root/arch/arm64/kernel/alternative.c

DEFINITIONS

1. alternative_is_applied
2. branch_insn_requires_update
3. get_alt_insn
4. patch_alternative
5. clean_dcache_range_nopatch
6. __apply_alternatives
7. __apply_alternatives_multi_stop
8. apply_alternatives_all
9. apply_boot_alternatives
10. apply_alternatives_module

   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 <asm/cacheflush.h>
  14 #include <asm/alternative.h>
  15 #include <asm/cpufeature.h>
  16 #include <asm/insn.h>
  17 #include <asm/sections.h>
  18 #include <linux/stop_machine.h>
  19 
  20 #define __ALT_PTR(a,f)          ((void *)&(a)->f + (a)->f)
  21 #define ALT_ORIG_PTR(a)         __ALT_PTR(a, orig_offset)
  22 #define ALT_REPL_PTR(a)         __ALT_PTR(a, alt_offset)
  23 
  24 static int all_alternatives_applied;
  25 
  26 static DECLARE_BITMAP(applied_alternatives, ARM64_NCAPS);
  27 
  28 struct alt_region {
  29         struct alt_instr *begin;
  30         struct alt_instr *end;
  31 };
  32 
  33 bool alternative_is_applied(u16 cpufeature)
  34 {
  35         if (WARN_ON(cpufeature >= ARM64_NCAPS))
  36                 return false;
  37 
  38         return test_bit(cpufeature, applied_alternatives);
  39 }
  40 
  41 /*
  42  * Check if the target PC is within an alternative block.
  43  */
  44 static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc)
  45 {
  46         unsigned long replptr;
  47 
  48         if (kernel_text_address(pc))
  49                 return true;
  50 
  51         replptr = (unsigned long)ALT_REPL_PTR(alt);
  52         if (pc >= replptr && pc <= (replptr + alt->alt_len))
  53                 return false;
  54 
  55         /*
  56          * Branching into *another* alternate sequence is doomed, and
  57          * we're not even trying to fix it up.
  58          */
  59         BUG();
  60 }
  61 
  62 #define align_down(x, a)        ((unsigned long)(x) & ~(((unsigned long)(a)) - 1))
  63 
  64 static u32 get_alt_insn(struct alt_instr *alt, __le32 *insnptr, __le32 *altinsnptr)
  65 {
  66         u32 insn;
  67 
  68         insn = le32_to_cpu(*altinsnptr);
  69 
  70         if (aarch64_insn_is_branch_imm(insn)) {
  71                 s32 offset = aarch64_get_branch_offset(insn);
  72                 unsigned long target;
  73 
  74                 target = (unsigned long)altinsnptr + offset;
  75 
  76                 /*
  77                  * If we're branching inside the alternate sequence,
  78                  * do not rewrite the instruction, as it is already
  79                  * correct. Otherwise, generate the new instruction.
  80                  */
  81                 if (branch_insn_requires_update(alt, target)) {
  82                         offset = target - (unsigned long)insnptr;
  83                         insn = aarch64_set_branch_offset(insn, offset);
  84                 }
  85         } else if (aarch64_insn_is_adrp(insn)) {
  86                 s32 orig_offset, new_offset;
  87                 unsigned long target;
  88 
  89                 /*
  90                  * If we're replacing an adrp instruction, which uses PC-relative
  91                  * immediate addressing, adjust the offset to reflect the new
  92                  * PC. adrp operates on 4K aligned addresses.
  93                  */
  94                 orig_offset  = aarch64_insn_adrp_get_offset(insn);
  95                 target = align_down(altinsnptr, SZ_4K) + orig_offset;
  96                 new_offset = target - align_down(insnptr, SZ_4K);
  97                 insn = aarch64_insn_adrp_set_offset(insn, new_offset);
  98         } else if (aarch64_insn_uses_literal(insn)) {
  99                 /*
 100                  * Disallow patching unhandled instructions using PC relative
 101                  * literal addresses
 102                  */
 103                 BUG();
 104         }
 105 
 106         return insn;
 107 }
 108 
 109 static void patch_alternative(struct alt_instr *alt,
 110                               __le32 *origptr, __le32 *updptr, int nr_inst)
 111 {
 112         __le32 *replptr;
 113         int i;
 114 
 115         replptr = ALT_REPL_PTR(alt);
 116         for (i = 0; i < nr_inst; i++) {
 117                 u32 insn;
 118 
 119                 insn = get_alt_insn(alt, origptr + i, replptr + i);
 120                 updptr[i] = cpu_to_le32(insn);
 121         }
 122 }
 123 
 124 /*
 125  * We provide our own, private D-cache cleaning function so that we don't
 126  * accidentally call into the cache.S code, which is patched by us at
 127  * runtime.
 128  */
 129 static void clean_dcache_range_nopatch(u64 start, u64 end)
 130 {
 131         u64 cur, d_size, ctr_el0;
 132 
 133         ctr_el0 = read_sanitised_ftr_reg(SYS_CTR_EL0);
 134         d_size = 4 << cpuid_feature_extract_unsigned_field(ctr_el0,
 135                                                            CTR_DMINLINE_SHIFT);
 136         cur = start & ~(d_size - 1);
 137         do {
 138                 /*
 139                  * We must clean+invalidate to the PoC in order to avoid
 140                  * Cortex-A53 errata 826319, 827319, 824069 and 819472
 141                  * (this corresponds to ARM64_WORKAROUND_CLEAN_CACHE)
 142                  */
 143                 asm volatile("dc civac, %0" : : "r" (cur) : "memory");
 144         } while (cur += d_size, cur < end);
 145 }
 146 
 147 static void __apply_alternatives(void *alt_region,  bool is_module,
 148                                  unsigned long *feature_mask)
 149 {
 150         struct alt_instr *alt;
 151         struct alt_region *region = alt_region;
 152         __le32 *origptr, *updptr;
 153         alternative_cb_t alt_cb;
 154 
 155         for (alt = region->begin; alt < region->end; alt++) {
 156                 int nr_inst;
 157 
 158                 if (!test_bit(alt->cpufeature, feature_mask))
 159                         continue;
 160 
 161                 /* Use ARM64_CB_PATCH as an unconditional patch */
 162                 if (alt->cpufeature < ARM64_CB_PATCH &&
 163                     !cpus_have_cap(alt->cpufeature))
 164                         continue;
 165 
 166                 if (alt->cpufeature == ARM64_CB_PATCH)
 167                         BUG_ON(alt->alt_len != 0);
 168                 else
 169                         BUG_ON(alt->alt_len != alt->orig_len);
 170 
 171                 pr_info_once("patching kernel code\n");
 172 
 173                 origptr = ALT_ORIG_PTR(alt);
 174                 updptr = is_module ? origptr : lm_alias(origptr);
 175                 nr_inst = alt->orig_len / AARCH64_INSN_SIZE;
 176 
 177                 if (alt->cpufeature < ARM64_CB_PATCH)
 178                         alt_cb = patch_alternative;
 179                 else
 180                         alt_cb  = ALT_REPL_PTR(alt);
 181 
 182                 alt_cb(alt, origptr, updptr, nr_inst);
 183 
 184                 if (!is_module) {
 185                         clean_dcache_range_nopatch((u64)origptr,
 186                                                    (u64)(origptr + nr_inst));
 187                 }
 188         }
 189 
 190         /*
 191          * The core module code takes care of cache maintenance in
 192          * flush_module_icache().
 193          */
 194         if (!is_module) {
 195                 dsb(ish);
 196                 __flush_icache_all();
 197                 isb();
 198 
 199                 /* Ignore ARM64_CB bit from feature mask */
 200                 bitmap_or(applied_alternatives, applied_alternatives,
 201                           feature_mask, ARM64_NCAPS);
 202                 bitmap_and(applied_alternatives, applied_alternatives,
 203                            cpu_hwcaps, ARM64_NCAPS);
 204         }
 205 }
 206 
 207 /*
 208  * We might be patching the stop_machine state machine, so implement a
 209  * really simple polling protocol here.
 210  */
 211 static int __apply_alternatives_multi_stop(void *unused)
 212 {
 213         struct alt_region region = {
 214                 .begin  = (struct alt_instr *)__alt_instructions,
 215                 .end    = (struct alt_instr *)__alt_instructions_end,
 216         };
 217 
 218         /* We always have a CPU 0 at this point (__init) */
 219         if (smp_processor_id()) {
 220                 while (!READ_ONCE(all_alternatives_applied))
 221                         cpu_relax();
 222                 isb();
 223         } else {
 224                 DECLARE_BITMAP(remaining_capabilities, ARM64_NPATCHABLE);
 225 
 226                 bitmap_complement(remaining_capabilities, boot_capabilities,
 227                                   ARM64_NPATCHABLE);
 228 
 229                 BUG_ON(all_alternatives_applied);
 230                 __apply_alternatives(&region, false, remaining_capabilities);
 231                 /* Barriers provided by the cache flushing */
 232                 WRITE_ONCE(all_alternatives_applied, 1);
 233         }
 234 
 235         return 0;
 236 }
 237 
 238 void __init apply_alternatives_all(void)
 239 {
 240         /* better not try code patching on a live SMP system */
 241         stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask);
 242 }
 243 
 244 /*
 245  * This is called very early in the boot process (directly after we run
 246  * a feature detect on the boot CPU). No need to worry about other CPUs
 247  * here.
 248  */
 249 void __init apply_boot_alternatives(void)
 250 {
 251         struct alt_region region = {
 252                 .begin  = (struct alt_instr *)__alt_instructions,
 253                 .end    = (struct alt_instr *)__alt_instructions_end,
 254         };
 255 
 256         /* If called on non-boot cpu things could go wrong */
 257         WARN_ON(smp_processor_id() != 0);
 258 
 259         __apply_alternatives(&region, false, &boot_capabilities[0]);
 260 }
 261 
 262 #ifdef CONFIG_MODULES
 263 void apply_alternatives_module(void *start, size_t length)
 264 {
 265         struct alt_region region = {
 266                 .begin  = start,
 267                 .end    = start + length,
 268         };
 269         DECLARE_BITMAP(all_capabilities, ARM64_NPATCHABLE);
 270 
 271         bitmap_fill(all_capabilities, ARM64_NPATCHABLE);
 272 
 273         __apply_alternatives(&region, true, &all_capabilities[0]);
 274 }
 275 #endif