module-sections.c

  1/* SPDX-License-Identifier: GPL-2.0
  2 *
  3 * Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
  4 *
  5 * Copyright (C) 2018 Andes Technology Corporation <zong@andestech.com>
  6 */
  7
  8#include <linux/elf.h>
  9#include <linux/kernel.h>
 10#include <linux/module.h>
 11#include <linux/moduleloader.h>
 12#include <linux/sort.h>
 13
 14unsigned long module_emit_got_entry(struct module *mod, unsigned long val)
 15{
 16	struct mod_section *got_sec = &mod->arch.got;
 17	int i = got_sec->num_entries;
 18	struct got_entry *got = get_got_entry(val, got_sec);
 19
 20	if (got)
 21		return (unsigned long)got;
 22
 23	/* There is no duplicate entry, create a new one */
 24	got = (struct got_entry *)got_sec->shdr->sh_addr;
 25	got[i] = emit_got_entry(val);
 26
 27	got_sec->num_entries++;
 28	BUG_ON(got_sec->num_entries > got_sec->max_entries);
 29
 30	return (unsigned long)&got[i];
 31}
 32
 33unsigned long module_emit_plt_entry(struct module *mod, unsigned long val)
 34{
 35	struct mod_section *got_plt_sec = &mod->arch.got_plt;
 36	struct got_entry *got_plt;
 37	struct mod_section *plt_sec = &mod->arch.plt;
 38	struct plt_entry *plt = get_plt_entry(val, plt_sec, got_plt_sec);
 39	int i = plt_sec->num_entries;
 40
 41	if (plt)
 42		return (unsigned long)plt;
 43
 44	/* There is no duplicate entry, create a new one */
 45	got_plt = (struct got_entry *)got_plt_sec->shdr->sh_addr;
 46	got_plt[i] = emit_got_entry(val);
 47	plt = (struct plt_entry *)plt_sec->shdr->sh_addr;
 48	plt[i] = emit_plt_entry(val,
 49				(unsigned long)&plt[i],
 50				(unsigned long)&got_plt[i]);
 51
 52	plt_sec->num_entries++;
 53	got_plt_sec->num_entries++;
 54	BUG_ON(plt_sec->num_entries > plt_sec->max_entries);
 55
 56	return (unsigned long)&plt[i];
 57}
 58
 59#define cmp_3way(a, b)	((a) < (b) ? -1 : (a) > (b))
 60
 61static int cmp_rela(const void *a, const void *b)
 62{
 63	const Elf_Rela *x = a, *y = b;
 64	int i;
 65
 66	/* sort by type, symbol index and addend */
 67	i = cmp_3way(x->r_info, y->r_info);
 68	if (i == 0)
 69		i = cmp_3way(x->r_addend, y->r_addend);
 70	return i;
 71}
 72
 73static bool duplicate_rela(const Elf_Rela *rela, int idx)
 74{
 75	/*
 76	 * Entries are sorted by type, symbol index and addend. That means
 77	 * that, if a duplicate entry exists, it must be in the preceding slot.
 78	 */
 79	return idx > 0 && cmp_rela(rela + idx, rela + idx - 1) == 0;
 80}
 81
 82static void count_max_entries(const Elf_Rela *relas, size_t num,
 83			      unsigned int *plts, unsigned int *gots)
 84{
 85	for (size_t i = 0; i < num; i++) {
 86		if (duplicate_rela(relas, i))
 87			continue;
 88
 89		switch (ELF_R_TYPE(relas[i].r_info)) {
 90		case R_RISCV_CALL_PLT:
 91		case R_RISCV_PLT32:
 92			(*plts)++;
 93			break;
 94		case R_RISCV_GOT_HI20:
 95			(*gots)++;
 96			break;
 97		default:
 98			unreachable();
 99		}
100	}
101}
102
103static bool rela_needs_plt_got_entry(const Elf_Rela *rela)
104{
105	switch (ELF_R_TYPE(rela->r_info)) {
106	case R_RISCV_CALL_PLT:
107	case R_RISCV_GOT_HI20:
108	case R_RISCV_PLT32:
109		return true;
110	default:
111		return false;
112	}
113}
114
115int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
116			      char *secstrings, struct module *mod)
117{
118	size_t num_scratch_relas = 0;
119	unsigned int num_plts = 0;
120	unsigned int num_gots = 0;
121	Elf_Rela *scratch = NULL;
122	Elf_Rela *new_scratch;
123	size_t scratch_size = 0;
124	int i;
125
126	/*
127	 * Find the empty .got and .plt sections.
128	 */
129	for (i = 0; i < ehdr->e_shnum; i++) {
130		if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
131			mod->arch.plt.shdr = sechdrs + i;
132		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got"))
133			mod->arch.got.shdr = sechdrs + i;
134		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got.plt"))
135			mod->arch.got_plt.shdr = sechdrs + i;
136	}
137
138	if (!mod->arch.plt.shdr) {
139		pr_err("%s: module PLT section(s) missing\n", mod->name);
140		return -ENOEXEC;
141	}
142	if (!mod->arch.got.shdr) {
143		pr_err("%s: module GOT section(s) missing\n", mod->name);
144		return -ENOEXEC;
145	}
146	if (!mod->arch.got_plt.shdr) {
147		pr_err("%s: module GOT.PLT section(s) missing\n", mod->name);
148		return -ENOEXEC;
149	}
150
151	/* Calculate the maxinum number of entries */
152	for (i = 0; i < ehdr->e_shnum; i++) {
153		size_t num_relas = sechdrs[i].sh_size / sizeof(Elf_Rela);
154		Elf_Rela *relas = (void *)ehdr + sechdrs[i].sh_offset;
155		Elf_Shdr *dst_sec = sechdrs + sechdrs[i].sh_info;
156		size_t scratch_size_needed;
157
158		if (sechdrs[i].sh_type != SHT_RELA)
159			continue;
160
161		/* ignore relocations that operate on non-exec sections */
162		if (!(dst_sec->sh_flags & SHF_EXECINSTR))
163			continue;
164
165		/*
166		 * apply_relocate_add() relies on HI20 and LO12 relocation pairs being
167		 * close together, so sort a copy of the section to avoid interfering.
168		 */
169		scratch_size_needed = (num_scratch_relas + num_relas) * sizeof(*scratch);
170		if (scratch_size_needed > scratch_size) {
171			scratch_size = scratch_size_needed;
172			new_scratch = kvrealloc(scratch, scratch_size, GFP_KERNEL);
173			if (!new_scratch) {
174				kvfree(scratch);
175				return -ENOMEM;
176			}
177			scratch = new_scratch;
178		}
179
180		for (size_t j = 0; j < num_relas; j++)
181			if (rela_needs_plt_got_entry(&relas[j]))
182				scratch[num_scratch_relas++] = relas[j];
183	}
184
185	if (scratch) {
186		/* sort the accumulated PLT/GOT relocations so duplicates are adjacent */
187		sort(scratch, num_scratch_relas, sizeof(*scratch), cmp_rela, NULL);
188		count_max_entries(scratch, num_scratch_relas, &num_plts, &num_gots);
189		kvfree(scratch);
190	}
191
192	mod->arch.plt.shdr->sh_type = SHT_NOBITS;
193	mod->arch.plt.shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
194	mod->arch.plt.shdr->sh_addralign = L1_CACHE_BYTES;
195	mod->arch.plt.shdr->sh_size = (num_plts + 1) * sizeof(struct plt_entry);
196	mod->arch.plt.num_entries = 0;
197	mod->arch.plt.max_entries = num_plts;
198
199	mod->arch.got.shdr->sh_type = SHT_NOBITS;
200	mod->arch.got.shdr->sh_flags = SHF_ALLOC;
201	mod->arch.got.shdr->sh_addralign = L1_CACHE_BYTES;
202	mod->arch.got.shdr->sh_size = (num_gots + 1) * sizeof(struct got_entry);
203	mod->arch.got.num_entries = 0;
204	mod->arch.got.max_entries = num_gots;
205
206	mod->arch.got_plt.shdr->sh_type = SHT_NOBITS;
207	mod->arch.got_plt.shdr->sh_flags = SHF_ALLOC;
208	mod->arch.got_plt.shdr->sh_addralign = L1_CACHE_BYTES;
209	mod->arch.got_plt.shdr->sh_size = (num_plts + 1) * sizeof(struct got_entry);
210	mod->arch.got_plt.num_entries = 0;
211	mod->arch.got_plt.max_entries = num_plts;
212	return 0;
213}