[PATCH] elf: Remove __libc_init_secure

[PATCH] elf: Remove __libc_init_secure

[Fangrui Song]

After 73fc4e28b9464f0e13edc719a5372839970e7ddb,
__libc_enable_secure_decided is always 0 and a statically linked
executable may overwrite __libc_enable_secure with a value not
considering AT_SECURE.

The __libc_enable_secure has been correctly initialized in _dl_aux_init,
so just remove __libc_enable_secure_decided and __libc_init_secure.
This allows us to remove some linux/i386 functions from
22b79ed7f413cd980a7af0cf258da5bf82b6d5e5.
---
 csu/libc-start.c                       |  3 ---
 elf/enbl-secure.c                      | 10 ---------
 include/libc-internal.h                |  3 ---
 include/unistd.h                       |  1 -
 sysdeps/mach/hurd/enbl-secure.c        | 30 --------------------------
 sysdeps/unix/sysv/linux/i386/startup.h | 24 ---------------------
 6 files changed, 71 deletions(-)
 delete mode 100644 sysdeps/mach/hurd/enbl-secure.c

diff --git a/csu/libc-start.c b/csu/libc-start.c
index e91f996426..b34bb6dbbc 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -285,9 +285,6 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
         }
     }
 
-  /* Initialize very early so that tunables can use it.  */
-  __libc_init_secure ();
-
   __tunables_init (__environ);
 
   ARCH_INIT_CPU_FEATURES ();
diff --git a/elf/enbl-secure.c b/elf/enbl-secure.c
index aa2a0bd877..4e4d66822b 100644
--- a/elf/enbl-secure.c
+++ b/elf/enbl-secure.c
@@ -26,15 +26,5 @@
 #include <startup.h>
 #include <libc-internal.h>
 
-/* If nonzero __libc_enable_secure is already set.  */
-int __libc_enable_secure_decided;
 /* Safest assumption, if somehow the initializer isn't run.  */
 int __libc_enable_secure = 1;
-
-void
-__libc_init_secure (void)
-{
-  if (__libc_enable_secure_decided == 0)
-    __libc_enable_secure = (startup_geteuid () != startup_getuid ()
-			    || startup_getegid () != startup_getgid ());
-}
diff --git a/include/libc-internal.h b/include/libc-internal.h
index 15920d2bde..c052bccb27 100644
--- a/include/libc-internal.h
+++ b/include/libc-internal.h
@@ -21,9 +21,6 @@
 
 #include <hp-timing.h>
 
-/* Initialize the `__libc_enable_secure' flag.  */
-extern void __libc_init_secure (void);
-
 /* Discover the tick frequency of the machine if something goes wrong,
    we return 0, an impossible hertz.  */
 extern int __profile_frequency (void);
diff --git a/include/unistd.h b/include/unistd.h
index 7090169601..af795a37c8 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -192,7 +192,6 @@ libc_hidden_proto (__tcsetpgrp)
    and some functions contained in the C library ignore various
    environment variables that normally affect them.  */
 extern int __libc_enable_secure attribute_relro;
-extern int __libc_enable_secure_decided;
 rtld_hidden_proto (__libc_enable_secure)
 
 
diff --git a/sysdeps/mach/hurd/enbl-secure.c b/sysdeps/mach/hurd/enbl-secure.c
deleted file mode 100644
index 8c02789ecf..0000000000
--- a/sysdeps/mach/hurd/enbl-secure.c
+++ /dev/null
@@ -1,30 +0,0 @@
-/* Define and initialize the `__libc_enable_secure' flag.  Hurd version.
-   Copyright (C) 1998-2022 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/>.  */
-
-/* There is no need for this file in the Hurd; it is just a placeholder
-   to prevent inclusion of the sysdeps/generic version.
-   In the shared library, the `__libc_enable_secure' variable is defined
-   by the dynamic linker in dl-sysdep.c and set there.
-   In the static library, it is defined in init-first.c and set there.  */
-
-#include <libc-internal.h>
-
-void
-__libc_init_secure (void)
-{
-}
diff --git a/sysdeps/unix/sysv/linux/i386/startup.h b/sysdeps/unix/sysv/linux/i386/startup.h
index aab8e26ca7..67c9310f3a 100644
--- a/sysdeps/unix/sysv/linux/i386/startup.h
+++ b/sysdeps/unix/sysv/linux/i386/startup.h
@@ -32,30 +32,6 @@ _startup_fatal (const char *message __attribute__ ((unused)))
   ABORT_INSTRUCTION;
   __builtin_unreachable ();
 }
-
-static inline uid_t
-startup_getuid (void)
-{
-  return (uid_t) INTERNAL_SYSCALL_CALL (getuid32);
-}
-
-static inline uid_t
-startup_geteuid (void)
-{
-  return (uid_t) INTERNAL_SYSCALL_CALL (geteuid32);
-}
-
-static inline gid_t
-startup_getgid (void)
-{
-  return (gid_t) INTERNAL_SYSCALL_CALL (getgid32);
-}
-
-static inline gid_t
-startup_getegid (void)
-{
-  return (gid_t) INTERNAL_SYSCALL_CALL (getegid32);
-}
 #else
 # include_next <startup.h>
 #endif
-- 
2.36.0.rc0.470.gd361397f0d-goog

Re: [PATCH] elf: Remove __libc_init_secure

[Florian Weimer]

* Fangrui Song:

> After 73fc4e28b9464f0e13edc719a5372839970e7ddb,
> __libc_enable_secure_decided is always 0 and a statically linked
> executable may overwrite __libc_enable_secure with a value not
> considering AT_SECURE.
>
> The __libc_enable_secure has been correctly initialized in _dl_aux_init,
> so just remove __libc_enable_secure_decided and __libc_init_secure.
> This allows us to remove some linux/i386 functions from
> 22b79ed7f413cd980a7af0cf258da5bf82b6d5e5.

This causes a build failure on Hurd:

/home/bmg/install/compilers/i686-gnu/lib/gcc/i686-glibc-gnu/11.2.1/../../../../i686-glibc-gnu/bin/ld: /home/bmg/build/glibcs/i686-gnu/glibc/libc.a(init-first.o):/home/bmg/src/glibc/csu/../sysdeps/mach/hurd/i386/init-first.c:42: multiple definition of `__libc_enable_secure'; /home/bmg/build/glibcs/i686-gnu/glibc/libc.a(enbl-secure.o):/home/bmg/src/glibc/elf/enbl-secure.c:30: first defined here

I think you need to remove the definition from init-first.c.

You can also remove the startup_get*id definitions from
sysdeps/generic/startup.h because they are unused after these changes.

Thanks,
Florian