1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
4 */
5
6 #include <linux/elf.h>
7 #include <linux/ftrace.h>
8 #include <linux/kernel.h>
9 #include <linux/module.h>
10 #include <linux/moduleloader.h>
11 #include <linux/sort.h>
12
13 static struct plt_entry __get_adrp_add_pair(u64 dst, u64 pc,
14 enum aarch64_insn_register reg)
15 {
16 u32 adrp, add;
17
18 adrp = aarch64_insn_gen_adr(pc, dst, reg, AARCH64_INSN_ADR_TYPE_ADRP);
19 add = aarch64_insn_gen_add_sub_imm(reg, reg, dst % SZ_4K,
20 AARCH64_INSN_VARIANT_64BIT,
21 AARCH64_INSN_ADSB_ADD);
22
23 return (struct plt_entry){ cpu_to_le32(adrp), cpu_to_le32(add) };
24 }
25
26 struct plt_entry get_plt_entry(u64 dst, void *pc)
27 {
28 struct plt_entry plt;
29 static u32 br;
30
31 if (!br)
32 br = aarch64_insn_gen_branch_reg(AARCH64_INSN_REG_16,
33 AARCH64_INSN_BRANCH_NOLINK);
34
35 plt = __get_adrp_add_pair(dst, (u64)pc, AARCH64_INSN_REG_16);
36 plt.br = cpu_to_le32(br);
37
38 return plt;
39 }
40
41 static bool plt_entries_equal(const struct plt_entry *a,
42 const struct plt_entry *b)
43 {
44 u64 p, q;
45
46 /*
47 * Check whether both entries refer to the same target:
48 * do the cheapest checks first.
49 * If the 'add' or 'br' opcodes are different, then the target
50 * cannot be the same.
51 */
52 if (a->add != b->add || a->br != b->br)
53 return false;
54
55 p = ALIGN_DOWN((u64)a, SZ_4K);
56 q = ALIGN_DOWN((u64)b, SZ_4K);
57
58 /*
59 * If the 'adrp' opcodes are the same then we just need to check
60 * that they refer to the same 4k region.
61 */
62 if (a->adrp == b->adrp && p == q)
63 return true;
64
65 return (p + aarch64_insn_adrp_get_offset(le32_to_cpu(a->adrp))) ==
66 (q + aarch64_insn_adrp_get_offset(le32_to_cpu(b->adrp)));
67 }
68
69 u64 module_emit_plt_entry(struct module *mod, Elf64_Shdr *sechdrs,
70 void *loc, const Elf64_Rela *rela,
71 Elf64_Sym *sym)
72 {
73 struct mod_plt_sec *pltsec = !within_module_init((unsigned long)loc, mod) ?
74 &mod->arch.core : &mod->arch.init;
75 struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr;
76 int i = pltsec->plt_num_entries;
77 int j = i - 1;
78 u64 val = sym->st_value + rela->r_addend;
79
80 if (is_forbidden_offset_for_adrp(&plt[i].adrp))
81 i++;
82
83 plt[i] = get_plt_entry(val, &plt[i]);
84
85 /*
86 * Check if the entry we just created is a duplicate. Given that the
87 * relocations are sorted, this will be the last entry we allocated.
88 * (if one exists).
89 */
90 if (j >= 0 && plt_entries_equal(plt + i, plt + j))
91 return (u64)&plt[j];
92
93 pltsec->plt_num_entries += i - j;
94 if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
95 return 0;
96
97 return (u64)&plt[i];
98 }
99
100 #ifdef CONFIG_ARM64_ERRATUM_843419
101 u64 module_emit_veneer_for_adrp(struct module *mod, Elf64_Shdr *sechdrs,
102 void *loc, u64 val)
103 {
104 struct mod_plt_sec *pltsec = !within_module_init((unsigned long)loc, mod) ?
105 &mod->arch.core : &mod->arch.init;
106 struct plt_entry *plt = (struct plt_entry *)sechdrs[pltsec->plt_shndx].sh_addr;
107 int i = pltsec->plt_num_entries++;
108 u32 br;
109 int rd;
110
111 if (WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries))
112 return 0;
113
114 if (is_forbidden_offset_for_adrp(&plt[i].adrp))
115 i = pltsec->plt_num_entries++;
116
117 /* get the destination register of the ADRP instruction */
118 rd = aarch64_insn_decode_register(AARCH64_INSN_REGTYPE_RD,
119 le32_to_cpup((__le32 *)loc));
120
121 br = aarch64_insn_gen_branch_imm((u64)&plt[i].br, (u64)loc + 4,
122 AARCH64_INSN_BRANCH_NOLINK);
123
124 plt[i] = __get_adrp_add_pair(val, (u64)&plt[i], rd);
125 plt[i].br = cpu_to_le32(br);
126
127 return (u64)&plt[i];
128 }
129 #endif
130
131 #define cmp_3way(a, b) ((a) < (b) ? -1 : (a) > (b))
132
133 static int cmp_rela(const void *a, const void *b)
134 {
135 const Elf64_Rela *x = a, *y = b;
136 int i;
137
138 /* sort by type, symbol index and addend */
139 i = cmp_3way(ELF64_R_TYPE(x->r_info), ELF64_R_TYPE(y->r_info));
140 if (i == 0)
141 i = cmp_3way(ELF64_R_SYM(x->r_info), ELF64_R_SYM(y->r_info));
142 if (i == 0)
143 i = cmp_3way(x->r_addend, y->r_addend);
144 return i;
145 }
146
147 static bool duplicate_rel(const Elf64_Rela *rela, int num)
148 {
149 /*
150 * Entries are sorted by type, symbol index and addend. That means
151 * that, if a duplicate entry exists, it must be in the preceding
152 * slot.
153 */
154 return num > 0 && cmp_rela(rela + num, rela + num - 1) == 0;
155 }
156
157 static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int num,
158 Elf64_Word dstidx, Elf_Shdr *dstsec)
159 {
160 unsigned int ret = 0;
161 Elf64_Sym *s;
162 int i;
163
164 for (i = 0; i < num; i++) {
165 u64 min_align;
166
167 switch (ELF64_R_TYPE(rela[i].r_info)) {
168 case R_AARCH64_JUMP26:
169 case R_AARCH64_CALL26:
170 /*
171 * We only have to consider branch targets that resolve
172 * to symbols that are defined in a different section.
173 * This is not simply a heuristic, it is a fundamental
174 * limitation, since there is no guaranteed way to emit
175 * PLT entries sufficiently close to the branch if the
176 * section size exceeds the range of a branch
177 * instruction. So ignore relocations against defined
178 * symbols if they live in the same section as the
179 * relocation target.
180 */
181 s = syms + ELF64_R_SYM(rela[i].r_info);
182 if (s->st_shndx == dstidx)
183 break;
184
185 /*
186 * Jump relocations with non-zero addends against
187 * undefined symbols are supported by the ELF spec, but
188 * do not occur in practice (e.g., 'jump n bytes past
189 * the entry point of undefined function symbol f').
190 * So we need to support them, but there is no need to
191 * take them into consideration when trying to optimize
192 * this code. So let's only check for duplicates when
193 * the addend is zero: this allows us to record the PLT
194 * entry address in the symbol table itself, rather than
195 * having to search the list for duplicates each time we
196 * emit one.
197 */
198 if (rela[i].r_addend != 0 || !duplicate_rel(rela, i))
199 ret++;
200 break;
201 case R_AARCH64_ADR_PREL_PG_HI21_NC:
202 case R_AARCH64_ADR_PREL_PG_HI21:
203 if (!cpus_have_final_cap(ARM64_WORKAROUND_843419))
204 break;
205
206 /*
207 * Determine the minimal safe alignment for this ADRP
208 * instruction: the section alignment at which it is
209 * guaranteed not to appear at a vulnerable offset.
210 *
211 * This comes down to finding the least significant zero
212 * bit in bits [11:3] of the section offset, and
213 * increasing the section's alignment so that the
214 * resulting address of this instruction is guaranteed
215 * to equal the offset in that particular bit (as well
216 * as all less significant bits). This ensures that the
217 * address modulo 4 KB != 0xfff8 or 0xfffc (which would
218 * have all ones in bits [11:3])
219 */
220 min_align = 2ULL << ffz(rela[i].r_offset | 0x7);
221
222 /*
223 * Allocate veneer space for each ADRP that may appear
224 * at a vulnerable offset nonetheless. At relocation
225 * time, some of these will remain unused since some
226 * ADRP instructions can be patched to ADR instructions
227 * instead.
228 */
229 if (min_align > SZ_4K)
230 ret++;
231 else
232 dstsec->sh_addralign = max(dstsec->sh_addralign,
233 min_align);
234 break;
235 }
236 }
237
238 if (cpus_have_final_cap(ARM64_WORKAROUND_843419)) {
239 /*
240 * Add some slack so we can skip PLT slots that may trigger
241 * the erratum due to the placement of the ADRP instruction.
242 */
243 ret += DIV_ROUND_UP(ret, (SZ_4K / sizeof(struct plt_entry)));
244 }
245
246 return ret;
247 }
248
249 static bool branch_rela_needs_plt(Elf64_Sym *syms, Elf64_Rela *rela,
250 Elf64_Word dstidx)
251 {
252
253 Elf64_Sym *s = syms + ELF64_R_SYM(rela->r_info);
254
255 if (s->st_shndx == dstidx)
256 return false;
257
258 return ELF64_R_TYPE(rela->r_info) == R_AARCH64_JUMP26 ||
259 ELF64_R_TYPE(rela->r_info) == R_AARCH64_CALL26;
260 }
261
262 /* Group branch PLT relas at the front end of the array. */
263 static int partition_branch_plt_relas(Elf64_Sym *syms, Elf64_Rela *rela,
264 int numrels, Elf64_Word dstidx)
265 {
266 int i = 0, j = numrels - 1;
267
268 while (i < j) {
269 if (branch_rela_needs_plt(syms, &rela[i], dstidx))
270 i++;
271 else if (branch_rela_needs_plt(syms, &rela[j], dstidx))
272 swap(rela[i], rela[j]);
273 else
274 j--;
275 }
276
277 return i;
278 }
279
280 int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
281 char *secstrings, struct module *mod)
282 {
283 unsigned long core_plts = 0;
284 unsigned long init_plts = 0;
285 Elf64_Sym *syms = NULL;
286 Elf_Shdr *pltsec, *tramp = NULL;
287 int i;
288
289 /*
290 * Find the empty .plt section so we can expand it to store the PLT
291 * entries. Record the symtab address as well.
292 */
293 for (i = 0; i < ehdr->e_shnum; i++) {
294 if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
295 mod->arch.core.plt_shndx = i;
296 else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt"))
297 mod->arch.init.plt_shndx = i;
298 else if (!strcmp(secstrings + sechdrs[i].sh_name,
299 ".text.ftrace_trampoline"))
300 tramp = sechdrs + i;
301 else if (sechdrs[i].sh_type == SHT_SYMTAB)
302 syms = (Elf64_Sym *)sechdrs[i].sh_addr;
303 }
304
305 if (!mod->arch.core.plt_shndx || !mod->arch.init.plt_shndx) {
306 pr_err("%s: module PLT section(s) missing\n", mod->name);
307 return -ENOEXEC;
308 }
309 if (!syms) {
310 pr_err("%s: module symtab section missing\n", mod->name);
311 return -ENOEXEC;
312 }
313
314 for (i = 0; i < ehdr->e_shnum; i++) {
315 Elf64_Rela *rels = (void *)ehdr + sechdrs[i].sh_offset;
316 int nents, numrels = sechdrs[i].sh_size / sizeof(Elf64_Rela);
317 Elf64_Shdr *dstsec = sechdrs + sechdrs[i].sh_info;
318
319 if (sechdrs[i].sh_type != SHT_RELA)
320 continue;
321
322 /* ignore relocations that operate on non-exec sections */
323 if (!(dstsec->sh_flags & SHF_EXECINSTR))
324 continue;
325
326 /*
327 * sort branch relocations requiring a PLT by type, symbol index
328 * and addend
329 */
330 nents = partition_branch_plt_relas(syms, rels, numrels,
331 sechdrs[i].sh_info);
332 if (nents)
333 sort(rels, nents, sizeof(Elf64_Rela), cmp_rela, NULL);
334
335 if (!module_init_layout_section(secstrings + dstsec->sh_name))
336 core_plts += count_plts(syms, rels, numrels,
337 sechdrs[i].sh_info, dstsec);
338 else
339 init_plts += count_plts(syms, rels, numrels,
340 sechdrs[i].sh_info, dstsec);
341 }
342
343 pltsec = sechdrs + mod->arch.core.plt_shndx;
344 pltsec->sh_type = SHT_NOBITS;
345 pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
346 pltsec->sh_addralign = L1_CACHE_BYTES;
347 pltsec->sh_size = (core_plts + 1) * sizeof(struct plt_entry);
348 mod->arch.core.plt_num_entries = 0;
349 mod->arch.core.plt_max_entries = core_plts;
350
351 pltsec = sechdrs + mod->arch.init.plt_shndx;
352 pltsec->sh_type = SHT_NOBITS;
353 pltsec->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
354 pltsec->sh_addralign = L1_CACHE_BYTES;
355 pltsec->sh_size = (init_plts + 1) * sizeof(struct plt_entry);
356 mod->arch.init.plt_num_entries = 0;
357 mod->arch.init.plt_max_entries = init_plts;
358
359 if (tramp) {
360 tramp->sh_type = SHT_NOBITS;
361 tramp->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
362 tramp->sh_addralign = __alignof__(struct plt_entry);
363 tramp->sh_size = NR_FTRACE_PLTS * sizeof(struct plt_entry);
364 }
365
366 return 0;
367 }
368
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