From e85ec62d2bc38aba887ae6b94474bcc69aabd759 Mon Sep 17 00:00:00 2001
From: Ulrich Drepper <drepper@redhat.com>
Date: Tue, 15 Dec 2009 12:32:27 -0800
Subject: [PATCH 3/4] Avoid ELF lookup race.
On some architectures the update of the l_used field in the lookup
functions races with setting the other bits in the bitfield. Simply
avoid this and optimize use of l_used in general.
(adjusted cherry-pick from 2af6396817fb9df98e63de75dd59fd999ee9f1d0)
---
ChangeLog | 8 ++++++++
elf/dl-lookup.c | 7 ++++---
elf/dl-object.c | 8 ++++++--
include/link.h | 8 +++++---
4 files changed, 23 insertions(+), 8 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 96bc0e7..12dc32a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2009-12-15 Ulrich Drepper <drepper@redhat.com>
+
+ * include/link.h (struct link_map): Move l_used into its own word.
+ * elf/dl-lookup.c (_dl_lookup_symbol_x): Only update l_used when it is
+ still zero.
+ * elf/dl-object.c (_dl_new_object): Set dl_used if we know it is
+ never really used.
+
2009-12-11 Ulrich Drepper <drepper@redhat.com>
* sysdeps/unix/sysv/linux/sh/bits/fcntl.h: Redefine O_SYNC and
diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c
index c1a1366..763ec16 100644
--- a/elf/dl-lookup.c
+++ b/elf/dl-lookup.c
@@ -777,7 +777,7 @@ _dl_lookup_symbol_x (const char *undef_name, struct link_map *undef_map,
if (__builtin_expect (protected != 0, 0))
{
/* It is very tricky. We need to figure out what value to
- return for the protected symbol. */
+ return for the protected symbol. */
if (type_class == ELF_RTYPE_CLASS_PLT)
{
if (current_value.s != NULL && current_value.m != undef_map)
@@ -822,7 +822,8 @@ _dl_lookup_symbol_x (const char *undef_name, struct link_map *undef_map,
version, type_class, flags, skip_map);
/* The object is used. */
- current_value.m->l_used = 1;
+ if (__builtin_expect (current_value.m->l_used == 0, 0))
+ current_value.m->l_used = 1;
if (__builtin_expect (GLRO(dl_debug_mask)
& (DL_DEBUG_BINDINGS|DL_DEBUG_PRELINK), 0))
@@ -844,7 +845,7 @@ _dl_setup_hash (struct link_map *map)
Elf_Symndx nchain;
if (__builtin_expect (map->l_info[DT_ADDRTAGIDX (DT_GNU_HASH) + DT_NUM
- + DT_THISPROCNUM + DT_VERSIONTAGNUM
+ + DT_THISPROCNUM + DT_VERSIONTAGNUM
+ DT_EXTRANUM + DT_VALNUM] != NULL, 1))
{
Elf32_Word *hash32
diff --git a/elf/dl-object.c b/elf/dl-object.c
index be4ea38..788e2c0 100644
--- a/elf/dl-object.c
+++ b/elf/dl-object.c
@@ -1,5 +1,5 @@
/* Storage management for the chain of loaded shared objects.
- Copyright (C) 1995-2002,2004,2006,2007,2008 Free Software Foundation, Inc.
+ Copyright (C) 1995-2002,2004,2006-2008,2009 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
@@ -67,6 +67,10 @@ _dl_new_object (char *realname, const char *libname, int type,
new->l_name = realname;
new->l_type = type;
+ /* If we set the bit now since we know it is never used we avoid
+ dirtying the cache line later. */
+ if ((GLRO(dl_debug_mask) & DL_DEBUG_UNUSED) == 0)
+ new->l_used = 1;
new->l_loader = loader;
#if NO_TLS_OFFSET != 0
new->l_tls_offset = NO_TLS_OFFSET;
@@ -174,7 +178,7 @@ _dl_new_object (char *realname, const char *libname, int type,
if (result == NULL)
{
/* We were not able to determine the current directory.
- Note that free(origin) is OK if origin == NULL. */
+ Note that free(origin) is OK if origin == NULL. */
free (origin);
origin = (char *) -1;
goto out;
diff --git a/include/link.h b/include/link.h
index 4b9978a..26c6743 100644
--- a/include/link.h
+++ b/include/link.h
@@ -1,6 +1,6 @@
/* Data structure for communication from the run-time dynamic linker for
loaded ELF shared objects.
- Copyright (C) 1995-2006, 2007 Free Software Foundation, Inc.
+ Copyright (C) 1995-2006, 2007, 2009 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
@@ -180,7 +180,6 @@ struct link_map
unsigned int l_need_tls_init:1; /* Nonzero if GL(dl_init_static_tls)
should be called on this link map
when relocation finishes. */
- unsigned int l_used:1; /* Nonzero if the DSO is used. */
unsigned int l_auditing:1; /* Nonzero if the DSO is used in auditing. */
unsigned int l_audit_any_plt:1; /* Nonzero if at least one audit module
is interested in the PLT interception.*/
@@ -239,12 +238,15 @@ struct link_map
struct link_map **l_initfini;
/* List of the dependencies introduced through symbol binding. */
- unsigned int l_reldepsmax;
struct link_map_reldeps
{
unsigned int act;
struct link_map *list[];
} *l_reldeps;
+ unsigned int l_reldepsmax;
+
+ /* Nonzero if the DSO is used. */
+ unsigned int l_used;
/* Various flag words. */
ElfW(Word) l_feature_1;
--
1.7.0
