summaryrefslogtreecommitdiffstats
path: root/arch/arm/kernel/module-plts.c
blob: 097e2e201b9f0e33e0fbf2a6ffe93115876bd76c (plain)
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
/*
 * 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 <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];
};

static bool in_init(const struct module *mod, u32 addr)
{
	return addr - (u32)mod->module_init < mod->init_size;
}

u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val)
{
	struct plt_entries *plt, *plt_end;
	int c, *count;

	if (in_init(mod, loc)) {
		plt = (void *)mod->arch.init_plt->sh_addr;
		plt_end = (void *)plt + mod->arch.init_plt->sh_size;
		count = &mod->arch.init_plt_count;
	} else {
		plt = (void *)mod->arch.core_plt->sh_addr;
		plt_end = (void *)plt + mod->arch.core_plt->sh_size;
		count = &mod->arch.core_plt_count;
	}

	/* Look for an existing entry pointing to 'val' */
	for (c = *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, }
			};
			++*count;
			return (u32)plt->ldr;
		}
		for (i = 0; i < PLT_ENT_COUNT; i++) {
			if (!plt->lit[i]) {
				plt->lit[i] = val;
				++*count;
			}
			if (plt->lit[i] == val)
				return (u32)&plt->ldr[i];
		}
	}
	BUG();
}

static int duplicate_rel(Elf32_Addr base, const Elf32_Rel *rel, int num,
			   u32 mask)
{
	u32 *loc1, *loc2;
	int i;

	for (i = 0; i < num; i++) {
		if (rel[i].r_info != rel[num].r_info)
			continue;

		/*
		 * Identical relocation types against identical symbols can
		 * still result in different PLT entries if the addend in the
		 * place is different. So resolve the target of the relocation
		 * to compare the values.
		 */
		loc1 = (u32 *)(base + rel[i].r_offset);
		loc2 = (u32 *)(base + rel[num].r_offset);
		if (((*loc1 ^ *loc2) & mask) == 0)
			return 1;
	}
	return 0;
}

/* Count how many PLT entries we may need */
static unsigned int count_plts(Elf32_Addr base, const Elf32_Rel *rel, int num)
{
	unsigned int ret = 0;
	int i;

	/*
	 * Sure, this is order(n^2), but it's usually short, and not
	 * time critical
	 */
	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:
			if (!duplicate_rel(base, rel, i,
					   __opcode_to_mem_arm(0x00ffffff)))
				ret++;
			break;
#ifdef CONFIG_THUMB2_KERNEL
		case R_ARM_THM_CALL:
		case R_ARM_THM_JUMP24:
			if (!duplicate_rel(base, rel, i,
					   __opcode_to_mem_thumb32(0x07ff2fff)))
				ret++;
#endif
		}
	return ret;
}

int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
			      char *secstrings, struct module *mod)
{
	unsigned long core_plts = 0, init_plts = 0;
	Elf32_Shdr *s, *sechdrs_end = sechdrs + ehdr->e_shnum;

	/*
	 * To store the PLTs, we expand the .text section for core module code
	 * and the .init.text section for initialization code.
	 */
	for (s = sechdrs; s < sechdrs_end; ++s)
		if (strcmp(".core.plt", secstrings + s->sh_name) == 0)
			mod->arch.core_plt = s;
		else if (strcmp(".init.plt", secstrings + s->sh_name) == 0)
			mod->arch.init_plt = s;

	if (!mod->arch.core_plt || !mod->arch.init_plt) {
		pr_err("%s: sections missing\n", mod->name);
		return -ENOEXEC;
	}

	for (s = sechdrs + 1; s < sechdrs_end; ++s) {
		const 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;

		if (strstr(secstrings + s->sh_name, ".init"))
			init_plts += count_plts(dstsec->sh_addr, rels, numrels);
		else
			core_plts += count_plts(dstsec->sh_addr, rels, numrels);
	}

	mod->arch.core_plt->sh_type = SHT_NOBITS;
	mod->arch.core_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
	mod->arch.core_plt->sh_addralign = L1_CACHE_BYTES;
	mod->arch.core_plt->sh_size = round_up(core_plts * PLT_ENT_SIZE,
					       sizeof(struct plt_entries));
	mod->arch.core_plt_count = 0;

	mod->arch.init_plt->sh_type = SHT_NOBITS;
	mod->arch.init_plt->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
	mod->arch.init_plt->sh_addralign = L1_CACHE_BYTES;
	mod->arch.init_plt->sh_size = round_up(init_plts * PLT_ENT_SIZE,
					       sizeof(struct plt_entries));
	mod->arch.init_plt_count = 0;
	pr_debug("%s: core.plt=%x, init.plt=%x\n", __func__,
		 mod->arch.core_plt->sh_size, mod->arch.init_plt->sh_size);
	return 0;
}