1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
|
/*
* Copyright (C) 2014 Linaro Ltd. <ard.biesheuvel@linaro.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/elf.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sort.h>
#include <asm/cache.h>
#include <asm/opcodes.h>
#define PLT_ENT_STRIDE L1_CACHE_BYTES
#define PLT_ENT_COUNT (PLT_ENT_STRIDE / sizeof(u32))
#define PLT_ENT_SIZE (sizeof(struct plt_entries) / PLT_ENT_COUNT)
#ifdef CONFIG_THUMB2_KERNEL
#define PLT_ENT_LDR __opcode_to_mem_thumb32(0xf8dff000 | \
(PLT_ENT_STRIDE - 4))
#else
#define PLT_ENT_LDR __opcode_to_mem_arm(0xe59ff000 | \
(PLT_ENT_STRIDE - 8))
#endif
struct plt_entries {
u32 ldr[PLT_ENT_COUNT];
u32 lit[PLT_ENT_COUNT];
};
u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
{
struct plt_entries *plt, *plt_end;
int c;
plt = (void *)mod->arch.plt->sh_addr;
plt_end = (void *)plt + mod->arch.plt->sh_size;
/* Look for an existing entry pointing to 'val' */
for (c = mod->arch.plt_count; plt < plt_end; c -= PLT_ENT_COUNT, plt++) {
int i;
if (!c) {
/* Populate a new set of entries */
*plt = (struct plt_entries){
{ [0 ... PLT_ENT_COUNT - 1] = PLT_ENT_LDR, },
{ val, }
};
mod->arch.plt_count++;
return (u32)plt->ldr;
}
for (i = 0; i < PLT_ENT_COUNT; i++) {
if (!plt->lit[i]) {
plt->lit[i] = val;
mod->arch.plt_count++;
}
if (plt->lit[i] == val)
return (u32)&plt->ldr[i];
}
}
BUG();
}
#define cmp_3way(a,b) ((a) < (b) ? -1 : (a) > (b))
static int cmp_rel(const void *a, const void *b)
{
const Elf32_Rel *x = a, *y = b;
int i;
/* sort by type and symbol index */
i = cmp_3way(ELF32_R_TYPE(x->r_info), ELF32_R_TYPE(y->r_info));
if (i == 0)
i = cmp_3way(ELF32_R_SYM(x->r_info), ELF32_R_SYM(y->r_info));
return i;
}
static bool is_zero_addend_relocation(Elf32_Addr base, const Elf32_Rel *rel)
{
u32 *tval = (u32 *)(base + rel->r_offset);
/*
* Do a bitwise compare on the raw addend rather than fully decoding
* the offset and doing an arithmetic comparison.
* Note that a zero-addend jump/call relocation is encoded taking the
* PC bias into account, i.e., -8 for ARM and -4 for Thumb2.
*/
switch (ELF32_R_TYPE(rel->r_info)) {
u16 upper, lower;
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
upper = __mem_to_opcode_thumb16(((u16 *)tval)[0]);
lower = __mem_to_opcode_thumb16(((u16 *)tval)[1]);
return (upper & 0x7ff) == 0x7ff && (lower & 0x2fff) == 0x2ffe;
case R_ARM_CALL:
case R_ARM_PC24:
case R_ARM_JUMP24:
return (__mem_to_opcode_arm(*tval) & 0xffffff) == 0xfffffe;
}
BUG();
}
static bool duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num)
{
const Elf32_Rel *prev;
/*
* Entries are sorted by type and symbol index. That means that,
* if a duplicate entry exists, it must be in the preceding
* slot.
*/
if (!num)
return false;
prev = rel + num - 1;
return cmp_rel(rel + num, prev) == 0 &&
is_zero_addend_relocation(base, prev);
}
/* Count how many PLT entries we may need */
static unsigned int count_plts(const Elf32_Sym *syms, Elf32_Addr base,
const Elf32_Rel *rel, int num)
{
unsigned int ret = 0;
const Elf32_Sym *s;
int i;
for (i = 0; i < num; i++) {
switch (ELF32_R_TYPE(rel[i].r_info)) {
case R_ARM_CALL:
case R_ARM_PC24:
case R_ARM_JUMP24:
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
/*
* We only have to consider branch targets that resolve
* to undefined symbols. This is not simply a heuristic,
* it is a fundamental limitation, since the PLT itself
* is part of the module, and needs to be within range
* as well, so modules can never grow beyond that limit.
*/
s = syms + ELF32_R_SYM(rel[i].r_info);
if (s->st_shndx != SHN_UNDEF)
break;
/*
* Jump relocations with non-zero addends against
* undefined symbols are supported by the ELF spec, but
* do not occur in practice (e.g., 'jump n bytes past
* the entry point of undefined function symbol f').
* So we need to support them, but there is no need to
* take them into consideration when trying to optimize
* this code. So let's only check for duplicates when
* the addend is zero.
*/
if (!is_zero_addend_relocation(base, rel + i) ||
!duplicate_rel(base, rel, i))
ret++;
}
}
return ret;
}
int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
char *secstrings, struct module *mod)
{
unsigned long plts = 0;
Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;
Elf32_Sym *syms = NULL;
/*
* To store the PLTs, we expand the .text section for core module code
* and for initialization code.
*/
for (s = sechdrs; s < sechdrs_end; ++s) {
if (strcmp(".plt", secstrings + s->sh_name) == 0)
mod->arch.plt = s;
else if (s->sh_type == SHT_SYMTAB)
syms = (Elf32_Sym *)s->sh_addr;
}
if (!mod->arch.plt) {
pr_err("%s: module PLT section missing\n", mod->name);
return -ENOEXEC;
}
if (!syms) {
pr_err("%s: module symtab section missing\n", mod->name);
return -ENOEXEC;
}
for (s = sechdrs + 1; s < sechdrs_end; ++s) {
Elf32_Rel *rels = (void *)ehdr + s->sh_offset;
int numrels = s->sh_size / sizeof(Elf32_Rel);
Elf32_Shdr *dstsec = sechdrs + s->sh_info;
if (s->sh_type != SHT_REL)
continue;
/* ignore relocations that operate on non-exec sections */
if (!(dstsec->sh_flags & SHF_EXECINSTR))
continue;
/* sort by type and symbol index */
sort(rels, numrels, sizeof(Elf32_Rel), cmp_rel, NULL);
plts += count_plts(syms, dstsec->sh_addr, rels, numrels);
}
mod->arch.plt->sh_type = SHT_NOBITS;
mod->arch.plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
mod->arch.plt->sh_addralign = L1_CACHE_BYTES;
mod->arch.plt->sh_size = round_up(plts * PLT_ENT_SIZE,
sizeof(struct plt_entries));
mod->arch.plt_count = 0;
pr_debug("%s: plt=%x\n", __func__, mod->arch.plt->sh_size);
return 0;
}
|
