arch/riscv/kernel/patch.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (C) 2020 SiFive
   4  */
   5
   6 #include <linux/spinlock.h>
   7 #include <linux/mm.h>
   8 #include <linux/memory.h>
   9 #include <linux/string.h>
  10 #include <linux/uaccess.h>
  11 #include <linux/stop_machine.h>
  12 #include <asm/kprobes.h>
  13 #include <asm/cacheflush.h>
  14 #include <asm/fixmap.h>
  15 #include <asm/ftrace.h>
  16 #include <asm/patch.h>
  17 #include <asm/sections.h>
  18
  19 struct patch_insn {
  20         void *addr;
  21         u32 *insns;
  22         int ninsns;
  23         atomic_t cpu_count;
  24 };
  25
  26 int riscv_patch_in_stop_machine = false;
  27
  28 #ifdef CONFIG_MMU
  29
  30 static inline bool is_kernel_exittext(uintptr_t addr)
  31 {
  32         return system_state < SYSTEM_RUNNING &&
  33                 addr >= (uintptr_t)__exittext_begin &&
  34                 addr < (uintptr_t)__exittext_end;
  35 }
  36
  37 /*
  38  * The fix_to_virt(, idx) needs a const value (not a dynamic variable of
  39  * reg-a0) or BUILD_BUG_ON failed with "idx >= __end_of_fixed_addresses".
  40  * So use '__always_inline' and 'const unsigned int fixmap' here.
  41  */
  42 static __always_inline void *patch_map(void *addr, const unsigned int fixmap)
  43 {
  44         uintptr_t uintaddr = (uintptr_t) addr;
  45         struct page *page;
  46
  47         if (core_kernel_text(uintaddr) || is_kernel_exittext(uintaddr))
  48                 page = phys_to_page(__pa_symbol(addr));
  49         else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
  50                 page = vmalloc_to_page(addr);
  51         else
  52                 return addr;
  53
  54         BUG_ON(!page);
  55
  56         return (void *)set_fixmap_offset(fixmap, page_to_phys(page) +
  57                                          (uintaddr & ~PAGE_MASK));
  58 }
  59
  60 static void patch_unmap(int fixmap)
  61 {
  62         clear_fixmap(fixmap);
  63 }
  64 NOKPROBE_SYMBOL(patch_unmap);
  65
  66 static int __patch_insn_set(void *addr, u8 c, size_t len)
  67 {
  68         void *waddr = addr;
  69         bool across_pages = (((uintptr_t)addr & ~PAGE_MASK) + len) > PAGE_SIZE;
  70
  71         /*
  72          * Only two pages can be mapped at a time for writing.
  73          */
  74         if (len + offset_in_page(addr) > 2 * PAGE_SIZE)
  75                 return -EINVAL;
  76         /*
  77          * Before reaching here, it was expected to lock the text_mutex
  78          * already, so we don't need to give another lock here and could
  79          * ensure that it was safe between each cores.
  80          */
  81         lockdep_assert_held(&text_mutex);
  82
  83         if (across_pages)
  84                 patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
  85
  86         waddr = patch_map(addr, FIX_TEXT_POKE0);
  87
  88         memset(waddr, c, len);
  89
  90         patch_unmap(FIX_TEXT_POKE0);
  91
  92         if (across_pages)
  93                 patch_unmap(FIX_TEXT_POKE1);
  94
  95         return 0;
  96 }
  97 NOKPROBE_SYMBOL(__patch_insn_set);
  98
  99 static int __patch_insn_write(void *addr, const void *insn, size_t len)
 100 {
 101         void *waddr = addr;
 102         bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
 103         int ret;
 104
 105         /*
 106          * Only two pages can be mapped at a time for writing.
 107          */
 108         if (len + offset_in_page(addr) > 2 * PAGE_SIZE)
 109                 return -EINVAL;
 110
 111         /*
 112          * Before reaching here, it was expected to lock the text_mutex
 113          * already, so we don't need to give another lock here and could
 114          * ensure that it was safe between each cores.
 115          *
 116          * We're currently using stop_machine() for ftrace & kprobes, and while
 117          * that ensures text_mutex is held before installing the mappings it
 118          * does not ensure text_mutex is held by the calling thread.  That's
 119          * safe but triggers a lockdep failure, so just elide it for that
 120          * specific case.
 121          */
 122         if (!riscv_patch_in_stop_machine)
 123                 lockdep_assert_held(&text_mutex);
 124
 125         if (across_pages)
 126                 patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
 127
 128         waddr = patch_map(addr, FIX_TEXT_POKE0);
 129
 130         ret = copy_to_kernel_nofault(waddr, insn, len);
 131
 132         patch_unmap(FIX_TEXT_POKE0);
 133
 134         if (across_pages)
 135                 patch_unmap(FIX_TEXT_POKE1);
 136
 137         return ret;
 138 }
 139 NOKPROBE_SYMBOL(__patch_insn_write);
 140 #else
 141 static int __patch_insn_set(void *addr, u8 c, size_t len)
 142 {
 143         memset(addr, c, len);
 144
 145         return 0;
 146 }
 147 NOKPROBE_SYMBOL(__patch_insn_set);
 148
 149 static int __patch_insn_write(void *addr, const void *insn, size_t len)
 150 {
 151         return copy_to_kernel_nofault(addr, insn, len);
 152 }
 153 NOKPROBE_SYMBOL(__patch_insn_write);
 154 #endif /* CONFIG_MMU */
 155
 156 static int patch_insn_set(void *addr, u8 c, size_t len)
 157 {
 158         size_t patched = 0;
 159         size_t size;
 160         int ret = 0;
 161
 162         /*
 163          * __patch_insn_set() can only work on 2 pages at a time so call it in a
 164          * loop with len <= 2 * PAGE_SIZE.
 165          */
 166         while (patched < len && !ret) {
 167                 size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
 168                 ret = __patch_insn_set(addr + patched, c, size);
 169
 170                 patched += size;
 171         }
 172
 173         return ret;
 174 }
 175 NOKPROBE_SYMBOL(patch_insn_set);
 176
 177 int patch_text_set_nosync(void *addr, u8 c, size_t len)
 178 {
 179         u32 *tp = addr;
 180         int ret;
 181
 182         ret = patch_insn_set(tp, c, len);
 183
 184         if (!ret)
 185                 flush_icache_range((uintptr_t)tp, (uintptr_t)tp + len);
 186
 187         return ret;
 188 }
 189 NOKPROBE_SYMBOL(patch_text_set_nosync);
 190
 191 static int patch_insn_write(void *addr, const void *insn, size_t len)
 192 {
 193         size_t patched = 0;
 194         size_t size;
 195         int ret = 0;
 196
 197         /*
 198          * Copy the instructions to the destination address, two pages at a time
 199          * because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
 200          */
 201         while (patched < len && !ret) {
 202                 size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
 203                 ret = __patch_insn_write(addr + patched, insn + patched, size);
 204
 205                 patched += size;
 206         }
 207
 208         return ret;
 209 }
 210 NOKPROBE_SYMBOL(patch_insn_write);
 211
 212 int patch_text_nosync(void *addr, const void *insns, size_t len)
 213 {
 214         u32 *tp = addr;
 215         int ret;
 216
 217         ret = patch_insn_write(tp, insns, len);
 218
 219         if (!ret)
 220                 flush_icache_range((uintptr_t) tp, (uintptr_t) tp + len);
 221
 222         return ret;
 223 }
 224 NOKPROBE_SYMBOL(patch_text_nosync);
 225
 226 static int patch_text_cb(void *data)
 227 {
 228         struct patch_insn *patch = data;
 229         unsigned long len;
 230         int i, ret = 0;
 231
 232         if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
 233                 for (i = 0; ret == 0 && i < patch->ninsns; i++) {
 234                         len = GET_INSN_LENGTH(patch->insns[i]);
 235                         ret = patch_text_nosync(patch->addr + i * len,
 236                                                 &patch->insns[i], len);
 237                 }
 238                 atomic_inc(&patch->cpu_count);
 239         } else {
 240                 while (atomic_read(&patch->cpu_count) <= num_online_cpus())
 241                         cpu_relax();
 242                 smp_mb();
 243         }
 244
 245         return ret;
 246 }
 247 NOKPROBE_SYMBOL(patch_text_cb);
 248
 249 int patch_text(void *addr, u32 *insns, int ninsns)
 250 {
 251         int ret;
 252         struct patch_insn patch = {
 253                 .addr = addr,
 254                 .insns = insns,
 255                 .ninsns = ninsns,
 256                 .cpu_count = ATOMIC_INIT(0),
 257         };
 258
 259         /*
 260          * kprobes takes text_mutex, before calling patch_text(), but as we call
 261          * calls stop_machine(), the lockdep assertion in patch_insn_write()
 262          * gets confused by the context in which the lock is taken.
 263          * Instead, ensure the lock is held before calling stop_machine(), and
 264          * set riscv_patch_in_stop_machine to skip the check in
 265          * patch_insn_write().
 266          */
 267         lockdep_assert_held(&text_mutex);
 268         riscv_patch_in_stop_machine = true;
 269         ret = stop_machine_cpuslocked(patch_text_cb, &patch, cpu_online_mask);
 270         riscv_patch_in_stop_machine = false;
 271         return ret;
 272 }
 273 NOKPROBE_SYMBOL(patch_text);