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* [glibc] elf: Remove ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA
@ 2022-06-15 18:29 Fangrui Song
0 siblings, 0 replies; only message in thread
From: Fangrui Song @ 2022-06-15 18:29 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=de38b2a343e6d64b95c50004943d6107a9e380d0
commit de38b2a343e6d64b95c50004943d6107a9e380d0
Author: Fangrui Song <maskray@google.com>
Date: Wed Jun 15 11:29:55 2022 -0700
elf: Remove ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA
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 62da1e3b00b51383ffa7efc89d8addda0502e107 (x86) and then
copied to nios2 (ae5eae7cfc9c4a8297ff82ec6b794faca1976ecc) and arc
(0e7d930c4c11de896fe807f67fa1eb756c9c1e05).
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 7374c02b683b7110b853a32496a619410364d70b. 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.
Diff:
---
elf/dl-lookup.c | 60 +--------------------------------------------
sysdeps/arc/dl-sysdep.h | 21 ----------------
sysdeps/generic/ldsodefs.h | 12 +--------
sysdeps/i386/dl-machine.h | 3 +--
sysdeps/nios2/dl-sysdep.h | 21 ----------------
sysdeps/x86/dl-lookupcfg.h | 4 ---
sysdeps/x86_64/dl-machine.h | 8 ++----
7 files changed, 5 insertions(+), 124 deletions(-)
diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c
index a42f6d5390..8cb32321da 100644
--- a/elf/dl-lookup.c
+++ b/elf/dl-lookup.c
@@ -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)
diff --git a/sysdeps/arc/dl-sysdep.h b/sysdeps/arc/dl-sysdep.h
deleted file mode 100644
index cf4d160a73..0000000000
--- a/sysdeps/arc/dl-sysdep.h
+++ /dev/null
@@ -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
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 446d12a68c..050a3032de 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -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,
diff --git a/sysdeps/i386/dl-machine.h b/sysdeps/i386/dl-machine.h
index 8779983c8c..a8ee594ff4 100644
--- a/sysdeps/i386/dl-machine.h
+++ b/sysdeps/i386/dl-machine.h
@@ -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
diff --git a/sysdeps/nios2/dl-sysdep.h b/sysdeps/nios2/dl-sysdep.h
deleted file mode 100644
index 257b37c258..0000000000
--- a/sysdeps/nios2/dl-sysdep.h
+++ /dev/null
@@ -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
diff --git a/sysdeps/x86/dl-lookupcfg.h b/sysdeps/x86/dl-lookupcfg.h
index 18b3b49f6e..e136cc63af 100644
--- a/sysdeps/x86/dl-lookupcfg.h
+++ b/sysdeps/x86/dl-lookupcfg.h
@@ -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;
diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
index b9122944b9..06c9a932b0 100644
--- a/sysdeps/x86_64/dl-machine.h
+++ b/sysdeps/x86_64/dl-machine.h
@@ -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
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