1 /* 2 * alternative runtime patching 3 * inspired by the x86 version 4 * 5 * Copyright (C) 2014 ARM Ltd. 6 * 7 * This program is free software; you can redistribute it and/or modify 8 * it under the terms of the GNU General Public License version 2 as 9 * published by the Free Software Foundation. 10 * 11 * This program is distributed in the hope that it will be useful, 12 * but WITHOUT ANY WARRANTY; without even the implied warranty of 13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 * GNU General Public License for more details. 15 * 16 * You should have received a copy of the GNU General Public License 17 * along with this program. If not, see <http://www.gnu.org/licenses/>. 18 */ 19 20 #define pr_fmt(fmt) "alternatives: " fmt 21 22 #include <linux/init.h> 23 #include <linux/cpu.h> 24 #include <asm/cacheflush.h> 25 #include <asm/alternative.h> 26 #include <asm/cpufeature.h> 27 #include <asm/insn.h> 28 #include <asm/sections.h> 29 #include <linux/stop_machine.h> 30 31 #define __ALT_PTR(a,f) ((void *)&(a)->f + (a)->f) 32 #define ALT_ORIG_PTR(a) __ALT_PTR(a, orig_offset) 33 #define ALT_REPL_PTR(a) __ALT_PTR(a, alt_offset) 34 35 int alternatives_applied; 36 37 struct alt_region { 38 struct alt_instr *begin; 39 struct alt_instr *end; 40 }; 41 42 /* 43 * Check if the target PC is within an alternative block. 44 */ 45 static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc) 46 { 47 unsigned long replptr; 48 49 if (kernel_text_address(pc)) 50 return 1; 51 52 replptr = (unsigned long)ALT_REPL_PTR(alt); 53 if (pc >= replptr && pc <= (replptr + alt->alt_len)) 54 return 0; 55 56 /* 57 * Branching into *another* alternate sequence is doomed, and 58 * we're not even trying to fix it up. 59 */ 60 BUG(); 61 } 62 63 #define align_down(x, a) ((unsigned long)(x) & ~(((unsigned long)(a)) - 1)) 64 65 static u32 get_alt_insn(struct alt_instr *alt, __le32 *insnptr, __le32 *altinsnptr) 66 { 67 u32 insn; 68 69 insn = le32_to_cpu(*altinsnptr); 70 71 if (aarch64_insn_is_branch_imm(insn)) { 72 s32 offset = aarch64_get_branch_offset(insn); 73 unsigned long target; 74 75 target = (unsigned long)altinsnptr + offset; 76 77 /* 78 * If we're branching inside the alternate sequence, 79 * do not rewrite the instruction, as it is already 80 * correct. Otherwise, generate the new instruction. 81 */ 82 if (branch_insn_requires_update(alt, target)) { 83 offset = target - (unsigned long)insnptr; 84 insn = aarch64_set_branch_offset(insn, offset); 85 } 86 } else if (aarch64_insn_is_adrp(insn)) { 87 s32 orig_offset, new_offset; 88 unsigned long target; 89 90 /* 91 * If we're replacing an adrp instruction, which uses PC-relative 92 * immediate addressing, adjust the offset to reflect the new 93 * PC. adrp operates on 4K aligned addresses. 94 */ 95 orig_offset = aarch64_insn_adrp_get_offset(insn); 96 target = align_down(altinsnptr, SZ_4K) + orig_offset; 97 new_offset = target - align_down(insnptr, SZ_4K); 98 insn = aarch64_insn_adrp_set_offset(insn, new_offset); 99 } else if (aarch64_insn_uses_literal(insn)) { 100 /* 101 * Disallow patching unhandled instructions using PC relative 102 * literal addresses 103 */ 104 BUG(); 105 } 106 107 return insn; 108 } 109 110 static void patch_alternative(struct alt_instr *alt, 111 __le32 *origptr, __le32 *updptr, int nr_inst) 112 { 113 __le32 *replptr; 114 int i; 115 116 replptr = ALT_REPL_PTR(alt); 117 for (i = 0; i < nr_inst; i++) { 118 u32 insn; 119 120 insn = get_alt_insn(alt, origptr + i, replptr + i); 121 updptr[i] = cpu_to_le32(insn); 122 } 123 } 124 125 static void __apply_alternatives(void *alt_region, bool use_linear_alias) 126 { 127 struct alt_instr *alt; 128 struct alt_region *region = alt_region; 129 __le32 *origptr, *updptr; 130 alternative_cb_t alt_cb; 131 132 for (alt = region->begin; alt < region->end; alt++) { 133 int nr_inst; 134 135 /* Use ARM64_CB_PATCH as an unconditional patch */ 136 if (alt->cpufeature < ARM64_CB_PATCH && 137 !cpus_have_cap(alt->cpufeature)) 138 continue; 139 140 if (alt->cpufeature == ARM64_CB_PATCH) 141 BUG_ON(alt->alt_len != 0); 142 else 143 BUG_ON(alt->alt_len != alt->orig_len); 144 145 pr_info_once("patching kernel code\n"); 146 147 origptr = ALT_ORIG_PTR(alt); 148 updptr = use_linear_alias ? lm_alias(origptr) : origptr; 149 nr_inst = alt->orig_len / AARCH64_INSN_SIZE; 150 151 if (alt->cpufeature < ARM64_CB_PATCH) 152 alt_cb = patch_alternative; 153 else 154 alt_cb = ALT_REPL_PTR(alt); 155 156 alt_cb(alt, origptr, updptr, nr_inst); 157 158 flush_icache_range((uintptr_t)origptr, 159 (uintptr_t)(origptr + nr_inst)); 160 } 161 } 162 163 /* 164 * We might be patching the stop_machine state machine, so implement a 165 * really simple polling protocol here. 166 */ 167 static int __apply_alternatives_multi_stop(void *unused) 168 { 169 struct alt_region region = { 170 .begin = (struct alt_instr *)__alt_instructions, 171 .end = (struct alt_instr *)__alt_instructions_end, 172 }; 173 174 /* We always have a CPU 0 at this point (__init) */ 175 if (smp_processor_id()) { 176 while (!READ_ONCE(alternatives_applied)) 177 cpu_relax(); 178 isb(); 179 } else { 180 BUG_ON(alternatives_applied); 181 __apply_alternatives(®ion, true); 182 /* Barriers provided by the cache flushing */ 183 WRITE_ONCE(alternatives_applied, 1); 184 } 185 186 return 0; 187 } 188 189 void __init apply_alternatives_all(void) 190 { 191 /* better not try code patching on a live SMP system */ 192 stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask); 193 } 194 195 void apply_alternatives(void *start, size_t length) 196 { 197 struct alt_region region = { 198 .begin = start, 199 .end = start + length, 200 }; 201 202 __apply_alternatives(®ion, false); 203 } 204