module-sections.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
  4 */
  5
  6#include <linux/elf.h>
  7#include <linux/kernel.h>
  8#include <linux/module.h>
  9#include <linux/moduleloader.h>
 10#include <linux/ftrace.h>
 11#include <linux/sort.h>
 12
 13Elf_Addr module_emit_got_entry(struct module *mod, Elf_Shdr *sechdrs, Elf_Addr val)
 14{
 15	struct mod_section *got_sec = &mod->arch.got;
 16	int i = got_sec->num_entries;
 17	struct got_entry *got = get_got_entry(val, sechdrs, got_sec);
 18
 19	if (got)
 20		return (Elf_Addr)got;
 21
 22	/* There is no GOT entry for val yet, create a new one. */
 23	got = (struct got_entry *)sechdrs[got_sec->shndx].sh_addr;
 24	got[i] = emit_got_entry(val);
 25
 26	got_sec->num_entries++;
 27	if (got_sec->num_entries > got_sec->max_entries) {
 28		/*
 29		 * This may happen when the module contains a GOT_HI20 without
 30		 * a paired GOT_LO12. Such a module is broken, reject it.
 31		 */
 32		pr_err("%s: module contains bad GOT relocation\n", mod->name);
 33		return 0;
 34	}
 35
 36	return (Elf_Addr)&got[i];
 37}
 38
 39Elf_Addr module_emit_plt_entry(struct module *mod, Elf_Shdr *sechdrs, Elf_Addr val)
 40{
 41	int nr;
 42	struct mod_section *plt_sec = &mod->arch.plt;
 43	struct mod_section *plt_idx_sec = &mod->arch.plt_idx;
 44	struct plt_entry *plt = get_plt_entry(val, sechdrs, plt_sec, plt_idx_sec);
 45	struct plt_idx_entry *plt_idx;
 46
 47	if (plt)
 48		return (Elf_Addr)plt;
 49
 50	nr = plt_sec->num_entries;
 51
 52	/* There is no duplicate entry, create a new one */
 53	plt = (struct plt_entry *)sechdrs[plt_sec->shndx].sh_addr;
 54	plt[nr] = emit_plt_entry(val);
 55	plt_idx = (struct plt_idx_entry *)sechdrs[plt_idx_sec->shndx].sh_addr;
 56	plt_idx[nr] = emit_plt_idx_entry(val);
 57
 58	plt_sec->num_entries++;
 59	plt_idx_sec->num_entries++;
 60	BUG_ON(plt_sec->num_entries > plt_sec->max_entries);
 61
 62	return (Elf_Addr)&plt[nr];
 63}
 64
 65#define cmp_3way(a, b)  ((a) < (b) ? -1 : (a) > (b))
 66
 67static int compare_rela(const void *x, const void *y)
 68{
 69	int ret;
 70	const Elf_Rela *rela_x = x, *rela_y = y;
 71
 72	ret = cmp_3way(rela_x->r_info, rela_y->r_info);
 73	if (ret == 0)
 74		ret = cmp_3way(rela_x->r_addend, rela_y->r_addend);
 75
 76	return ret;
 77}
 78
 79static void count_max_entries(Elf_Rela *relas, int num,
 80			      unsigned int *plts, unsigned int *gots)
 81{
 82	unsigned int i;
 83
 84	sort(relas, num, sizeof(Elf_Rela), compare_rela, NULL);
 85
 86	for (i = 0; i < num; i++) {
 87		if (i && !compare_rela(&relas[i-1], &relas[i]))
 88			continue;
 89
 90		switch (ELF_R_TYPE(relas[i].r_info)) {
 91		case R_LARCH_SOP_PUSH_PLT_PCREL:
 92		case R_LARCH_B26:
 93			(*plts)++;
 94			break;
 95		case R_LARCH_GOT_PC_HI20:
 96		case R_LARCH_GOT_PCADD_HI20:
 97			(*gots)++;
 98			break;
 99		default:
100			break; /* Do nothing. */
101		}
102	}
103}
104
105int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
106			      char *secstrings, struct module *mod)
107{
108	unsigned int i, num_plts = 0, num_gots = 0;
109	Elf_Shdr *got_sec, *plt_sec, *plt_idx_sec, *tramp = NULL;
110
111	/*
112	 * Find the empty .plt sections.
113	 */
114	for (i = 0; i < ehdr->e_shnum; i++) {
115		if (!strcmp(secstrings + sechdrs[i].sh_name, ".got"))
116			mod->arch.got.shndx = i;
117		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
118			mod->arch.plt.shndx = i;
119		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt.idx"))
120			mod->arch.plt_idx.shndx = i;
121		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".ftrace_trampoline"))
122			tramp = sechdrs + i;
123	}
124
125	if (!mod->arch.got.shndx) {
126		pr_err("%s: module GOT section(s) missing\n", mod->name);
127		return -ENOEXEC;
128	}
129	if (!mod->arch.plt.shndx) {
130		pr_err("%s: module PLT section(s) missing\n", mod->name);
131		return -ENOEXEC;
132	}
133	if (!mod->arch.plt_idx.shndx) {
134		pr_err("%s: module PLT.IDX section(s) missing\n", mod->name);
135		return -ENOEXEC;
136	}
137
138	/* Calculate the maxinum number of entries */
139	for (i = 0; i < ehdr->e_shnum; i++) {
140		int num_rela = sechdrs[i].sh_size / sizeof(Elf_Rela);
141		Elf_Rela *relas = (void *)ehdr + sechdrs[i].sh_offset;
142		Elf_Shdr *dst_sec = sechdrs + sechdrs[i].sh_info;
143
144		if (sechdrs[i].sh_type != SHT_RELA)
145			continue;
146
147		/* ignore relocations that operate on non-exec sections */
148		if (!(dst_sec->sh_flags & SHF_EXECINSTR))
149			continue;
150
151		count_max_entries(relas, num_rela, &num_plts, &num_gots);
152	}
153
154	got_sec = sechdrs + mod->arch.got.shndx;
155	got_sec->sh_type = SHT_NOBITS;
156	got_sec->sh_flags = SHF_ALLOC;
157	got_sec->sh_addralign = L1_CACHE_BYTES;
158	got_sec->sh_size = (num_gots + 1) * sizeof(struct got_entry);
159	mod->arch.got.num_entries = 0;
160	mod->arch.got.max_entries = num_gots;
161
162	plt_sec = sechdrs + mod->arch.plt.shndx;
163	plt_sec->sh_type = SHT_NOBITS;
164	plt_sec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
165	plt_sec->sh_addralign = L1_CACHE_BYTES;
166	plt_sec->sh_size = (num_plts + 1) * sizeof(struct plt_entry);
167	mod->arch.plt.num_entries = 0;
168	mod->arch.plt.max_entries = num_plts;
169
170	plt_idx_sec = sechdrs + mod->arch.plt_idx.shndx;
171	plt_idx_sec->sh_type = SHT_NOBITS;
172	plt_idx_sec->sh_flags = SHF_ALLOC;
173	plt_idx_sec->sh_addralign = L1_CACHE_BYTES;
174	plt_idx_sec->sh_size = (num_plts + 1) * sizeof(struct plt_idx_entry);
175	mod->arch.plt_idx.num_entries = 0;
176	mod->arch.plt_idx.max_entries = num_plts;
177
178	if (tramp) {
179		tramp->sh_type = SHT_NOBITS;
180		tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
181		tramp->sh_addralign = __alignof__(struct plt_entry);
182		tramp->sh_size = NR_FTRACE_PLTS * sizeof(struct plt_entry);
183	}
184
185	return 0;
186}