1 /*
2  * Copyright (C) 2008 The Android Open Source Project
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  *  * Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  *  * Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in
12  *    the documentation and/or other materials provided with the
13  *    distribution.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26  * SUCH DAMAGE.
27  */
28 /*
29  * libc_init_static.c
30  *
31  * The program startup function __libc_init() defined here is
32  * used for static executables only (i.e. those that don't depend
33  * on shared libraries). It is called from arch-$ARCH/bionic/crtbegin_static.S
34  * which is directly invoked by the kernel when the program is launched.
35  *
36  * The 'structors' parameter contains pointers to various initializer
37  * arrays that must be run before the program's 'main' routine is launched.
38  */
39 
40 #include <elf.h>
41 #include <errno.h>
42 #include <stddef.h>
43 #include <stdint.h>
44 #include <stdio.h>
45 #include <stdlib.h>
46 #include <sys/auxv.h>
47 #include <sys/mman.h>
48 
49 #include "libc_init_common.h"
50 #include "pthread_internal.h"
51 
52 #include "private/bionic_tls.h"
53 #include "private/KernelArgumentBlock.h"
54 
55 // Returns the address of the page containing address 'x'.
56 #define PAGE_START(x)  ((x) & PAGE_MASK)
57 
58 // Returns the address of the next page after address 'x', unless 'x' is
59 // itself at the start of a page.
60 #define PAGE_END(x)    PAGE_START((x) + (PAGE_SIZE-1))
61 
62 extern "C" int __cxa_atexit(void (*)(void *), void *, void *);
63 
call_array(void (** list)())64 static void call_array(void(**list)()) {
65   // First element is -1, list is null-terminated
66   while (*++list) {
67     (*list)();
68   }
69 }
70 
apply_gnu_relro()71 static void apply_gnu_relro() {
72   ElfW(Phdr)* phdr_start = reinterpret_cast<ElfW(Phdr)*>(getauxval(AT_PHDR));
73   unsigned long int phdr_ct = getauxval(AT_PHNUM);
74 
75   for (ElfW(Phdr)* phdr = phdr_start; phdr < (phdr_start + phdr_ct); phdr++) {
76     if (phdr->p_type != PT_GNU_RELRO) {
77       continue;
78     }
79 
80     ElfW(Addr) seg_page_start = PAGE_START(phdr->p_vaddr);
81     ElfW(Addr) seg_page_end = PAGE_END(phdr->p_vaddr + phdr->p_memsz);
82 
83     // Check return value here? What do we do if we fail?
84     mprotect(reinterpret_cast<void*>(seg_page_start), seg_page_end - seg_page_start, PROT_READ);
85   }
86 }
87 
__libc_init(void * raw_args,void (* onexit)(void)__unused,int (* slingshot)(int,char **,char **),structors_array_t const * const structors)88 __noreturn void __libc_init(void* raw_args,
89                             void (*onexit)(void) __unused,
90                             int (*slingshot)(int, char**, char**),
91                             structors_array_t const * const structors) {
92   KernelArgumentBlock args(raw_args);
93   __libc_init_tls(args);
94   __libc_init_common(args);
95 
96   apply_gnu_relro();
97 
98   // Several Linux ABIs don't pass the onexit pointer, and the ones that
99   // do never use it.  Therefore, we ignore it.
100 
101   call_array(structors->preinit_array);
102   call_array(structors->init_array);
103 
104   // The executable may have its own destructors listed in its .fini_array
105   // so we need to ensure that these are called when the program exits
106   // normally.
107   if (structors->fini_array != NULL) {
108     __cxa_atexit(__libc_fini,structors->fini_array,NULL);
109   }
110 
111   exit(slingshot(args.argc, args.argv, args.envp));
112 }
113