1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * alternative runtime patching 4 * inspired by the x86 version 5 * 6 * Copyright (C) 2014 ARM Ltd. 7 */ 8 9 #define pr_fmt(fmt) "alternatives: " fmt 10 11 #include <linux/init.h> 12 #include <linux/cpu.h> 13 #include <linux/elf.h> 14 #include <asm/cacheflush.h> 15 #include <asm/alternative.h> 16 #include <asm/cpufeature.h> 17 #include <asm/insn.h> 18 #include <asm/module.h> 19 #include <asm/sections.h> 20 #include <asm/vdso.h> 21 #include <linux/stop_machine.h> 22 23 #define __ALT_PTR(a, f) ((void *)&(a)->f + (a)->f) 24 #define ALT_ORIG_PTR(a) __ALT_PTR(a, orig_offset) 25 #define ALT_REPL_PTR(a) __ALT_PTR(a, alt_offset) 26 27 #define ALT_CAP(a) ((a)->cpufeature & ~ARM64_CB_BIT) 28 #define ALT_HAS_CB(a) ((a)->cpufeature & ARM64_CB_BIT) 29 30 /* Volatile, as we may be patching the guts of READ_ONCE() */ 31 static volatile int all_alternatives_applied; 32 33 static DECLARE_BITMAP(applied_alternatives, ARM64_NCAPS); 34 35 struct alt_region { 36 struct alt_instr *begin; 37 struct alt_instr *end; 38 }; 39 40 bool alternative_is_applied(u16 cpufeature) 41 { 42 if (WARN_ON(cpufeature >= ARM64_NCAPS)) 43 return false; 44 45 return test_bit(cpufeature, applied_alternatives); 46 } 47 48 /* 49 * Check if the target PC is within an alternative block. 50 */ 51 static __always_inline bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc) 52 { 53 unsigned long replptr = (unsigned long)ALT_REPL_PTR(alt); 54 return !(pc >= replptr && pc <= (replptr + alt->alt_len)); 55 } 56 57 #define align_down(x, a) ((unsigned long)(x) & ~(((unsigned long)(a)) - 1)) 58 59 static __always_inline u32 get_alt_insn(struct alt_instr *alt, __le32 *insnptr, __le32 *altinsnptr) 60 { 61 u32 insn; 62 63 insn = le32_to_cpu(*altinsnptr); 64 65 if (aarch64_insn_is_branch_imm(insn)) { 66 s32 offset = aarch64_get_branch_offset(insn); 67 unsigned long target; 68 69 target = (unsigned long)altinsnptr + offset; 70 71 /* 72 * If we're branching inside the alternate sequence, 73 * do not rewrite the instruction, as it is already 74 * correct. Otherwise, generate the new instruction. 75 */ 76 if (branch_insn_requires_update(alt, target)) { 77 offset = target - (unsigned long)insnptr; 78 insn = aarch64_set_branch_offset(insn, offset); 79 } 80 } else if (aarch64_insn_is_adrp(insn)) { 81 s32 orig_offset, new_offset; 82 unsigned long target; 83 84 /* 85 * If we're replacing an adrp instruction, which uses PC-relative 86 * immediate addressing, adjust the offset to reflect the new 87 * PC. adrp operates on 4K aligned addresses. 88 */ 89 orig_offset = aarch64_insn_adrp_get_offset(insn); 90 target = align_down(altinsnptr, SZ_4K) + orig_offset; 91 new_offset = target - align_down(insnptr, SZ_4K); 92 insn = aarch64_insn_adrp_set_offset(insn, new_offset); 93 } else if (aarch64_insn_uses_literal(insn)) { 94 /* 95 * Disallow patching unhandled instructions using PC relative 96 * literal addresses 97 */ 98 BUG(); 99 } 100 101 return insn; 102 } 103 104 static noinstr void patch_alternative(struct alt_instr *alt, 105 __le32 *origptr, __le32 *updptr, int nr_inst) 106 { 107 __le32 *replptr; 108 int i; 109 110 replptr = ALT_REPL_PTR(alt); 111 for (i = 0; i < nr_inst; i++) { 112 u32 insn; 113 114 insn = get_alt_insn(alt, origptr + i, replptr + i); 115 updptr[i] = cpu_to_le32(insn); 116 } 117 } 118 119 /* 120 * We provide our own, private D-cache cleaning function so that we don't 121 * accidentally call into the cache.S code, which is patched by us at 122 * runtime. 123 */ 124 static void clean_dcache_range_nopatch(u64 start, u64 end) 125 { 126 u64 cur, d_size, ctr_el0; 127 128 ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0); 129 d_size = 4 << cpuid_feature_extract_unsigned_field(ctr_el0, 130 CTR_EL0_DminLine_SHIFT); 131 cur = start & ~(d_size - 1); 132 do { 133 /* 134 * We must clean+invalidate to the PoC in order to avoid 135 * Cortex-A53 errata 826319, 827319, 824069 and 819472 136 * (this corresponds to ARM64_WORKAROUND_CLEAN_CACHE) 137 */ 138 asm volatile("dc civac, %0" : : "r" (cur) : "memory"); 139 } while (cur += d_size, cur < end); 140 } 141 142 static void __apply_alternatives(const struct alt_region *region, 143 bool is_module, 144 unsigned long *feature_mask) 145 { 146 struct alt_instr *alt; 147 __le32 *origptr, *updptr; 148 alternative_cb_t alt_cb; 149 150 for (alt = region->begin; alt < region->end; alt++) { 151 int nr_inst; 152 int cap = ALT_CAP(alt); 153 154 if (!test_bit(cap, feature_mask)) 155 continue; 156 157 if (!cpus_have_cap(cap)) 158 continue; 159 160 if (ALT_HAS_CB(alt)) 161 BUG_ON(alt->alt_len != 0); 162 else 163 BUG_ON(alt->alt_len != alt->orig_len); 164 165 origptr = ALT_ORIG_PTR(alt); 166 updptr = is_module ? origptr : lm_alias(origptr); 167 nr_inst = alt->orig_len / AARCH64_INSN_SIZE; 168 169 if (ALT_HAS_CB(alt)) 170 alt_cb = ALT_REPL_PTR(alt); 171 else 172 alt_cb = patch_alternative; 173 174 alt_cb(alt, origptr, updptr, nr_inst); 175 176 if (!is_module) { 177 clean_dcache_range_nopatch((u64)origptr, 178 (u64)(origptr + nr_inst)); 179 } 180 } 181 182 /* 183 * The core module code takes care of cache maintenance in 184 * flush_module_icache(). 185 */ 186 if (!is_module) { 187 dsb(ish); 188 icache_inval_all_pou(); 189 isb(); 190 191 /* Ignore ARM64_CB bit from feature mask */ 192 bitmap_or(applied_alternatives, applied_alternatives, 193 feature_mask, ARM64_NCAPS); 194 bitmap_and(applied_alternatives, applied_alternatives, 195 cpu_hwcaps, ARM64_NCAPS); 196 } 197 } 198 199 void apply_alternatives_vdso(void) 200 { 201 struct alt_region region; 202 const struct elf64_hdr *hdr; 203 const struct elf64_shdr *shdr; 204 const struct elf64_shdr *alt; 205 DECLARE_BITMAP(all_capabilities, ARM64_NCAPS); 206 207 bitmap_fill(all_capabilities, ARM64_NCAPS); 208 209 hdr = (struct elf64_hdr *)vdso_start; 210 shdr = (void *)hdr + hdr->e_shoff; 211 alt = find_section(hdr, shdr, ".altinstructions"); 212 if (!alt) 213 return; 214 215 region = (struct alt_region){ 216 .begin = (void *)hdr + alt->sh_offset, 217 .end = (void *)hdr + alt->sh_offset + alt->sh_size, 218 }; 219 220 __apply_alternatives(®ion, false, &all_capabilities[0]); 221 } 222 223 static const struct alt_region kernel_alternatives = { 224 .begin = (struct alt_instr *)__alt_instructions, 225 .end = (struct alt_instr *)__alt_instructions_end, 226 }; 227 228 /* 229 * We might be patching the stop_machine state machine, so implement a 230 * really simple polling protocol here. 231 */ 232 static int __apply_alternatives_multi_stop(void *unused) 233 { 234 /* We always have a CPU 0 at this point (__init) */ 235 if (smp_processor_id()) { 236 while (!all_alternatives_applied) 237 cpu_relax(); 238 isb(); 239 } else { 240 DECLARE_BITMAP(remaining_capabilities, ARM64_NCAPS); 241 242 bitmap_complement(remaining_capabilities, boot_capabilities, 243 ARM64_NCAPS); 244 245 BUG_ON(all_alternatives_applied); 246 __apply_alternatives(&kernel_alternatives, false, 247 remaining_capabilities); 248 /* Barriers provided by the cache flushing */ 249 all_alternatives_applied = 1; 250 } 251 252 return 0; 253 } 254 255 void __init apply_alternatives_all(void) 256 { 257 pr_info("applying system-wide alternatives\n"); 258 259 apply_alternatives_vdso(); 260 /* better not try code patching on a live SMP system */ 261 stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask); 262 } 263 264 /* 265 * This is called very early in the boot process (directly after we run 266 * a feature detect on the boot CPU). No need to worry about other CPUs 267 * here. 268 */ 269 void __init apply_boot_alternatives(void) 270 { 271 /* If called on non-boot cpu things could go wrong */ 272 WARN_ON(smp_processor_id() != 0); 273 274 pr_info("applying boot alternatives\n"); 275 276 __apply_alternatives(&kernel_alternatives, false, 277 &boot_capabilities[0]); 278 } 279 280 #ifdef CONFIG_MODULES 281 void apply_alternatives_module(void *start, size_t length) 282 { 283 struct alt_region region = { 284 .begin = start, 285 .end = start + length, 286 }; 287 DECLARE_BITMAP(all_capabilities, ARM64_NCAPS); 288 289 bitmap_fill(all_capabilities, ARM64_NCAPS); 290 291 __apply_alternatives(®ion, true, &all_capabilities[0]); 292 } 293 #endif 294 295 noinstr void alt_cb_patch_nops(struct alt_instr *alt, __le32 *origptr, 296 __le32 *updptr, int nr_inst) 297 { 298 for (int i = 0; i < nr_inst; i++) 299 updptr[i] = cpu_to_le32(aarch64_insn_gen_nop()); 300 } 301 EXPORT_SYMBOL(alt_cb_patch_nops); 302