dl-sysdep.c in ways appropriate to bootstrap dynamic linking.  */

#include <string.h>
/* Mark symbols hidden in static PIE for early self relocation to work.
   Note: string.h may have ifuncs which cannot be hidden on i686.  */
#if BUILD_PIE_DEFAULT
# pragma GCC visibility push(hidden)
#endif
#include <errno.h>
#include <libintl.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/param.h>
#include <stdint.h>
#include <ldsodefs.h>
#include <dl-machine.h>
#include <libc-lock.h>
#include <dl-cache.h>
#include <dl-procinfo.h>
#include <unsecvars.h>
#include <hp-timing.h>
#include <stackinfo.h>
#include <dl-vdso.h>
#include <dl-vdso-setup.h>
#include <dl-auxv.h>
#include <dl-find_object.h>
#include <array_length.h>
#include <dl-symbol-redir-ifunc.h>

extern char *__progname;
char **_dl_argv = &__progname;	/* This is checked for some error messages.  */

/* Name of the architecture.  */
const char *_dl_platform;
size_t _dl_platformlen;

int _dl_debug_mask;
int _dl_lazy;
int _dl_dynamic_weak;

/* If nonzero print warnings about problematic situations.  */
int _dl_verbose;

/* We never do profiling.  */
const char *_dl_profile;
const char *_dl_profile_output;

/* Names of shared object for which the RUNPATHs and RPATHs should be
   ignored.  */
const char *_dl_inhibit_rpath;

/* The map for the object we will profile.  */
struct link_map *_dl_profile_map;

/* This is the address of the last stack address ever used.  */
void *__libc_stack_end;

/* Path where the binary is found.  */
const char *_dl_origin_path;

/* Nonzero if runtime lookup should not update the .got/.plt.  */
int _dl_bind_not;

/* A dummy link map for the executable, used by dlopen to access the global
   scope.  We don't export any symbols ourselves, so this can be minimal.  */
static struct link_map _dl_main_map =
  {
    .l_name = (char *) "",
    .l_real = &_dl_main_map,
    .l_ns = LM_ID_BASE,
    .l_libname = &(struct libname_list) { .name = "", .dont_free = 1 },
    .l_searchlist =
      {
	.r_list = &(struct link_map *) { &_dl_main_map },
	.r_nlist = 1,
      },
    .l_symbolic_searchlist = { .r_list = &(struct link_map *) { NULL } },
    .l_type = lt_executable,
    .l_scope_mem = { &_dl_main_map.l_searchlist },
    .l_scope_max = (sizeof (_dl_main_map.l_scope_mem)
		    / sizeof (_dl_main_map.l_scope_mem[0])),
    .l_scope = _dl_main_map.l_scope_mem,
    .l_local_scope = { &_dl_main_map.l_searchlist },
    .l_used = 1,
    .l_tls_offset = NO_TLS_OFFSET,
    .l_serial = 1,
  };

/* Namespace information.  */
struct link_namespaces _dl_ns[DL_NNS] =
  {
    [LM_ID_BASE] =
      {
	._ns_loaded = &_dl_main_map,
	._ns_nloaded = 1,
	._ns_main_searchlist = &_dl_main_map.l_searchlist,
      }
  };
size_t _dl_nns = 1;

/* Incremented whenever something may have been added to dl_loaded. */
unsigned long long _dl_load_adds = 1;

/* Fake scope of the main application.  */
struct r_scope_elem _dl_initial_searchlist =
  {
    .r_list = &(struct link_map *) { &_dl_main_map },
    .r_nlist = 1,
  };

#ifndef HAVE_INLINED_SYSCALLS
/* Nonzero during startup.  */
int _dl_starting_up = 1;
#endif

/* Random data provided by the kernel.  */
void *_dl_random;

/* Get architecture specific initializer.  */
#include <dl-procruntime.c>
#include <dl-procinfo.c>

size_t _dl_pagesize = EXEC_PAGESIZE;

size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;

int _dl_inhibit_cache;

/* All known directories in sorted order.  */
struct r_search_path_elem *_dl_all_dirs;

/* All directories after startup.  */
struct r_search_path_elem *_dl_init_all_dirs;

/* The object to be initialized first.  */
struct link_map *_dl_initfirst;

/* Descriptor to write debug messages to.  */
int _dl_debug_fd = STDERR_FILENO;

ElfW(auxv_t) *_dl_auxv;
const ElfW(Phdr) *_dl_phdr;
size_t _dl_phnum;
uint64_t _dl_hwcap;
uint64_t _dl_hwcap2;

enum dso_sort_algorithm _dl_dso_sort_algo;

/* The value of the FPU control word the kernel will preset in hardware.  */
fpu_control_t _dl_fpu_control = _FPU_DEFAULT;

#if !HAVE_TUNABLES
/* This is not initialized to HWCAP_IMPORTANT, matching the definition
   of _dl_important_hwcaps, below, where no hwcap strings are ever
   used.  This mask is still used to mediate the lookups in the cache
   file.  Since there is no way to set this nonzero (we don't grok the
   LD_HWCAP_MASK environment variable here), there is no real point in
   setting _dl_hwcap nonzero below, but we do anyway.  */
uint64_t _dl_hwcap_mask;
#endif

/* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
 * executable but this isn't true for all platforms.  */
ElfW(Word) _dl_stack_flags = DEFAULT_STACK_PERMS;

#if PTHREAD_IN_LIBC
list_t _dl_stack_used;
list_t _dl_stack_user;
list_t _dl_stack_cache;
size_t _dl_stack_cache_actsize;
uintptr_t _dl_in_flight_stack;
int _dl_stack_cache_lock;
#else
/* If loading a shared object requires that we make the stack executable
   when it was not, we do it by calling this function.
   It returns an errno code or zero on success.  */
int (*_dl_make_stack_executable_hook) (void **) = _dl_make_stack_executable;
void (*_dl_init_static_tls) (struct link_map *) = &_dl_nothread_init_static_tls;
#endif
struct dl_scope_free_list *_dl_scope_free_list;

#ifdef NEED_DL_SYSINFO
/* Needed for improved syscall handling on at least x86/Linux.  NB: Don't
   initialize it here to avoid RELATIVE relocation in static PIE.  */
uintptr_t _dl_sysinfo;
#endif
#ifdef NEED_DL_SYSINFO_DSO
/* Address of the ELF headers in the vsyscall page.  */
const ElfW(Ehdr) *_dl_sysinfo_dso;

struct link_map *_dl_sysinfo_map;

# include "get-dynamic-info.h"
#endif
#include "setup-vdso.h"
/* Define the vDSO function pointers.  */
#include <dl-vdso-setup.c>

/* During the program run we must not modify the global data of
   loaded shared object simultanously in two threads.  Therefore we
   protect `_dl_open' and `_dl_close' in dl-close.c.

   This must be a recursive lock since the initializer function of
   the loaded object might as well require a call to this function.
   At this time it is not anymore a problem to modify the tables.  */
__rtld_lock_define_initialized_recursive (, _dl_load_lock)
/* This lock is used to keep __dl_iterate_phdr from inspecting the
   list of loaded objects while an object is added to or removed from
   that list.  */
__rtld_lock_define_initialized_recursive (, _dl_load_write_lock)
  /* This lock protects global and module specific TLS related data.
     E.g. it is held in dlopen and dlclose when GL(dl_tls_generation),
     GL(dl_tls_max_dtv_idx) or GL(dl_tls_dtv_slotinfo_list) are
     accessed and when TLS related relocations are processed for a
     module.  It was introduced to keep pthread_create accessing TLS
     state that is being set up.  */
__rtld_lock_define_initialized_recursive (, _dl_load_tls_lock)


#ifdef HAVE_AUX_VECTOR
#include <dl-parse_auxv.h>

int _dl_clktck;

void
_dl_aux_init (ElfW(auxv_t) *av)
{
#ifdef NEED_DL_SYSINFO
  /* NB: Avoid RELATIVE relocation in static PIE.  */
  GL(dl_sysinfo) = DL_SYSINFO_DEFAULT;
#endif

  _dl_auxv = av;
  dl_parse_auxv_t auxv_values;
  /* Use an explicit initialization loop here because memset may not
     be available yet.  */
  for (int i = 0; i < array_length (auxv_values); ++i)
    auxv_values[i] = 0;
  _dl_parse_auxv (av, auxv_values);

  _dl_phdr = (void*) auxv_values[AT_PHDR];
  _dl_phnum = auxv_values[AT_PHNUM];

  if (_dl_phdr == NULL)
    {
      /* Starting from binutils-2.23, the linker will define the
         magic symbol __ehdr_start to point to our own ELF header
         if it is visible in a segment that also includes the phdrs.
         So we can set up _dl_phdr and _dl_phnum even without any
         information from auxv.  */

      extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
      assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
      _dl_phdr = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
      _dl_phnum = __ehdr_start.e_phnum;
    }

  assert (_dl_phdr != NULL);
}
#endif


void
_dl_non_dynamic_init (void)
{
  _dl_main_map.l_origin = _dl_get_origin ();
  _dl_main_map.l_phdr = GL(dl_phdr);
  _dl_main_map.l_phnum = GL(dl_phnum);

  _dl_verbose = *(getenv ("LD_WARN") ?: "") == '\0' ? 0 : 1;

  /* Set up the data structures for the system-supplied DSO early,
     so they can influence _dl_init_paths.  */
  setup_vdso (NULL, NULL);

  /* With vDSO setup we can initialize the function pointers.  */
  setup_vdso_pointers ();

  /* Initialize the data structures for the search paths for shared
     objects.  */
  _dl_init_paths (getenv ("LD_LIBRARY_PATH"), "LD_LIBRARY_PATH",
		  /* No glibc-hwcaps selection support in statically
		     linked binaries.  */
		  NULL, NULL);

  /* Remember the last search directory added at startup.  */
  _dl_init_all_dirs = GL(dl_all_dirs);

  _dl_lazy = *(getenv ("LD_BIND_NOW") ?: "") == '\0';

  _dl_bind_not = *(getenv ("LD_BIND_NOT") ?: "") != '\0';

  _dl_dynamic_weak = *(getenv ("LD_DYNAMIC_WEAK") ?: "") == '\0';

  _dl_profile_output = getenv ("LD_PROFILE_OUTPUT");
  if (_dl_profile_output == NULL || _dl_profile_output[0] == '\0')
    _dl_profile_output
      = &"/var/tmp\0/var/profile"[__libc_enable_secure ? 9 : 0];

  if (__libc_enable_secure)
    {
      static const char unsecure_envvars[] =
	UNSECURE_ENVVARS
	;
      const char *cp = unsecure_envvars;

      while (cp < unsecure_envvars + sizeof (unsecure_envvars))
	{
	  __unsetenv (cp);
	  cp = strchr (cp, '\0') + 1;
	}

#if !HAVE_TUNABLES
      if (__access ("/etc/suid-debug", F_OK) != 0)
	__unsetenv ("MALLOC_CHECK_");
#endif
    }

#ifdef DL_PLATFORM_INIT
  DL_PLATFORM_INIT;
#endif

  /* Now determine the length of the platform string.  */
  if (_dl_platform != NULL)
    _dl_platformlen = strlen (_dl_platform);

  for (const ElfW(Phdr) *ph = _dl_phdr; ph < &_dl_phdr[_dl_phnum]; ++ph)
    switch (ph->p_type)
      {
      /* Check if the stack is nonexecutable.  */
      case PT_GNU_STACK:
	_dl_stack_flags = ph->p_flags;
	break;

      case PT_GNU_RELRO:
	_dl_main_map.l_relro_addr = ph->p_vaddr;
	_dl_main_map.l_relro_size = ph->p_memsz;
	break;
      }

  call_function_static_weak (_dl_find_object_init);

  /* Setup relro on the binary itself.  */
  if (_dl_main_map.l_relro_size != 0)
    _dl_protect_relro (&_dl_main_map);
}

#ifdef DL_SYSINFO_IMPLEMENTATION
DL_SYSINFO_IMPLEMENTATION
#endif

#if ENABLE_STATIC_PIE
/* Since relocation to hidden _dl_main_map causes relocation overflow on
   aarch64, a function is used to get the address of _dl_main_map.  */

struct link_map *
_dl_get_dl_main_map (void)
{
  return &_dl_main_map;
}
#endif

/* This is used by _dl_runtime_profile, not used on static code.  */
void
DL_ARCH_FIXUP_ATTRIBUTE
_dl_audit_pltexit (struct link_map *l, ElfW(Word) reloc_arg,
		   const void *inregs, void *outregs)
{
}