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glibc/elf/get-dynamic-info.h
Florian Weimer f8ed116aa5 dlopen: Rework handling of pending NODELETE status 
Commit a2e8aa0d9e ("Block signals during
the initial part of dlopen") was deemed necessary because of
read-modify-write operations like the one in  add_dependency in
elf/dl-lookup.c.  In the old code, we check for any kind of NODELETE
status and bail out:

      /* Redo the NODELETE check, as when dl_load_lock wasn't held
	 yet this could have changed.  */
      if (map->l_nodelete != link_map_nodelete_inactive)
	goto out;

And then set pending status (during relocation):

	  if (flags & DL_LOOKUP_FOR_RELOCATE)
	    map->l_nodelete = link_map_nodelete_pending;
	  else
	    map->l_nodelete = link_map_nodelete_active;

If a signal arrives during relocation and the signal handler, through
lazy binding, adds a global scope dependency on the same map, it will
set map->l_nodelete to link_map_nodelete_active.  This will be
overwritten with link_map_nodelete_pending by the dlopen relocation
code.

To avoid such problems in relation to the l_nodelete member, this
commit introduces two flags for active NODELETE status (irrevocable)
and pending NODELETE status (revocable until activate_nodelete is
invoked).  As a result, NODELETE processing in dlopen does not
introduce further reasons why lazy binding from signal handlers
is unsafe during dlopen, and a subsequent commit can remove signal
blocking from dlopen.

This does not address pre-existing issues (unrelated to the NODELETE
changes) which make lazy binding in a signal handler during dlopen
unsafe, such as the use of malloc in both cases.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
2019-12-13 10:18:46 +01:00

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/* Read the dynamic section at DYN and fill in INFO with indices DT_*.
Copyright (C) 2012-2019 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 is included multiple times and therefore lacks a header
file inclusion guard. */
#include <assert.h>
#include <libc-diag.h>
#ifndef RESOLVE_MAP
static
#else
auto
#endif
inline void __attribute__ ((unused, always_inline))
elf_get_dynamic_info (struct link_map *l, ElfW(Dyn) *temp)
{
ElfW(Dyn) *dyn = l->l_ld;
ElfW(Dyn) **info;
#if __ELF_NATIVE_CLASS == 32
typedef Elf32_Word d_tag_utype;
#elif __ELF_NATIVE_CLASS == 64
typedef Elf64_Xword d_tag_utype;
#endif
#if !defined RTLD_BOOTSTRAP && !defined STATIC_PIE_BOOTSTRAP
if (dyn == NULL)
return;
#endif
info = l->l_info;
while (dyn->d_tag != DT_NULL)
{
if ((d_tag_utype) dyn->d_tag < DT_NUM)
info[dyn->d_tag] = dyn;
else if (dyn->d_tag >= DT_LOPROC
&& dyn->d_tag < DT_LOPROC + DT_THISPROCNUM)
{
/* This does not violate the array bounds of l->l_info, but
gcc 4.6 on sparc somehow does not see this. */
DIAG_PUSH_NEEDS_COMMENT;
DIAG_IGNORE_NEEDS_COMMENT (4.6,
"-Warray-bounds");
info[dyn->d_tag - DT_LOPROC + DT_NUM] = dyn;
DIAG_POP_NEEDS_COMMENT;
}
else if ((d_tag_utype) DT_VERSIONTAGIDX (dyn->d_tag) < DT_VERSIONTAGNUM)
info[VERSYMIDX (dyn->d_tag)] = dyn;
else if ((d_tag_utype) DT_EXTRATAGIDX (dyn->d_tag) < DT_EXTRANUM)
info[DT_EXTRATAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM
+ DT_VERSIONTAGNUM] = dyn;
else if ((d_tag_utype) DT_VALTAGIDX (dyn->d_tag) < DT_VALNUM)
info[DT_VALTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM
+ DT_VERSIONTAGNUM + DT_EXTRANUM] = dyn;
else if ((d_tag_utype) DT_ADDRTAGIDX (dyn->d_tag) < DT_ADDRNUM)
info[DT_ADDRTAGIDX (dyn->d_tag) + DT_NUM + DT_THISPROCNUM
+ DT_VERSIONTAGNUM + DT_EXTRANUM + DT_VALNUM] = dyn;
++dyn;
}
#define DL_RO_DYN_TEMP_CNT 8
#ifndef DL_RO_DYN_SECTION
/* Don't adjust .dynamic unnecessarily. */
if (l->l_addr != 0)
{
ElfW(Addr) l_addr = l->l_addr;
int cnt = 0;
# define ADJUST_DYN_INFO(tag) \
do \
if (info[tag] != NULL) \
{ \
if (temp) \
{ \
temp[cnt].d_tag = info[tag]->d_tag; \
temp[cnt].d_un.d_ptr = info[tag]->d_un.d_ptr + l_addr; \
info[tag] = temp + cnt++; \
} \
else \
info[tag]->d_un.d_ptr += l_addr; \
} \
while (0)
ADJUST_DYN_INFO (DT_HASH);
ADJUST_DYN_INFO (DT_PLTGOT);
ADJUST_DYN_INFO (DT_STRTAB);
ADJUST_DYN_INFO (DT_SYMTAB);
# if ! ELF_MACHINE_NO_RELA
ADJUST_DYN_INFO (DT_RELA);
# endif
# if ! ELF_MACHINE_NO_REL
ADJUST_DYN_INFO (DT_REL);
# endif
ADJUST_DYN_INFO (DT_JMPREL);
ADJUST_DYN_INFO (VERSYMIDX (DT_VERSYM));
ADJUST_DYN_INFO (ADDRIDX (DT_GNU_HASH));
# undef ADJUST_DYN_INFO
assert (cnt <= DL_RO_DYN_TEMP_CNT);
}
#endif
if (info[DT_PLTREL] != NULL)
{
#if ELF_MACHINE_NO_RELA
assert (info[DT_PLTREL]->d_un.d_val == DT_REL);
#elif ELF_MACHINE_NO_REL
assert (info[DT_PLTREL]->d_un.d_val == DT_RELA);
#else
assert (info[DT_PLTREL]->d_un.d_val == DT_REL
|| info[DT_PLTREL]->d_un.d_val == DT_RELA);
#endif
}
#if ! ELF_MACHINE_NO_RELA
if (info[DT_RELA] != NULL)
assert (info[DT_RELAENT]->d_un.d_val == sizeof (ElfW(Rela)));
# endif
# if ! ELF_MACHINE_NO_REL
if (info[DT_REL] != NULL)
assert (info[DT_RELENT]->d_un.d_val == sizeof (ElfW(Rel)));
#endif
#ifdef RTLD_BOOTSTRAP
/* Only the bind now flags are allowed. */
assert (info[VERSYMIDX (DT_FLAGS_1)] == NULL
|| (info[VERSYMIDX (DT_FLAGS_1)]->d_un.d_val & ~DF_1_NOW) == 0);
/* Flags must not be set for ld.so. */
assert (info[DT_FLAGS] == NULL
|| (info[DT_FLAGS]->d_un.d_val & ~DF_BIND_NOW) == 0);
#endif
#if defined RTLD_BOOTSTRAP || defined STATIC_PIE_BOOTSTRAP
assert (info[DT_RUNPATH] == NULL);
assert (info[DT_RPATH] == NULL);
#else
if (info[DT_FLAGS] != NULL)
{
/* Flags are used. Translate to the old form where available.
Since these l_info entries are only tested for NULL pointers it
is ok if they point to the DT_FLAGS entry. */
l->l_flags = info[DT_FLAGS]->d_un.d_val;
if (l->l_flags & DF_SYMBOLIC)
info[DT_SYMBOLIC] = info[DT_FLAGS];
if (l->l_flags & DF_TEXTREL)
info[DT_TEXTREL] = info[DT_FLAGS];
if (l->l_flags & DF_BIND_NOW)
info[DT_BIND_NOW] = info[DT_FLAGS];
}
if (info[VERSYMIDX (DT_FLAGS_1)] != NULL)
{
l->l_flags_1 = info[VERSYMIDX (DT_FLAGS_1)]->d_un.d_val;
if (l->l_flags_1 & DF_1_NODELETE)
l->l_nodelete_pending = true;
/* Only DT_1_SUPPORTED_MASK bits are supported, and we would like
to assert this, but we can't. Users have been setting
unsupported DF_1_* flags for a long time and glibc has ignored
them. Therefore to avoid breaking existing applications the
best we can do is add a warning during debugging with the
intent of notifying the user of the problem. */
if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_FILES, 0)
&& l->l_flags_1 & ~DT_1_SUPPORTED_MASK)
_dl_debug_printf ("\nWARNING: Unsupported flag value(s) of 0x%x in DT_FLAGS_1.\n",
l->l_flags_1 & ~DT_1_SUPPORTED_MASK);
if (l->l_flags_1 & DF_1_NOW)
info[DT_BIND_NOW] = info[VERSYMIDX (DT_FLAGS_1)];
}
if (info[DT_RUNPATH] != NULL)
/* If both RUNPATH and RPATH are given, the latter is ignored. */
info[DT_RPATH] = NULL;
#endif
}
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