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elf: Remove ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA

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If an executable has copy relocations for extern protected data, that
can only work if the library containing the definition is built with
assumptions (a) the compiler emits GOT-generating relocations (b) the
linker produces R_*_GLOB_DAT instead of R_*_RELATIVE.  Otherwise the
library uses its own definition directly and the executable accesses a
stale copy.  Note: the GOT relocations defeat the purpose of protected
visibility as an optimization, but allow rtld to make the executable and
library use the same copy when copy relocations are present, but it
turns out this never worked perfectly.

ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA has strange semantics when both
a.so and b.so define protected var and the executable copy relocates
var: b.so accesses its own copy even with GLOB_DAT.  The behavior change
is from commit 62da1e3b00 (x86) and then
copied to nios2 (ae5eae7cfc) and arc
(0e7d930c4c).

Without ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA, b.so accesses the copy
relocated data like a.so.

There is now a warning for copy relocation on protected symbol since
commit 7374c02b68.  It's extremely
unlikely anyone relies on the ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA
behavior, so let's remove it: this removes a check in the symbol lookup
code.
This commit is contained in:
Fangrui Song 2022-06-15 11:29:55 -07:00
parent ff439c4717
commit de38b2a343
7 changed files with 5 additions and 124 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

60
elf/dl-lookup.c
View File

@ -456,59 +456,6 @@ do_lookup_x (const char *undef_name, unsigned int new_hash,
if (sym != NULL)
{
found_it:
/* When UNDEF_MAP is NULL, which indicates we are called from
do_lookup_x on relocation against protected data, we skip
the data definion in the executable from copy reloc. */
if (ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA
&& undef_map == NULL
&& map->l_type == lt_executable
&& type_class == ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA)
{
const ElfW(Sym) *s;
unsigned int i;
#if ! ELF_MACHINE_NO_RELA
if (map->l_info[DT_RELA] != NULL
&& map->l_info[DT_RELASZ] != NULL
&& map->l_info[DT_RELASZ]->d_un.d_val != 0)
{
const ElfW(Rela) *rela
= (const ElfW(Rela) *) D_PTR (map, l_info[DT_RELA]);
unsigned int rela_count
= map->l_info[DT_RELASZ]->d_un.d_val / sizeof (*rela);
for (i = 0; i < rela_count; i++, rela++)
if (elf_machine_type_class (ELFW(R_TYPE) (rela->r_info))
== ELF_RTYPE_CLASS_COPY)
{
s = &symtab[ELFW(R_SYM) (rela->r_info)];
if (!strcmp (strtab + s->st_name, undef_name))
goto skip;
}
}
#endif
#if ! ELF_MACHINE_NO_REL
if (map->l_info[DT_REL] != NULL
&& map->l_info[DT_RELSZ] != NULL
&& map->l_info[DT_RELSZ]->d_un.d_val != 0)
{
const ElfW(Rel) *rel
= (const ElfW(Rel) *) D_PTR (map, l_info[DT_REL]);
unsigned int rel_count
= map->l_info[DT_RELSZ]->d_un.d_val / sizeof (*rel);
for (i = 0; i < rel_count; i++, rel++)
if (elf_machine_type_class (ELFW(R_TYPE) (rel->r_info))
== ELF_RTYPE_CLASS_COPY)
{
s = &symtab[ELFW(R_SYM) (rel->r_info)];
if (!strcmp (strtab + s->st_name, undef_name))
goto skip;
}
}
#endif
}
/* Hidden and internal symbols are local, ignore them. */
if (__glibc_unlikely (dl_symbol_visibility_binds_local_p (sym)))
goto skip;
@ -875,12 +822,7 @@ _dl_lookup_symbol_x (const char *undef_name, struct link_map *undef_map,
for (scope = symbol_scope; *scope != NULL; i = 0, ++scope)
if (do_lookup_x (undef_name, new_hash, &old_hash, *ref,
&protected_value, *scope, i, version, flags,
skip_map,
(ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA
&& ELFW(ST_TYPE) ((*ref)->st_info) == STT_OBJECT
&& type_class == ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA)
? ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA
: ELF_RTYPE_CLASS_PLT, NULL) != 0)
skip_map, ELF_RTYPE_CLASS_PLT, NULL) != 0)
break;
if (protected_value.s != NULL && protected_value.m != undef_map)

21
sysdeps/arc/dl-sysdep.h
View File

@ -1,21 +0,0 @@
/* System-specific settings for dynamic linker code. ARC version.
Copyright (C) 2020-2022 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_next <dl-sysdep.h>
#define DL_EXTERN_PROTECTED_DATA

12
sysdeps/generic/ldsodefs.h
View File

@ -149,23 +149,13 @@ dl_symbol_visibility_binds_local_p (const ElfW(Sym) *sym)
satisfied by any symbol in the executable. Some architectures do
not support copy relocations. In this case we define the macro to
zero so that the code for handling them gets automatically optimized
out. ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA means address of protected
data defined in the shared library may be external, i.e., due to copy
relocation. */
out. */
#define ELF_RTYPE_CLASS_PLT 1
#ifndef DL_NO_COPY_RELOCS
# define ELF_RTYPE_CLASS_COPY 2
#else
# define ELF_RTYPE_CLASS_COPY 0
#endif
/* If DL_EXTERN_PROTECTED_DATA is defined, address of protected data
defined in the shared library may be external, i.e., due to copy
relocation. */
#ifdef DL_EXTERN_PROTECTED_DATA
# define ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA 4
#else
# define ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA 0
#endif
/* ELF uses the PF_x macros to specify the segment permissions, mmap
uses PROT_xxx. In most cases the three macros have the values 1, 2,

3
sysdeps/i386/dl-machine.h
View File

@ -194,8 +194,7 @@ _dl_start_user:\n\
|| (type) == R_386_TLS_DTPOFF32 || (type) == R_386_TLS_TPOFF32 \
|| (type) == R_386_TLS_TPOFF || (type) == R_386_TLS_DESC) \
* ELF_RTYPE_CLASS_PLT) \
| (((type) == R_386_COPY) * ELF_RTYPE_CLASS_COPY) \
| (((type) == R_386_GLOB_DAT) * ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA))
| (((type) == R_386_COPY) * ELF_RTYPE_CLASS_COPY))
/* A reloc type used for ld.so cmdline arg lookups to reject PLT entries. */
#define ELF_MACHINE_JMP_SLOT R_386_JMP_SLOT

21
sysdeps/nios2/dl-sysdep.h
View File

@ -1,21 +0,0 @@
/* System-specific settings for dynamic linker code. Nios II version.
Copyright (C) 2009-2022 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_next <dl-sysdep.h>
#define DL_EXTERN_PROTECTED_DATA

4
sysdeps/x86/dl-lookupcfg.h
View File

@ -20,10 +20,6 @@
#include_next <dl-lookupcfg.h>
/* Address of protected data defined in the shared library may be
external due to copy relocation. */
#define DL_EXTERN_PROTECTED_DATA
struct link_map;
extern void _dl_unmap (struct link_map *map) attribute_hidden;

8
sysdeps/x86_64/dl-machine.h
View File

@ -172,10 +172,7 @@ _dl_start_user:\n\
TLS variable, so undefined references should not be allowed to
define the value.
ELF_RTYPE_CLASS_COPY iff TYPE should not be allowed to resolve to one
of the main executable's symbols, as for a COPY reloc.
ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA iff TYPE describes relocation may
against protected data whose address be external due to copy relocation.
*/
of the main executable's symbols, as for a COPY reloc. */
#define elf_machine_type_class(type) \
((((type) == R_X86_64_JUMP_SLOT \
|| (type) == R_X86_64_DTPMOD64 \
@ -183,8 +180,7 @@ _dl_start_user:\n\
|| (type) == R_X86_64_TPOFF64 \
|| (type) == R_X86_64_TLSDESC) \
* ELF_RTYPE_CLASS_PLT) \
| (((type) == R_X86_64_COPY) * ELF_RTYPE_CLASS_COPY) \
| (((type) == R_X86_64_GLOB_DAT) * ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA))
| (((type) == R_X86_64_COPY) * ELF_RTYPE_CLASS_COPY))
/* A reloc type used for ld.so cmdline arg lookups to reject PLT entries. */
#define ELF_MACHINE_JMP_SLOT R_X86_64_JUMP_SLOT