1 /*
2 * Stack-less Just-In-Time compiler
3 *
4 * Copyright Zoltan Herczeg (hzmester@freemail.hu). All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without modification, are
7 * permitted provided that the following conditions are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright notice, this list of
10 * conditions and the following disclaimer.
11 *
12 * 2. Redistributions in binary form must reproduce the above copyright notice, this list
13 * of conditions and the following disclaimer in the documentation and/or other materials
14 * provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) AND CONTRIBUTORS ``AS IS'' AND ANY
17 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
19 * SHALL THE COPYRIGHT HOLDER(S) OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
21 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
22 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
23 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
24 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27 /*
28 This file contains a simple W^X executable memory allocator
29
30 In *NIX, MAP_ANON is required (that is considered a feature) so make
31 sure to set the right availability macros for your system or the code
32 will fail to build.
33
34 If your system doesn't support mapping of anonymous pages (ex: IRIX) it
35 is also likely that it doesn't need this allocator and should be using
36 the standard one instead.
37
38 It allocates a separate map for each code block and may waste a lot of
39 memory, because whatever was requested, will be rounded up to the page
40 size (minimum 4KB, but could be even bigger).
41
42 It changes the page permissions (RW <-> RX) as needed and therefore, if you
43 will be updating the code after it has been generated, need to make sure to
44 block any concurrent execution, or could result in a SIGBUS, that could
45 even manifest itself at a different address than the one that was being
46 modified.
47
48 Only use if you are unable to use the regular allocator because of security
49 restrictions and adding exceptions to your application or the system are
50 not possible.
51 */
52
53 #include <sys/types.h>
54 #include <sys/mman.h>
55
56 #define SLJIT_UPDATE_WX_FLAGS(from, to, enable_exec) \
57 sljit_update_wx_flags((from), (to), (enable_exec))
58
59 #if !(defined SLJIT_SINGLE_THREADED && SLJIT_SINGLE_THREADED)
60 #include <pthread.h>
61 #define SLJIT_SE_LOCK() pthread_mutex_lock(&se_lock)
62 #define SLJIT_SE_UNLOCK() pthread_mutex_unlock(&se_lock)
63 #else
64 #define SLJIT_SE_LOCK()
65 #define SLJIT_SE_UNLOCK()
66 #endif /* !SLJIT_SINGLE_THREADED */
67
68 #define SLJIT_WX_IS_BLOCK(ptr, size) generic_check_is_wx_block(ptr, size)
69
generic_check_is_wx_block(void * ptr,sljit_uw size)70 static SLJIT_INLINE int generic_check_is_wx_block(void *ptr, sljit_uw size)
71 {
72 if (SLJIT_LIKELY(!mprotect(ptr, size, PROT_EXEC)))
73 return !!mprotect(ptr, size, PROT_READ | PROT_WRITE);
74
75 return 1;
76 }
77
sljit_malloc_exec(sljit_uw size)78 SLJIT_API_FUNC_ATTRIBUTE void* sljit_malloc_exec(sljit_uw size)
79 {
80 #if !(defined SLJIT_SINGLE_THREADED && SLJIT_SINGLE_THREADED)
81 static pthread_mutex_t se_lock = PTHREAD_MUTEX_INITIALIZER;
82 #endif
83 static int wx_block = -1;
84 int prot = PROT_READ | PROT_WRITE;
85 sljit_uw* ptr;
86
87 if (SLJIT_UNLIKELY(wx_block > 0))
88 return NULL;
89
90 #ifdef PROT_MAX
91 prot |= PROT_MAX(PROT_READ | PROT_WRITE | PROT_EXEC);
92 #endif
93
94 size += sizeof(sljit_uw);
95 ptr = (sljit_uw*)mmap(NULL, size, prot, MAP_PRIVATE | MAP_ANON, -1, 0);
96
97 if (ptr == MAP_FAILED)
98 return NULL;
99
100 if (SLJIT_UNLIKELY(wx_block < 0)) {
101 SLJIT_SE_LOCK();
102 wx_block = SLJIT_WX_IS_BLOCK(ptr, size);
103 SLJIT_SE_UNLOCK();
104 if (SLJIT_UNLIKELY(wx_block)) {
105 munmap((void *)ptr, size);
106 return NULL;
107 }
108 }
109
110 *ptr++ = size;
111 return ptr;
112 }
113
114 #undef SLJIT_SE_UNLOCK
115 #undef SLJIT_SE_LOCK
116
sljit_free_exec(void * ptr)117 SLJIT_API_FUNC_ATTRIBUTE void sljit_free_exec(void* ptr)
118 {
119 sljit_uw *start_ptr = ((sljit_uw*)ptr) - 1;
120 munmap((void*)start_ptr, *start_ptr);
121 }
122
sljit_update_wx_flags(void * from,void * to,int enable_exec)123 static void sljit_update_wx_flags(void *from, void *to, int enable_exec)
124 {
125 sljit_uw page_mask = (sljit_uw)get_page_alignment();
126 sljit_uw start = (sljit_uw)from;
127 sljit_uw end = (sljit_uw)to;
128 int prot = PROT_READ | (enable_exec ? PROT_EXEC : PROT_WRITE);
129
130 SLJIT_ASSERT(start < end);
131
132 start &= ~page_mask;
133 end = (end + page_mask) & ~page_mask;
134
135 mprotect((void*)start, end - start, prot);
136 }
137
sljit_free_unused_memory_exec(void)138 SLJIT_API_FUNC_ATTRIBUTE void sljit_free_unused_memory_exec(void)
139 {
140 /* This allocator does not keep unused memory for future allocations. */
141 }
142
