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         size_t len;
  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                                          offset_in_page(addr));
  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         bool across_pages = (offset_in_page(addr) + len) > PAGE_SIZE;
  69         void *waddr = addr;
  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         preempt_disable();
  84
  85         if (across_pages)
  86                 patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
  87
  88         waddr = patch_map(addr, FIX_TEXT_POKE0);
  89
  90         memset(waddr, c, len);
  91
  92         /*
  93          * We could have just patched a function that is about to be
  94          * called so make sure we don't execute partially patched
  95          * instructions by flushing the icache as soon as possible.
  96          */
  97         local_flush_icache_range((unsigned long)waddr,
  98                                  (unsigned long)waddr + len);
  99
 100         patch_unmap(FIX_TEXT_POKE0);
 101
 102         if (across_pages)
 103                 patch_unmap(FIX_TEXT_POKE1);
 104
 105         preempt_enable();
 106
 107         return 0;
 108 }
 109 NOKPROBE_SYMBOL(__patch_insn_set);
 110
 111 static int __patch_insn_write(void *addr, const void *insn, size_t len)
 112 {
 113         bool across_pages = (offset_in_page(addr) + len) > PAGE_SIZE;
 114         void *waddr = addr;
 115         int ret;
 116
 117         /*
 118          * Only two pages can be mapped at a time for writing.
 119          */
 120         if (len + offset_in_page(addr) > 2 * PAGE_SIZE)
 121                 return -EINVAL;
 122
 123         /*
 124          * Before reaching here, it was expected to lock the text_mutex
 125          * already, so we don't need to give another lock here and could
 126          * ensure that it was safe between each cores.
 127          *
 128          * We're currently using stop_machine() for ftrace & kprobes, and while
 129          * that ensures text_mutex is held before installing the mappings it
 130          * does not ensure text_mutex is held by the calling thread.  That's
 131          * safe but triggers a lockdep failure, so just elide it for that
 132          * specific case.
 133          */
 134         if (!riscv_patch_in_stop_machine)
 135                 lockdep_assert_held(&text_mutex);
 136
 137         preempt_disable();
 138
 139         if (across_pages)
 140                 patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
 141
 142         waddr = patch_map(addr, FIX_TEXT_POKE0);
 143
 144         ret = copy_to_kernel_nofault(waddr, insn, len);
 145
 146         /*
 147          * We could have just patched a function that is about to be
 148          * called so make sure we don't execute partially patched
 149          * instructions by flushing the icache as soon as possible.
 150          */
 151         local_flush_icache_range((unsigned long)waddr,
 152                                  (unsigned long)waddr + len);
 153
 154         patch_unmap(FIX_TEXT_POKE0);
 155
 156         if (across_pages)
 157                 patch_unmap(FIX_TEXT_POKE1);
 158
 159         preempt_enable();
 160
 161         return ret;
 162 }
 163 NOKPROBE_SYMBOL(__patch_insn_write);
 164 #else
 165 static int __patch_insn_set(void *addr, u8 c, size_t len)
 166 {
 167         memset(addr, c, len);
 168
 169         return 0;
 170 }
 171 NOKPROBE_SYMBOL(__patch_insn_set);
 172
 173 static int __patch_insn_write(void *addr, const void *insn, size_t len)
 174 {
 175         return copy_to_kernel_nofault(addr, insn, len);
 176 }
 177 NOKPROBE_SYMBOL(__patch_insn_write);
 178 #endif /* CONFIG_MMU */
 179
 180 static int patch_insn_set(void *addr, u8 c, size_t len)
 181 {
 182         size_t size;
 183         int ret;
 184
 185         /*
 186          * __patch_insn_set() can only work on 2 pages at a time so call it in a
 187          * loop with len <= 2 * PAGE_SIZE.
 188          */
 189         while (len) {
 190                 size = min(len, PAGE_SIZE * 2 - offset_in_page(addr));
 191                 ret = __patch_insn_set(addr, c, size);
 192                 if (ret)
 193                         return ret;
 194
 195                 addr += size;
 196                 len -= size;
 197         }
 198
 199         return 0;
 200 }
 201 NOKPROBE_SYMBOL(patch_insn_set);
 202
 203 int patch_text_set_nosync(void *addr, u8 c, size_t len)
 204 {
 205         int ret;
 206
 207         ret = patch_insn_set(addr, c, len);
 208         if (!ret)
 209                 flush_icache_range((uintptr_t)addr, (uintptr_t)addr + len);
 210
 211         return ret;
 212 }
 213 NOKPROBE_SYMBOL(patch_text_set_nosync);
 214
 215 int patch_insn_write(void *addr, const void *insn, size_t len)
 216 {
 217         size_t size;
 218         int ret;
 219
 220         /*
 221          * Copy the instructions to the destination address, two pages at a time
 222          * because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
 223          */
 224         while (len) {
 225                 size = min(len, PAGE_SIZE * 2 - offset_in_page(addr));
 226                 ret = __patch_insn_write(addr, insn, size);
 227                 if (ret)
 228                         return ret;
 229
 230                 addr += size;
 231                 insn += size;
 232                 len -= size;
 233         }
 234
 235         return 0;
 236 }
 237 NOKPROBE_SYMBOL(patch_insn_write);
 238
 239 int patch_text_nosync(void *addr, const void *insns, size_t len)
 240 {
 241         int ret;
 242
 243         ret = patch_insn_write(addr, insns, len);
 244         if (!ret)
 245                 flush_icache_range((uintptr_t)addr, (uintptr_t)addr + len);
 246
 247         return ret;
 248 }
 249 NOKPROBE_SYMBOL(patch_text_nosync);
 250
 251 static int patch_text_cb(void *data)
 252 {
 253         struct patch_insn *patch = data;
 254         int ret = 0;
 255
 256         if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
 257                 ret = patch_insn_write(patch->addr, patch->insns, patch->len);
 258                 /*
 259                  * Make sure the patching store is effective *before* we
 260                  * increment the counter which releases all waiting CPUs
 261                  * by using the release variant of atomic increment. The
 262                  * release pairs with the call to local_flush_icache_all()
 263                  * on the waiting CPU.
 264                  */
 265                 atomic_inc_return_release(&patch->cpu_count);
 266         } else {
 267                 while (atomic_read(&patch->cpu_count) <= num_online_cpus())
 268                         cpu_relax();
 269
 270                 local_flush_icache_all();
 271         }
 272
 273         return ret;
 274 }
 275 NOKPROBE_SYMBOL(patch_text_cb);
 276
 277 int patch_text(void *addr, u32 *insns, size_t len)
 278 {
 279         int ret;
 280         struct patch_insn patch = {
 281                 .addr = addr,
 282                 .insns = insns,
 283                 .len = len,
 284                 .cpu_count = ATOMIC_INIT(0),
 285         };
 286
 287         /*
 288          * kprobes takes text_mutex, before calling patch_text(), but as we call
 289          * calls stop_machine(), the lockdep assertion in patch_insn_write()
 290          * gets confused by the context in which the lock is taken.
 291          * Instead, ensure the lock is held before calling stop_machine(), and
 292          * set riscv_patch_in_stop_machine to skip the check in
 293          * patch_insn_write().
 294          */
 295         lockdep_assert_held(&text_mutex);
 296         riscv_patch_in_stop_machine = true;
 297         ret = stop_machine_cpuslocked(patch_text_cb, &patch, cpu_online_mask);
 298         riscv_patch_in_stop_machine = false;
 299         return ret;
 300 }
 301 NOKPROBE_SYMBOL(patch_text);