arch/arm64/kernel/alternative.c

   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)          (u32 *)((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 struct alt_region {
  36         struct alt_instr *begin;
  37         struct alt_instr *end;
  38 };
  39
  40 /*
  41  * Check if the target PC is within an alternative block.
  42  */
  43 static bool branch_insn_requires_update(struct alt_instr *alt, unsigned long pc)
  44 {
  45         unsigned long replptr;
  46
  47         if (kernel_text_address(pc))
  48                 return 1;
  49
  50         replptr = (unsigned long)ALT_REPL_PTR(alt);
  51         if (pc >= replptr && pc <= (replptr + alt->alt_len))
  52                 return 0;
  53
  54         /*
  55          * Branching into *another* alternate sequence is doomed, and
  56          * we're not even trying to fix it up.
  57          */
  58         BUG();
  59 }
  60
  61 #define align_down(x, a)        ((unsigned long)(x) & ~(((unsigned long)(a)) - 1))
  62
  63 static u32 get_alt_insn(struct alt_instr *alt, u32 *insnptr, u32 *altinsnptr)
  64 {
  65         u32 insn;
  66
  67         insn = le32_to_cpu(*altinsnptr);
  68
  69         if (aarch64_insn_is_branch_imm(insn)) {
  70                 s32 offset = aarch64_get_branch_offset(insn);
  71                 unsigned long target;
  72
  73                 target = (unsigned long)altinsnptr + offset;
  74
  75                 /*
  76                  * If we're branching inside the alternate sequence,
  77                  * do not rewrite the instruction, as it is already
  78                  * correct. Otherwise, generate the new instruction.
  79                  */
  80                 if (branch_insn_requires_update(alt, target)) {
  81                         offset = target - (unsigned long)insnptr;
  82                         insn = aarch64_set_branch_offset(insn, offset);
  83                 }
  84         } else if (aarch64_insn_is_adrp(insn)) {
  85                 s32 orig_offset, new_offset;
  86                 unsigned long target;
  87
  88                 /*
  89                  * If we're replacing an adrp instruction, which uses PC-relative
  90                  * immediate addressing, adjust the offset to reflect the new
  91                  * PC. adrp operates on 4K aligned addresses.
  92                  */
  93                 orig_offset  = aarch64_insn_adrp_get_offset(insn);
  94                 target = align_down(altinsnptr, SZ_4K) + orig_offset;
  95                 new_offset = target - align_down(insnptr, SZ_4K);
  96                 insn = aarch64_insn_adrp_set_offset(insn, new_offset);
  97         } else if (aarch64_insn_uses_literal(insn)) {
  98                 /*
  99                  * Disallow patching unhandled instructions using PC relative
 100                  * literal addresses
 101                  */
 102                 BUG();
 103         }
 104
 105         return insn;
 106 }
 107
 108 static void __apply_alternatives(void *alt_region)
 109 {
 110         struct alt_instr *alt;
 111         struct alt_region *region = alt_region;
 112         u32 *origptr, *replptr;
 113
 114         for (alt = region->begin; alt < region->end; alt++) {
 115                 u32 insn;
 116                 int i, nr_inst;
 117
 118                 if (!cpus_have_cap(alt->cpufeature))
 119                         continue;
 120
 121                 BUG_ON(alt->alt_len != alt->orig_len);
 122
 123                 pr_info_once("patching kernel code\n");
 124
 125                 origptr = ALT_ORIG_PTR(alt);
 126                 replptr = ALT_REPL_PTR(alt);
 127                 nr_inst = alt->alt_len / sizeof(insn);
 128
 129                 for (i = 0; i < nr_inst; i++) {
 130                         insn = get_alt_insn(alt, origptr + i, replptr + i);
 131                         *(origptr + i) = cpu_to_le32(insn);
 132                 }
 133
 134                 flush_icache_range((uintptr_t)origptr,
 135                                    (uintptr_t)(origptr + nr_inst));
 136         }
 137 }
 138
 139 /*
 140  * We might be patching the stop_machine state machine, so implement a
 141  * really simple polling protocol here.
 142  */
 143 static int __apply_alternatives_multi_stop(void *unused)
 144 {
 145         static int patched = 0;
 146         struct alt_region region = {
 147                 .begin  = (struct alt_instr *)__alt_instructions,
 148                 .end    = (struct alt_instr *)__alt_instructions_end,
 149         };
 150
 151         /* We always have a CPU 0 at this point (__init) */
 152         if (smp_processor_id()) {
 153                 while (!READ_ONCE(patched))
 154                         cpu_relax();
 155                 isb();
 156         } else {
 157                 BUG_ON(patched);
 158                 __apply_alternatives(&region);
 159                 /* Barriers provided by the cache flushing */
 160                 WRITE_ONCE(patched, 1);
 161         }
 162
 163         return 0;
 164 }
 165
 166 void __init apply_alternatives_all(void)
 167 {
 168         /* better not try code patching on a live SMP system */
 169         stop_machine(__apply_alternatives_multi_stop, NULL, cpu_online_mask);
 170 }
 171
 172 void apply_alternatives(void *start, size_t length)
 173 {
 174         struct alt_region region = {
 175                 .begin  = start,
 176                 .end    = start + length,
 177         };
 178
 179         __apply_alternatives(&region);
 180 }