lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame] | 1 | /* Map in a shared object's segments. Generic version. |
| 2 | Copyright (C) 1995-2015 Free Software Foundation, Inc. |
| 3 | This file is part of the GNU C Library. |
| 4 | |
| 5 | The GNU C Library is free software; you can redistribute it and/or |
| 6 | modify it under the terms of the GNU Lesser General Public |
| 7 | License as published by the Free Software Foundation; either |
| 8 | version 2.1 of the License, or (at your option) any later version. |
| 9 | |
| 10 | The GNU C Library is distributed in the hope that it will be useful, |
| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 13 | Lesser General Public License for more details. |
| 14 | |
| 15 | You should have received a copy of the GNU Lesser General Public |
| 16 | License along with the GNU C Library; if not, see |
| 17 | <http://www.gnu.org/licenses/>. */ |
| 18 | |
| 19 | #include <dl-load.h> |
| 20 | |
| 21 | /* This implementation assumes (as does the corresponding implementation |
| 22 | of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects |
| 23 | are always laid out with all segments contiguous (or with gaps |
| 24 | between them small enough that it's preferable to reserve all whole |
| 25 | pages inside the gaps with PROT_NONE mappings rather than permitting |
| 26 | other use of those parts of the address space). */ |
| 27 | |
| 28 | static __always_inline const char * |
| 29 | _dl_map_segments (struct link_map *l, int fd, |
| 30 | const ElfW(Ehdr) *header, int type, |
| 31 | const struct loadcmd loadcmds[], size_t nloadcmds, |
| 32 | const size_t maplength, bool has_holes, |
| 33 | struct link_map *loader) |
| 34 | { |
| 35 | const struct loadcmd *c = loadcmds; |
| 36 | |
| 37 | if (__glibc_likely (type == ET_DYN)) |
| 38 | { |
| 39 | /* This is a position-independent shared object. We can let the |
| 40 | kernel map it anywhere it likes, but we must have space for all |
| 41 | the segments in their specified positions relative to the first. |
| 42 | So we map the first segment without MAP_FIXED, but with its |
| 43 | extent increased to cover all the segments. Then we remove |
| 44 | access from excess portion, and there is known sufficient space |
| 45 | there to remap from the later segments. |
| 46 | |
| 47 | As a refinement, sometimes we have an address that we would |
| 48 | prefer to map such objects at; but this is only a preference, |
| 49 | the OS can do whatever it likes. */ |
| 50 | ElfW(Addr) mappref |
| 51 | = (ELF_PREFERRED_ADDRESS (loader, maplength, |
| 52 | c->mapstart & GLRO(dl_use_load_bias)) |
| 53 | - MAP_BASE_ADDR (l)); |
| 54 | |
| 55 | /* Remember which part of the address space this object uses. */ |
| 56 | l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength, |
| 57 | c->prot, |
| 58 | MAP_COPY|MAP_FILE, |
| 59 | fd, c->mapoff); |
| 60 | if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED)) |
| 61 | return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT; |
| 62 | |
| 63 | l->l_map_end = l->l_map_start + maplength; |
| 64 | l->l_addr = l->l_map_start - c->mapstart; |
| 65 | |
| 66 | if (has_holes) |
| 67 | /* Change protection on the excess portion to disallow all access; |
| 68 | the portions we do not remap later will be inaccessible as if |
| 69 | unallocated. Then jump into the normal segment-mapping loop to |
| 70 | handle the portion of the segment past the end of the file |
| 71 | mapping. */ |
| 72 | __mprotect ((caddr_t) (l->l_addr + c->mapend), |
| 73 | loadcmds[nloadcmds - 1].mapstart - c->mapend, |
| 74 | PROT_NONE); |
| 75 | |
| 76 | l->l_contiguous = 1; |
| 77 | |
| 78 | goto postmap; |
| 79 | } |
| 80 | |
| 81 | /* Remember which part of the address space this object uses. */ |
| 82 | l->l_map_start = c->mapstart + l->l_addr; |
| 83 | l->l_map_end = l->l_map_start + maplength; |
| 84 | l->l_contiguous = !has_holes; |
| 85 | |
| 86 | while (c < &loadcmds[nloadcmds]) |
| 87 | { |
| 88 | if (c->mapend > c->mapstart |
| 89 | /* Map the segment contents from the file. */ |
| 90 | && (__mmap ((void *) (l->l_addr + c->mapstart), |
| 91 | c->mapend - c->mapstart, c->prot, |
| 92 | MAP_FIXED|MAP_COPY|MAP_FILE, |
| 93 | fd, c->mapoff) |
| 94 | == MAP_FAILED)) |
| 95 | return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT; |
| 96 | |
| 97 | postmap: |
| 98 | _dl_postprocess_loadcmd (l, header, c); |
| 99 | |
| 100 | if (c->allocend > c->dataend) |
| 101 | { |
| 102 | /* Extra zero pages should appear at the end of this segment, |
| 103 | after the data mapped from the file. */ |
| 104 | ElfW(Addr) zero, zeroend, zeropage; |
| 105 | |
| 106 | zero = l->l_addr + c->dataend; |
| 107 | zeroend = l->l_addr + c->allocend; |
| 108 | zeropage = ((zero + GLRO(dl_pagesize) - 1) |
| 109 | & ~(GLRO(dl_pagesize) - 1)); |
| 110 | |
| 111 | if (zeroend < zeropage) |
| 112 | /* All the extra data is in the last page of the segment. |
| 113 | We can just zero it. */ |
| 114 | zeropage = zeroend; |
| 115 | |
| 116 | if (zeropage > zero) |
| 117 | { |
| 118 | /* Zero the final part of the last page of the segment. */ |
| 119 | if (__glibc_unlikely ((c->prot & PROT_WRITE) == 0)) |
| 120 | { |
| 121 | /* Dag nab it. */ |
| 122 | if (__mprotect ((caddr_t) (zero |
| 123 | & ~(GLRO(dl_pagesize) - 1)), |
| 124 | GLRO(dl_pagesize), c->prot|PROT_WRITE) < 0) |
| 125 | return DL_MAP_SEGMENTS_ERROR_MPROTECT; |
| 126 | } |
| 127 | memset ((void *) zero, '\0', zeropage - zero); |
| 128 | if (__glibc_unlikely ((c->prot & PROT_WRITE) == 0)) |
| 129 | __mprotect ((caddr_t) (zero & ~(GLRO(dl_pagesize) - 1)), |
| 130 | GLRO(dl_pagesize), c->prot); |
| 131 | } |
| 132 | |
| 133 | if (zeroend > zeropage) |
| 134 | { |
| 135 | /* Map the remaining zero pages in from the zero fill FD. */ |
| 136 | caddr_t mapat; |
| 137 | mapat = __mmap ((caddr_t) zeropage, zeroend - zeropage, |
| 138 | c->prot, MAP_ANON|MAP_PRIVATE|MAP_FIXED, |
| 139 | -1, 0); |
| 140 | if (__glibc_unlikely (mapat == MAP_FAILED)) |
| 141 | return DL_MAP_SEGMENTS_ERROR_MAP_ZERO_FILL; |
| 142 | } |
| 143 | } |
| 144 | |
| 145 | ++c; |
| 146 | } |
| 147 | |
| 148 | /* Notify ELF_PREFERRED_ADDRESS that we have to load this one |
| 149 | fixed. */ |
| 150 | ELF_FIXED_ADDRESS (loader, c->mapstart); |
| 151 | |
| 152 | return NULL; |
| 153 | } |