glibc/sysdeps/unix/sysv/linux/dl-sysdep.c

/* Dynamic linker system dependencies for Linux.
   Copyright (C) 1995-2022 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/>.  */

#include <_itoa.h>
#include <assert.h>
#include <dl-hwcap-check.h>
#include <dl-osinfo.h>
#include <dl-procinfo.h>
#include <dl-tunables.h>
#include <elf.h>
#include <entry.h>
#include <errno.h>
#include <fcntl.h>
#include <fpu_control.h>
#include <ldsodefs.h>
#include <libc-internal.h>
#include <libintl.h>
#include <not-cancel.h>
#include <stdlib.h>
#include <string.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/utsname.h>
#include <tls.h>
#include <unistd.h>

#include <dl-machine.h>

#ifdef SHARED
# include <dl-auxv.h>

extern char **_environ attribute_hidden;
extern char _end[] attribute_hidden;

/* Protect SUID program against misuse of file descriptors.  */
extern void __libc_check_standard_fds (void);

int __libc_enable_secure attribute_relro = 0;
rtld_hidden_data_def (__libc_enable_secure)
/* This variable contains the lowest stack address ever used.  */
void *__libc_stack_end attribute_relro = NULL;
rtld_hidden_data_def(__libc_stack_end)
void *_dl_random attribute_relro = NULL;

#ifndef DL_STACK_END
# define DL_STACK_END(cookie) ((void *) (cookie))
#endif

ElfW(Addr)
_dl_sysdep_start (void **start_argptr,
		  void (*dl_main) (const ElfW(Phdr) *phdr, ElfW(Word) phnum,
				   ElfW(Addr) *user_entry, ElfW(auxv_t) *auxv))
{
  const ElfW(Phdr) *phdr = NULL;
  ElfW(Word) phnum = 0;
  ElfW(Addr) user_entry;
  ElfW(auxv_t) *av;
#ifdef NEED_DL_SYSINFO
  uintptr_t new_sysinfo = 0;
#endif

  __libc_stack_end = DL_STACK_END (start_argptr);
  _dl_argc = (intptr_t) *start_argptr;
  _dl_argv = (char **) (start_argptr + 1); /* Necessary aliasing violation.  */
  _environ = _dl_argv + _dl_argc + 1;
  for (char **tmp = _environ; ; ++tmp)
    if (*tmp == NULL)
      {
	/* Another necessary aliasing violation.  */
	GLRO(dl_auxv) = (ElfW(auxv_t) *) (tmp + 1);
	break;
      }

  user_entry = (ElfW(Addr)) ENTRY_POINT;
  GLRO(dl_platform) = NULL; /* Default to nothing known about the platform.  */

  /* NB: Default to a constant CONSTANT_MINSIGSTKSZ.  */
  _Static_assert (__builtin_constant_p (CONSTANT_MINSIGSTKSZ),
		  "CONSTANT_MINSIGSTKSZ is constant");
  GLRO(dl_minsigstacksize) = CONSTANT_MINSIGSTKSZ;

  for (av = GLRO(dl_auxv); av->a_type != AT_NULL; av++)
    switch (av->a_type)
      {
      case AT_PHDR:
	phdr = (void *) av->a_un.a_val;
	break;
      case AT_PHNUM:
	phnum = av->a_un.a_val;
	break;
      case AT_PAGESZ:
	GLRO(dl_pagesize) = av->a_un.a_val;
	break;
      case AT_ENTRY:
	user_entry = av->a_un.a_val;
	break;
      case AT_SECURE:
	__libc_enable_secure = av->a_un.a_val;
	break;
      case AT_PLATFORM:
	GLRO(dl_platform) = (void *) av->a_un.a_val;
	break;
      case AT_HWCAP:
	GLRO(dl_hwcap) = (unsigned long int) av->a_un.a_val;
	break;
      case AT_HWCAP2:
	GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
	break;
      case AT_CLKTCK:
	GLRO(dl_clktck) = av->a_un.a_val;
	break;
      case AT_FPUCW:
	GLRO(dl_fpu_control) = av->a_un.a_val;
	break;
#ifdef NEED_DL_SYSINFO
      case AT_SYSINFO:
	new_sysinfo = av->a_un.a_val;
	break;
#endif
      case AT_SYSINFO_EHDR:
	GLRO(dl_sysinfo_dso) = (void *) av->a_un.a_val;
	break;
      case AT_RANDOM:
	_dl_random = (void *) av->a_un.a_val;
	break;
      case AT_MINSIGSTKSZ:
	GLRO(dl_minsigstacksize) = av->a_un.a_val;
	break;
      DL_PLATFORM_AUXV
      }

  dl_hwcap_check ();

#ifdef NEED_DL_SYSINFO
  if (new_sysinfo != 0)
    {
      /* Only set the sysinfo value if we also have the vsyscall DSO.  */
      if (GLRO(dl_sysinfo_dso) != 0)
        GLRO(dl_sysinfo) = new_sysinfo;
    }
#endif

  __tunables_init (_environ);

  /* Initialize DSO sorting algorithm after tunables.  */
  _dl_sort_maps_init ();

  __brk (0);			/* Initialize the break.  */

#ifdef DL_PLATFORM_INIT
  DL_PLATFORM_INIT;
#endif

  /* Determine the length of the platform name.  */
  if (GLRO(dl_platform) != NULL)
    GLRO(dl_platformlen) = strlen (GLRO(dl_platform));

  if (__sbrk (0) == _end)
    /* The dynamic linker was run as a program, and so the initial break
       starts just after our bss, at &_end.  The malloc in dl-minimal.c
       will consume the rest of this page, so tell the kernel to move the
       break up that far.  When the user program examines its break, it
       will see this new value and not clobber our data.  */
    __sbrk (GLRO(dl_pagesize)
	    - ((_end - (char *) 0) & (GLRO(dl_pagesize) - 1)));

  /* If this is a SUID program we make sure that FDs 0, 1, and 2 are
     allocated.  If necessary we are doing it ourself.  If it is not
     possible we stop the program.  */
  if (__builtin_expect (__libc_enable_secure, 0))
    __libc_check_standard_fds ();

  (*dl_main) (phdr, phnum, &user_entry, GLRO(dl_auxv));
  return user_entry;
}

void
_dl_sysdep_start_cleanup (void)
{
}

void
_dl_show_auxv (void)
{
  char buf[64];
  ElfW(auxv_t) *av;

  /* Terminate string.  */
  buf[63] = '\0';

  /* The following code assumes that the AT_* values are encoded
     starting from 0 with AT_NULL, 1 for AT_IGNORE, and all other values
     close by (otherwise the array will be too large).  In case we have
     to support a platform where these requirements are not fulfilled
     some alternative implementation has to be used.  */
  for (av = GLRO(dl_auxv); av->a_type != AT_NULL; ++av)
    {
      static const struct
      {
	const char label[22];
	enum { unknown = 0, dec, hex, str, ignore } form : 8;
      } auxvars[] =
	{
	  [AT_EXECFD - 2] =		{ "EXECFD:            ", dec },
	  [AT_EXECFN - 2] =		{ "EXECFN:            ", str },
	  [AT_PHDR - 2] =		{ "PHDR:              0x", hex },
	  [AT_PHENT - 2] =		{ "PHENT:             ", dec },
	  [AT_PHNUM - 2] =		{ "PHNUM:             ", dec },
	  [AT_PAGESZ - 2] =		{ "PAGESZ:            ", dec },
	  [AT_BASE - 2] =		{ "BASE:              0x", hex },
	  [AT_FLAGS - 2] =		{ "FLAGS:             0x", hex },
	  [AT_ENTRY - 2] =		{ "ENTRY:             0x", hex },
	  [AT_NOTELF - 2] =		{ "NOTELF:            ", hex },
	  [AT_UID - 2] =		{ "UID:               ", dec },
	  [AT_EUID - 2] =		{ "EUID:              ", dec },
	  [AT_GID - 2] =		{ "GID:               ", dec },
	  [AT_EGID - 2] =		{ "EGID:              ", dec },
	  [AT_PLATFORM - 2] =		{ "PLATFORM:          ", str },
	  [AT_HWCAP - 2] =		{ "HWCAP:             ", hex },
	  [AT_CLKTCK - 2] =		{ "CLKTCK:            ", dec },
	  [AT_FPUCW - 2] =		{ "FPUCW:             ", hex },
	  [AT_DCACHEBSIZE - 2] =	{ "DCACHEBSIZE:       0x", hex },
	  [AT_ICACHEBSIZE - 2] =	{ "ICACHEBSIZE:       0x", hex },
	  [AT_UCACHEBSIZE - 2] =	{ "UCACHEBSIZE:       0x", hex },
	  [AT_IGNOREPPC - 2] =		{ "IGNOREPPC", ignore },
	  [AT_SECURE - 2] =		{ "SECURE:            ", dec },
	  [AT_BASE_PLATFORM - 2] =	{ "BASE_PLATFORM:     ", str },
	  [AT_SYSINFO - 2] =		{ "SYSINFO:           0x", hex },
	  [AT_SYSINFO_EHDR - 2] =	{ "SYSINFO_EHDR:      0x", hex },
	  [AT_RANDOM - 2] =		{ "RANDOM:            0x", hex },
	  [AT_HWCAP2 - 2] =		{ "HWCAP2:            0x", hex },
	  [AT_MINSIGSTKSZ - 2] =	{ "MINSIGSTKSZ:       ", dec },
	  [AT_L1I_CACHESIZE - 2] =	{ "L1I_CACHESIZE:     ", dec },
	  [AT_L1I_CACHEGEOMETRY - 2] =	{ "L1I_CACHEGEOMETRY: 0x", hex },
	  [AT_L1D_CACHESIZE - 2] =	{ "L1D_CACHESIZE:     ", dec },
	  [AT_L1D_CACHEGEOMETRY - 2] =	{ "L1D_CACHEGEOMETRY: 0x", hex },
	  [AT_L2_CACHESIZE - 2] =	{ "L2_CACHESIZE:      ", dec },
	  [AT_L2_CACHEGEOMETRY - 2] =	{ "L2_CACHEGEOMETRY:  0x", hex },
	  [AT_L3_CACHESIZE - 2] =	{ "L3_CACHESIZE:      ", dec },
	  [AT_L3_CACHEGEOMETRY - 2] =	{ "L3_CACHEGEOMETRY:  0x", hex },
	};
      unsigned int idx = (unsigned int) (av->a_type - 2);

      if ((unsigned int) av->a_type < 2u
	  || (idx < sizeof (auxvars) / sizeof (auxvars[0])
	      && auxvars[idx].form == ignore))
	continue;

      assert (AT_NULL == 0);
      assert (AT_IGNORE == 1);

      /* Some entries are handled in a special way per platform.  */
      if (_dl_procinfo (av->a_type, av->a_un.a_val) == 0)
	continue;

      if (idx < sizeof (auxvars) / sizeof (auxvars[0])
	  && auxvars[idx].form != unknown)
	{
	  const char *val = (char *) av->a_un.a_val;

	  if (__builtin_expect (auxvars[idx].form, dec) == dec)
	    val = _itoa ((unsigned long int) av->a_un.a_val,
			 buf + sizeof buf - 1, 10, 0);
	  else if (__builtin_expect (auxvars[idx].form, hex) == hex)
	    val = _itoa ((unsigned long int) av->a_un.a_val,
			 buf + sizeof buf - 1, 16, 0);

	  _dl_printf ("AT_%s%s\n", auxvars[idx].label, val);

	  continue;
	}

      /* Unknown value: print a generic line.  */
      char buf2[17];
      buf2[sizeof (buf2) - 1] = '\0';
      const char *val2 = _itoa ((unsigned long int) av->a_un.a_val,
				buf2 + sizeof buf2 - 1, 16, 0);
      const char *val =  _itoa ((unsigned long int) av->a_type,
				buf + sizeof buf - 1, 16, 0);
      _dl_printf ("AT_??? (0x%s): 0x%s\n", val, val2);
    }
}

#endif /* SHARED */


int
attribute_hidden
_dl_discover_osversion (void)
{
#ifdef SHARED
  if (GLRO(dl_sysinfo_map) != NULL)
    {
      /* If the kernel-supplied DSO contains a note indicating the kernel's
	 version, we don't need to call uname or parse any strings.  */

      static const struct
      {
	ElfW(Nhdr) hdr;
	char vendor[8];
      } expected_note = { { sizeof "Linux", sizeof (ElfW(Word)), 0 }, "Linux" };
      const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;
      const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;
      for (uint_fast16_t i = 0; i < phnum; ++i)
	if (phdr[i].p_type == PT_NOTE)
	  {
	    const ElfW(Addr) start = (phdr[i].p_vaddr
				      + GLRO(dl_sysinfo_map)->l_addr);
	    const ElfW(Nhdr) *note = (const void *) start;
	    while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
	      {
		if (!memcmp (note, &expected_note, sizeof expected_note))
		  return *(const ElfW(Word) *) ((const void *) note
						+ sizeof expected_note);
#define ROUND(len) (((len) + sizeof note->n_type - 1) & -sizeof note->n_type)
		note = ((const void *) (note + 1)
			+ ROUND (note->n_namesz) + ROUND (note->n_descsz));
#undef ROUND
	      }
	  }
    }
#endif /* SHARED */

  char bufmem[64];
  char *buf = bufmem;
  unsigned int version;
  int parts;
  char *cp;
  struct utsname uts;

  /* Try the uname system call.  */
  if (__uname (&uts))
    {
      /* This was not successful.  Now try reading the /proc filesystem.  */
      int fd = __open64_nocancel ("/proc/sys/kernel/osrelease", O_RDONLY);
      if (fd < 0)
	return -1;
      ssize_t reslen = __read_nocancel (fd, bufmem, sizeof (bufmem));
      __close_nocancel (fd);
      if (reslen <= 0)
	/* This also didn't work.  We give up since we cannot
	   make sure the library can actually work.  */
	return -1;
      buf[MIN (reslen, (ssize_t) sizeof (bufmem) - 1)] = '\0';
    }
  else
    buf = uts.release;

  /* Now convert it into a number.  The string consists of at most
     three parts.  */
  version = 0;
  parts = 0;
  cp = buf;
  while ((*cp >= '0') && (*cp <= '9'))
    {
      unsigned int here = *cp++ - '0';

      while ((*cp >= '0') && (*cp <= '9'))
	{
	  here *= 10;
	  here += *cp++ - '0';
	}

      ++parts;
      version <<= 8;
      version |= here;

      if (*cp++ != '.' || parts == 3)
	/* Another part following?  */
	break;
    }

  if (parts < 3)
    version <<= 8 * (3 - parts);

  return version;
}