1 /* Map in a shared object's segments. Generic version.
2 Copyright (C) 1995-2023 Free Software Foundation, Inc.
3 Copyright The GNU Toolchain Authors.
4 This file is part of the GNU C Library.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20 #include <dl-load.h>
21
22 /* Map a segment and align it properly. */
23
24 static __always_inline ElfW(Addr)
25 _dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
26 const size_t maplength, int fd)
27 {
28 if (__glibc_likely (c->mapalign <= GLRO(dl_pagesize)))
29 return (ElfW(Addr)) __mmap ((void *) mappref, maplength, c->prot,
30 MAP_COPY|MAP_FILE, fd, c->mapoff);
31
32 /* If the segment alignment > the page size, allocate enough space to
33 ensure that the segment can be properly aligned. */
34 ElfW(Addr) maplen = (maplength >= c->mapalign
35 ? (maplength + c->mapalign)
36 : (2 * c->mapalign));
37 ElfW(Addr) map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen,
38 PROT_NONE,
39 MAP_ANONYMOUS|MAP_COPY,
40 -1, 0);
41 if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
42 return map_start;
43
44 ElfW(Addr) map_start_aligned = ALIGN_UP (map_start, c->mapalign);
45 map_start_aligned = (ElfW(Addr)) __mmap ((void *) map_start_aligned,
46 maplength, c->prot,
47 MAP_COPY|MAP_FILE|MAP_FIXED,
48 fd, c->mapoff);
49 if (__glibc_unlikely ((void *) map_start_aligned == MAP_FAILED))
50 __munmap ((void *) map_start, maplen);
51 else
52 {
53 /* Unmap the unused regions. */
54 ElfW(Addr) delta = map_start_aligned - map_start;
55 if (delta)
56 __munmap ((void *) map_start, delta);
57 ElfW(Addr) map_end = map_start_aligned + maplength;
58 map_end = ALIGN_UP (map_end, GLRO(dl_pagesize));
59 delta = map_start + maplen - map_end;
60 if (delta)
61 __munmap ((void *) map_end, delta);
62 }
63
64 return map_start_aligned;
65 }
66
67 /* This implementation assumes (as does the corresponding implementation
68 of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects
69 are always laid out with all segments contiguous (or with gaps
70 between them small enough that it's preferable to reserve all whole
71 pages inside the gaps with PROT_NONE mappings rather than permitting
72 other use of those parts of the address space). */
73
74 static __always_inline const char *
75 _dl_map_segments (struct link_map *l, int fd,
76 const ElfW(Ehdr) *header, int type,
77 const struct loadcmd loadcmds[], size_t nloadcmds,
78 const size_t maplength, bool has_holes,
79 struct link_map *loader)
80 {
81 const struct loadcmd *c = loadcmds;
82
83 if (__glibc_likely (type == ET_DYN))
84 {
85 /* This is a position-independent shared object. We can let the
86 kernel map it anywhere it likes, but we must have space for all
87 the segments in their specified positions relative to the first.
88 So we map the first segment without MAP_FIXED, but with its
89 extent increased to cover all the segments. Then we remove
90 access from excess portion, and there is known sufficient space
91 there to remap from the later segments.
92
93 As a refinement, sometimes we have an address that we would
94 prefer to map such objects at; but this is only a preference,
95 the OS can do whatever it likes. */
96 ElfW(Addr) mappref
97 = (ELF_PREFERRED_ADDRESS (loader, maplength, c->mapstart)
98 - MAP_BASE_ADDR (l));
99
100 /* Remember which part of the address space this object uses. */
101 l->l_map_start = _dl_map_segment (c, mappref, maplength, fd);
102 if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED))
103 return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;
104
105 l->l_map_end = l->l_map_start + maplength;
106 l->l_addr = l->l_map_start - c->mapstart;
107
108 if (has_holes)
109 {
110 /* Change protection on the excess portion to disallow all access;
111 the portions we do not remap later will be inaccessible as if
112 unallocated. Then jump into the normal segment-mapping loop to
113 handle the portion of the segment past the end of the file
114 mapping. */
115 if (__glibc_unlikely (loadcmds[nloadcmds - 1].mapstart <
116 c->mapend))
117 return N_("ELF load command address/offset not page-aligned");
118 if (__glibc_unlikely
119 (__mprotect ((caddr_t) (l->l_addr + c->mapend),
120 loadcmds[nloadcmds - 1].mapstart - c->mapend,
121 PROT_NONE) < 0))
122 return DL_MAP_SEGMENTS_ERROR_MPROTECT;
123 }
124
125 l->l_contiguous = 1;
126
127 goto postmap;
128 }
129
130 /* Remember which part of the address space this object uses. */
131 l->l_map_start = c->mapstart + l->l_addr;
132 l->l_map_end = l->l_map_start + maplength;
133 l->l_contiguous = !has_holes;
134
135 while (c < &loadcmds[nloadcmds])
136 {
137 if (c->mapend > c->mapstart
138 /* Map the segment contents from the file. */
139 && (__mmap ((void *) (l->l_addr + c->mapstart),
140 c->mapend - c->mapstart, c->prot,
141 MAP_FIXED|MAP_COPY|MAP_FILE,
142 fd, c->mapoff)
143 == MAP_FAILED))
144 return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;
145
146 postmap:
147 _dl_postprocess_loadcmd (l, header, c);
148
149 if (c->allocend > c->dataend)
150 {
151 /* Extra zero pages should appear at the end of this segment,
152 after the data mapped from the file. */
153 ElfW(Addr) zero, zeroend, zeropage;
154
155 zero = l->l_addr + c->dataend;
156 zeroend = l->l_addr + c->allocend;
157 zeropage = ((zero + GLRO(dl_pagesize) - 1)
158 & ~(GLRO(dl_pagesize) - 1));
159
160 if (zeroend < zeropage)
161 /* All the extra data is in the last page of the segment.
162 We can just zero it. */
163 zeropage = zeroend;
164
165 if (zeropage > zero)
166 {
167 /* Zero the final part of the last page of the segment. */
168 if (__glibc_unlikely ((c->prot & PROT_WRITE) == 0))
169 {
170 /* Dag nab it. */
171 if (__mprotect ((caddr_t) (zero
172 & ~(GLRO(dl_pagesize) - 1)),
173 GLRO(dl_pagesize), c->prot|PROT_WRITE) < 0)
174 return DL_MAP_SEGMENTS_ERROR_MPROTECT;
175 }
176 memset ((void *) zero, '\0', zeropage - zero);
177 if (__glibc_unlikely ((c->prot & PROT_WRITE) == 0))
178 __mprotect ((caddr_t) (zero & ~(GLRO(dl_pagesize) - 1)),
179 GLRO(dl_pagesize), c->prot);
180 }
181
182 if (zeroend > zeropage)
183 {
184 /* Map the remaining zero pages in from the zero fill FD. */
185 caddr_t mapat;
186 mapat = __mmap ((caddr_t) zeropage, zeroend - zeropage,
187 c->prot, MAP_ANON|MAP_PRIVATE|MAP_FIXED,
188 -1, 0);
189 if (__glibc_unlikely (mapat == MAP_FAILED))
190 return DL_MAP_SEGMENTS_ERROR_MAP_ZERO_FILL;
191 }
192 }
193
194 ++c;
195 }
196
197 /* Notify ELF_PREFERRED_ADDRESS that we have to load this one
198 fixed. */
199 ELF_FIXED_ADDRESS (loader, c->mapstart);
200
201 return NULL;
202 }