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47618209d0
glibc/csu/libc-start.c
Szabolcs Nagy 47618209d0 Use hidden visibility for early static PIE code 
Extern symbol access in position independent code usually involves GOT
indirection which needs RELATIVE reloc in a static linked PIE. (On
some targets this is avoided e.g. because the linker can relax a GOT
access to a pc-relative access, but this is not generally true.) Code
that runs before static PIE self relocation must avoid relying on
dynamic relocations which can be ensured by using hidden visibility.
However we cannot just make all symbols hidden:

On i386, all calls to IFUNC functions must go through PLT and calls to
hidden functions CANNOT go through PLT in PIE since EBX used in PIE PLT
may not be set up for local calls to hidden IFUNC functions.

This patch aims to make symbol references hidden in code that is used
before and by _dl_relocate_static_pie when building a static PIE libc.
Note: for an object that is used in the startup code, its references
and definition may not have consistent visibility: it is only forced
hidden in the startup code.

This is needed for fixing bug 27072.

Co-authored-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
2021-01-21 15:55:01 +00:00

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/* Copyright (C) 1998-2021 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/>. */
/* Mark symbols hidden in static PIE for early self relocation to work. */
#if BUILD_PIE_DEFAULT
# pragma GCC visibility push(hidden)
#endif
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <ldsodefs.h>
#include <exit-thread.h>
#include <libc-diag.h>
#include <libc-internal.h>
#include <elf/libc-early-init.h>
#include <stdbool.h>
#include <elf/dl-tunables.h>
extern void __libc_init_first (int argc, char **argv, char **envp);
#include <tls.h>
#ifndef SHARED
# include <dl-osinfo.h>
# ifndef THREAD_SET_STACK_GUARD
/* Only exported for architectures that don't store the stack guard canary
in thread local area. */
uintptr_t __stack_chk_guard attribute_relro;
# endif
# ifndef THREAD_SET_POINTER_GUARD
/* Only exported for architectures that don't store the pointer guard
value in thread local area. */
uintptr_t __pointer_chk_guard_local
attribute_relro attribute_hidden __attribute__ ((nocommon));
# endif
#endif
#ifdef HAVE_PTR_NTHREADS
/* We need atomic operations. */
# include <atomic.h>
#endif
#ifndef SHARED
# include <link.h>
# include <dl-irel.h>
# ifdef ELF_MACHINE_IRELA
# define IREL_T ElfW(Rela)
# define IPLT_START __rela_iplt_start
# define IPLT_END __rela_iplt_end
# define IREL elf_irela
# elif defined ELF_MACHINE_IREL
# define IREL_T ElfW(Rel)
# define IPLT_START __rel_iplt_start
# define IPLT_END __rel_iplt_end
# define IREL elf_irel
# endif
static void
apply_irel (void)
{
# ifdef IREL
/* We use weak references for these so that we'll still work with a linker
that doesn't define them. Such a linker doesn't support IFUNC at all
and so uses won't work, but a statically-linked program that doesn't
use any IFUNC symbols won't have a problem. */
extern const IREL_T IPLT_START[] __attribute__ ((weak));
extern const IREL_T IPLT_END[] __attribute__ ((weak));
for (const IREL_T *ipltent = IPLT_START; ipltent < IPLT_END; ++ipltent)
IREL (ipltent);
# endif
}
#endif
#ifdef LIBC_START_MAIN
# ifdef LIBC_START_DISABLE_INLINE
# define STATIC static
# else
# define STATIC static inline __attribute__ ((always_inline))
# endif
#else
# define STATIC
# define LIBC_START_MAIN __libc_start_main
#endif
#ifdef MAIN_AUXVEC_ARG
/* main gets passed a pointer to the auxiliary. */
# define MAIN_AUXVEC_DECL , void *
# define MAIN_AUXVEC_PARAM , auxvec
#else
# define MAIN_AUXVEC_DECL
# define MAIN_AUXVEC_PARAM
#endif
#ifndef ARCH_INIT_CPU_FEATURES
# define ARCH_INIT_CPU_FEATURES()
#endif
#include <libc-start.h>
STATIC int LIBC_START_MAIN (int (*main) (int, char **, char **
MAIN_AUXVEC_DECL),
int argc,
char **argv,
#ifdef LIBC_START_MAIN_AUXVEC_ARG
ElfW(auxv_t) *auxvec,
#endif
__typeof (main) init,
void (*fini) (void),
void (*rtld_fini) (void),
void *stack_end)
__attribute__ ((noreturn));
/* Note: the fini parameter is ignored here for shared library. It
is registered with __cxa_atexit. This had the disadvantage that
finalizers were called in more than one place. */
STATIC int
LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
int argc, char **argv,
#ifdef LIBC_START_MAIN_AUXVEC_ARG
ElfW(auxv_t) *auxvec,
#endif
__typeof (main) init,
void (*fini) (void),
void (*rtld_fini) (void), void *stack_end)
{
/* Result of the 'main' function. */
int result;
#ifndef SHARED
_dl_relocate_static_pie ();
char **ev = &argv[argc + 1];
__environ = ev;
/* Store the lowest stack address. This is done in ld.so if this is
the code for the DSO. */
__libc_stack_end = stack_end;
# ifdef HAVE_AUX_VECTOR
/* First process the auxiliary vector since we need to find the
program header to locate an eventually present PT_TLS entry. */
# ifndef LIBC_START_MAIN_AUXVEC_ARG
ElfW(auxv_t) *auxvec;
{
char **evp = ev;
while (*evp++ != NULL)
;
auxvec = (ElfW(auxv_t) *) evp;
}
# endif
_dl_aux_init (auxvec);
if (GL(dl_phdr) == NULL)
# endif
{
/* Starting from binutils-2.23, the linker will define the
magic symbol __ehdr_start to point to our own ELF header
if it is visible in a segment that also includes the phdrs.
So we can set up _dl_phdr and _dl_phnum even without any
information from auxv. */
extern const ElfW(Ehdr) __ehdr_start
# if BUILD_PIE_DEFAULT
__attribute__ ((visibility ("hidden")));
# else
__attribute__ ((weak, visibility ("hidden")));
if (&__ehdr_start != NULL)
# endif
{
assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
GL(dl_phdr) = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
GL(dl_phnum) = __ehdr_start.e_phnum;
}
}
/* Initialize very early so that tunables can use it. */
__libc_init_secure ();
__tunables_init (__environ);
ARCH_INIT_CPU_FEATURES ();
/* Perform IREL{,A} relocations. */
ARCH_SETUP_IREL ();
/* The stack guard goes into the TCB, so initialize it early. */
ARCH_SETUP_TLS ();
/* In some architectures, IREL{,A} relocations happen after TLS setup in
order to let IFUNC resolvers benefit from TCB information, e.g. powerpc's
hwcap and platform fields available in the TCB. */
ARCH_APPLY_IREL ();
/* Set up the stack checker's canary. */
uintptr_t stack_chk_guard = _dl_setup_stack_chk_guard (_dl_random);
# ifdef THREAD_SET_STACK_GUARD
THREAD_SET_STACK_GUARD (stack_chk_guard);
# else
__stack_chk_guard = stack_chk_guard;
# endif
# ifdef DL_SYSDEP_OSCHECK
{
/* 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. */
if (__pthread_initialize_minimal != NULL)
__pthread_initialize_minimal ();
/* Set up the pointer guard value. */
uintptr_t pointer_chk_guard = _dl_setup_pointer_guard (_dl_random,
stack_chk_guard);
# ifdef THREAD_SET_POINTER_GUARD
THREAD_SET_POINTER_GUARD (pointer_chk_guard);
# else
__pointer_chk_guard_local = pointer_chk_guard;
# endif
#endif /* !SHARED */
/* Register the destructor of the dynamic linker if there is any. */
if (__glibc_likely (rtld_fini != NULL))
__cxa_atexit ((void (*) (void *)) rtld_fini, NULL, NULL);
#ifndef SHARED
/* Perform early initialization. In the shared case, this function
is called from the dynamic loader as early as possible. */
__libc_early_init (true);
/* Call the initializer of the libc. This is only needed here if we
are compiling for the static library in which case we haven't
run the constructors in `_dl_start_user'. */
__libc_init_first (argc, argv, __environ);
/* Register the destructor of the program, if any. */
if (fini)
__cxa_atexit ((void (*) (void *)) fini, NULL, NULL);
/* Some security at this point. Prevent starting a SUID binary where
the standard file descriptors are not opened. We have to do this
only for statically linked applications since otherwise the dynamic
loader did the work already. */
if (__builtin_expect (__libc_enable_secure, 0))
__libc_check_standard_fds ();
#endif
/* Call the initializer of the program, if any. */
#ifdef SHARED
if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_IMPCALLS, 0))
GLRO(dl_debug_printf) ("\ninitialize program: %s\n\n", argv[0]);
#endif
if (init)
(*init) (argc, argv, __environ MAIN_AUXVEC_PARAM);
#ifdef SHARED
/* Auditing checkpoint: we have a new object. */
if (__glibc_unlikely (GLRO(dl_naudit) > 0))
{
struct audit_ifaces *afct = GLRO(dl_audit);
struct link_map *head = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
{
if (afct->preinit != NULL)
afct->preinit (&link_map_audit_state (head, cnt)->cookie);
afct = afct->next;
}
}
#endif
#ifdef SHARED
if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_IMPCALLS))
GLRO(dl_debug_printf) ("\ntransferring control: %s\n\n", argv[0]);
#endif
#ifndef SHARED
_dl_debug_initialize (0, LM_ID_BASE);
#endif
#ifdef HAVE_CLEANUP_JMP_BUF
/* Memory for the cancellation buffer. */
struct pthread_unwind_buf unwind_buf;
int not_first_call;
DIAG_PUSH_NEEDS_COMMENT;
#if __GNUC_PREREQ (7, 0)
/* This call results in a -Wstringop-overflow warning because struct
pthread_unwind_buf is smaller than jmp_buf. setjmp and longjmp
do not use anything beyond the common prefix (they never access
the saved signal mask), so that is a false positive. */
DIAG_IGNORE_NEEDS_COMMENT (11, "-Wstringop-overflow=");
#endif
not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf);
DIAG_POP_NEEDS_COMMENT;
if (__glibc_likely (! not_first_call))
{
struct pthread *self = THREAD_SELF;
/* Store old info. */
unwind_buf.priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
unwind_buf.priv.data.cleanup = THREAD_GETMEM (self, cleanup);
/* Store the new cleanup handler info. */
THREAD_SETMEM (self, cleanup_jmp_buf, &unwind_buf);
/* Run the program. */
result = main (argc, argv, __environ MAIN_AUXVEC_PARAM);
}
else
{
/* Remove the thread-local data. */
# ifdef SHARED
PTHFCT_CALL (ptr__nptl_deallocate_tsd, ());
# else
extern void __nptl_deallocate_tsd (void) __attribute ((weak));
__nptl_deallocate_tsd ();
# endif
/* One less thread. Decrement the counter. If it is zero we
terminate the entire process. */
result = 0;
# ifdef SHARED
unsigned int *ptr = __libc_pthread_functions.ptr_nthreads;
# ifdef PTR_DEMANGLE
PTR_DEMANGLE (ptr);
# endif
# else
extern unsigned int __nptl_nthreads __attribute ((weak));
unsigned int *const ptr = &__nptl_nthreads;
# endif
if (! atomic_decrement_and_test (ptr))
/* Not much left to do but to exit the thread, not the process. */
__exit_thread ();
}
#else
/* Nothing fancy, just call the function. */
result = main (argc, argv, __environ MAIN_AUXVEC_PARAM);
#endif
exit (result);
}
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