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authorFlorian Weimer <fweimer@redhat.com>2020-12-16 15:09:52 +0100
committerFlorian Weimer <fweimer@redhat.com>2020-12-16 15:13:40 +0100
commite7570f4131a6af9405af7b4fd1c31de807e7cf68 (patch)
tree0f11050a7a1b768fb0d683dc60412bc2a101c3a5
parent9459fe9da0f981f77ba931790f82e43ac552b73c (diff)
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Replace __libc_multiple_libcs with __libc_initial flag
Change sbrk to fail for !__libc_initial (in the generic implementation). As a result, sbrk is (relatively) safe to use for the __libc_initial case (from the main libc). It is therefore no longer necessary to avoid using it in that case (or updating the brk cache), and the __libc_initial flag does not need to be updated as part of dlmopen or static dlopen. As before, direct brk system calls on Linux may lead to memory corruption. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
-rw-r--r--csu/init-first.c10
-rw-r--r--csu/libc-start.c13
-rw-r--r--elf/dl-open.c6
-rw-r--r--elf/dl-sysdep.c2
-rw-r--r--elf/libc_early_init.c9
-rw-r--r--include/libc-internal.h7
-rw-r--r--misc/sbrk.c34
-rw-r--r--sysdeps/mach/hurd/dl-sysdep.c2
-rw-r--r--sysdeps/mach/hurd/i386/init-first.c10
9 files changed, 53 insertions, 40 deletions
diff --git a/csu/init-first.c b/csu/init-first.c
index 47aaacd..2115215 100644
--- a/csu/init-first.c
+++ b/csu/init-first.c
@@ -28,10 +28,6 @@
#include <ldsodefs.h>
-/* Set nonzero if we have to be prepared for more than one libc being
- used in the process. Safe assumption if initializer never runs. */
-int __libc_multiple_libcs attribute_hidden = 1;
-
/* Remember the command line argument and enviroment contents for
later calls of initializers for dynamic libraries. */
int __libc_argc attribute_hidden;
@@ -50,16 +46,16 @@ _init_first (int argc, char **argv, char **envp)
{
#endif
- __libc_multiple_libcs = &_dl_starting_up && !_dl_starting_up;
-
/* Make sure we don't initialize twice. */
- if (!__libc_multiple_libcs)
+#ifdef SHARED
+ if (__libc_initial)
{
/* Set the FPU control word to the proper default value if the
kernel would use a different value. */
if (__fpu_control != GLRO(dl_fpu_control))
__setfpucw (__fpu_control);
}
+#endif
/* Save the command-line arguments. */
__libc_argc = argc;
diff --git a/csu/libc-start.c b/csu/libc-start.c
index 2d4d2ed..d330812 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -141,8 +141,6 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
/* Result of the 'main' function. */
int result;
- __libc_multiple_libcs = &_dl_starting_up && !_dl_starting_up;
-
#ifndef SHARED
_dl_relocate_static_pie ();
@@ -213,12 +211,11 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
# endif
# ifdef DL_SYSDEP_OSCHECK
- if (!__libc_multiple_libcs)
- {
- /* This needs to run to initiliaze _dl_osversion before TLS
- setup might check it. */
- DL_SYSDEP_OSCHECK (__libc_fatal);
- }
+ {
+ /* This needs to run to initiliaze _dl_osversion before TLS
+ setup might check it. */
+ DL_SYSDEP_OSCHECK (__libc_fatal);
+ }
# endif
/* Initialize libpthread if linked in. */
diff --git a/elf/dl-open.c b/elf/dl-open.c
index 8769e47..6710ea0 100644
--- a/elf/dl-open.c
+++ b/elf/dl-open.c
@@ -787,12 +787,6 @@ dl_open_worker (void *a)
if (mode & RTLD_GLOBAL)
add_to_global_update (new);
-#ifndef SHARED
- /* We must be the static _dl_open in libc.a. A static program that
- has loaded a dynamic object now has competition. */
- __libc_multiple_libcs = 1;
-#endif
-
/* Let the user know about the opencount. */
if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES))
_dl_debug_printf ("opening file=%s [%lu]; direct_opencount=%u\n\n",
diff --git a/elf/dl-sysdep.c b/elf/dl-sysdep.c
index 8545708..6cc4a76 100644
--- a/elf/dl-sysdep.c
+++ b/elf/dl-sysdep.c
@@ -58,8 +58,6 @@ ElfW(Addr) _dl_base_addr;
#endif
int __libc_enable_secure attribute_relro = 0;
rtld_hidden_data_def (__libc_enable_secure)
-int __libc_multiple_libcs = 0; /* Defining this here avoids the inclusion
- of init-first. */
/* This variable contains the lowest stack address ever used. */
void *__libc_stack_end attribute_relro = NULL;
rtld_hidden_data_def(__libc_stack_end)
diff --git a/elf/libc_early_init.c b/elf/libc_early_init.c
index 725ab2f..28c6adc 100644
--- a/elf/libc_early_init.c
+++ b/elf/libc_early_init.c
@@ -18,8 +18,13 @@
#include <ctype.h>
#include <libc-early-init.h>
+#include <libc-internal.h>
#include <sys/single_threaded.h>
+#ifdef SHARED
+_Bool __libc_initial;
+#endif
+
void
__libc_early_init (_Bool initial)
{
@@ -28,4 +33,8 @@ __libc_early_init (_Bool initial)
/* Only the outer namespace is marked as single-threaded. */
__libc_single_threaded = initial;
+
+#ifdef SHARED
+ __libc_initial = initial;
+#endif
}
diff --git a/include/libc-internal.h b/include/libc-internal.h
index 915613c..c1e7405 100644
--- a/include/libc-internal.h
+++ b/include/libc-internal.h
@@ -47,6 +47,11 @@ extern void __init_misc (int, char **, char **) attribute_hidden;
extern __typeof (__profile_frequency) __profile_frequency attribute_hidden;
# endif
-extern int __libc_multiple_libcs attribute_hidden;
+#ifdef SHARED
+/* True if this libc belongs to the initially loaded program (i.e., it
+ is not for an audit module, not loaded via dlmopen, and not loaded
+ via static dlopen either). */
+extern _Bool __libc_initial attribute_hidden;
+#endif
#endif /* _LIBC_INTERNAL */
diff --git a/misc/sbrk.c b/misc/sbrk.c
index ba3322f..a6929d7 100644
--- a/misc/sbrk.c
+++ b/misc/sbrk.c
@@ -16,9 +16,10 @@
<https://www.gnu.org/licenses/>. */
#include <errno.h>
+#include <libc-internal.h>
+#include <stdbool.h>
#include <stdint.h>
#include <unistd.h>
-#include <libc-internal.h>
/* Defined in brk.c. */
extern void *__curbrk;
@@ -30,21 +31,34 @@ extern int __brk (void *addr);
void *
__sbrk (intptr_t increment)
{
- void *oldbrk;
-
- /* If this is not part of the dynamic library or the library is used
- via dynamic loading in a statically linked program update
- __curbrk from the kernel's brk value. That way two separate
- instances of __brk and __sbrk can share the heap, returning
- interleaved pieces of it. */
- if (__curbrk == NULL || __libc_multiple_libcs)
+ /* Controls whether __brk (0) is called to read the brk value from
+ the kernel. */
+ bool update_brk = __curbrk == NULL;
+
+#if defined (SHARED) && ! IS_IN (rtld)
+ if (!__libc_initial)
+ {
+ if (increment != 0)
+ {
+ /* Do not allow changing the brk from an inner libc because
+ it cannot be synchronized with the outer libc's brk. */
+ __set_errno (ENOMEM);
+ return (void *) -1;
+ }
+ /* Querying the kernel's brk value from an inner namespace is
+ fine. */
+ update_brk = true;
+ }
+#endif
+
+ if (update_brk)
if (__brk (0) < 0) /* Initialize the break. */
return (void *) -1;
if (increment == 0)
return __curbrk;
- oldbrk = __curbrk;
+ void *oldbrk = __curbrk;
if (increment > 0
? ((uintptr_t) oldbrk + (uintptr_t) increment < (uintptr_t) oldbrk)
: ((uintptr_t) oldbrk < (uintptr_t) -increment))
diff --git a/sysdeps/mach/hurd/dl-sysdep.c b/sysdeps/mach/hurd/dl-sysdep.c
index 3704957..a5169d8 100644
--- a/sysdeps/mach/hurd/dl-sysdep.c
+++ b/sysdeps/mach/hurd/dl-sysdep.c
@@ -57,8 +57,6 @@ extern char **_environ;
int __libc_enable_secure = 0;
rtld_hidden_data_def (__libc_enable_secure)
-int __libc_multiple_libcs = 0; /* Defining this here avoids the inclusion
- of init-first. */
/* This variable contains the lowest stack address ever used. */
void *__libc_stack_end = NULL;
rtld_hidden_data_def(__libc_stack_end)
diff --git a/sysdeps/mach/hurd/i386/init-first.c b/sysdeps/mach/hurd/i386/init-first.c
index 1827479..cbbc122 100644
--- a/sysdeps/mach/hurd/i386/init-first.c
+++ b/sysdeps/mach/hurd/i386/init-first.c
@@ -30,6 +30,7 @@
#include <ldsodefs.h>
#include <fpu_control.h>
#include <libc-diag.h>
+#include <libc-internal.h>
extern void __mach_init (void);
extern void __init_misc (int, char **, char **);
@@ -40,7 +41,6 @@ unsigned long int __hurd_threadvar_stack_mask;
#ifndef SHARED
int __libc_enable_secure;
#endif
-int __libc_multiple_libcs attribute_hidden = 1;
extern int __libc_argc attribute_hidden;
extern char **__libc_argv attribute_hidden;
@@ -56,13 +56,12 @@ DEFINE_HOOK (_hurd_preinit_hook, (void));
static void
posixland_init (int argc, char **argv, char **envp)
{
- __libc_multiple_libcs = &_dl_starting_up && !_dl_starting_up;
-
/* Now we have relocations etc. we can start signals etc. */
_hurd_libc_proc_init (argv);
+#ifdef SHARED
/* Make sure we don't initialize twice. */
- if (!__libc_multiple_libcs)
+ if (__libc_initial)
{
/* Set the FPU control word to the proper default value. */
__setfpucw (__fpu_control);
@@ -72,6 +71,9 @@ posixland_init (int argc, char **argv, char **envp)
/* Initialize data structures so the additional libc can do RPCs. */
__mach_init ();
}
+#else /* !SHARED */
+ __setfpucw (__fpu_control);
+#endif
/* Save the command-line arguments. */
__libc_argc = argc;