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/uaccess.h>
  10 #include <linux/stop_machine.h>
  11 #include <asm/kprobes.h>
  12 #include <asm/cacheflush.h>
  13 #include <asm/fixmap.h>
  14 #include <asm/ftrace.h>
  15 #include <asm/patch.h>
  16 #include <asm/sections.h>
  17
  18 struct patch_insn {
  19         void *addr;
  20         u32 insn;
  21         atomic_t cpu_count;
  22 };
  23
  24 int riscv_patch_in_stop_machine = false;
  25
  26 #ifdef CONFIG_MMU
  27
  28 static inline bool is_kernel_exittext(uintptr_t addr)
  29 {
  30         return system_state < SYSTEM_RUNNING &&
  31                 addr >= (uintptr_t)__exittext_begin &&
  32                 addr < (uintptr_t)__exittext_end;
  33 }
  34
  35 /*
  36  * The fix_to_virt(, idx) needs a const value (not a dynamic variable of
  37  * reg-a0) or BUILD_BUG_ON failed with "idx >= __end_of_fixed_addresses".
  38  * So use '__always_inline' and 'const unsigned int fixmap' here.
  39  */
  40 static __always_inline void *patch_map(void *addr, const unsigned int fixmap)
  41 {
  42         uintptr_t uintaddr = (uintptr_t) addr;
  43         struct page *page;
  44
  45         if (core_kernel_text(uintaddr) || is_kernel_exittext(uintaddr))
  46                 page = phys_to_page(__pa_symbol(addr));
  47         else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
  48                 page = vmalloc_to_page(addr);
  49         else
  50                 return addr;
  51
  52         BUG_ON(!page);
  53
  54         return (void *)set_fixmap_offset(fixmap, page_to_phys(page) +
  55                                          (uintaddr & ~PAGE_MASK));
  56 }
  57
  58 static void patch_unmap(int fixmap)
  59 {
  60         clear_fixmap(fixmap);
  61 }
  62 NOKPROBE_SYMBOL(patch_unmap);
  63
  64 static int patch_insn_write(void *addr, const void *insn, size_t len)
  65 {
  66         void *waddr = addr;
  67         bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
  68         int ret;
  69
  70         /*
  71          * Before reaching here, it was expected to lock the text_mutex
  72          * already, so we don't need to give another lock here and could
  73          * ensure that it was safe between each cores.
  74          *
  75          * We're currently using stop_machine() for ftrace & kprobes, and while
  76          * that ensures text_mutex is held before installing the mappings it
  77          * does not ensure text_mutex is held by the calling thread.  That's
  78          * safe but triggers a lockdep failure, so just elide it for that
  79          * specific case.
  80          */
  81         if (!riscv_patch_in_stop_machine)
  82                 lockdep_assert_held(&text_mutex);
  83
  84         if (across_pages)
  85                 patch_map(addr + len, FIX_TEXT_POKE1);
  86
  87         waddr = patch_map(addr, FIX_TEXT_POKE0);
  88
  89         ret = copy_to_kernel_nofault(waddr, insn, len);
  90
  91         patch_unmap(FIX_TEXT_POKE0);
  92
  93         if (across_pages)
  94                 patch_unmap(FIX_TEXT_POKE1);
  95
  96         return ret;
  97 }
  98 NOKPROBE_SYMBOL(patch_insn_write);
  99 #else
 100 static int patch_insn_write(void *addr, const void *insn, size_t len)
 101 {
 102         return copy_to_kernel_nofault(addr, insn, len);
 103 }
 104 NOKPROBE_SYMBOL(patch_insn_write);
 105 #endif /* CONFIG_MMU */
 106
 107 int patch_text_nosync(void *addr, const void *insns, size_t len)
 108 {
 109         u32 *tp = addr;
 110         int ret;
 111
 112         ret = patch_insn_write(tp, insns, len);
 113
 114         if (!ret)
 115                 flush_icache_range((uintptr_t) tp, (uintptr_t) tp + len);
 116
 117         return ret;
 118 }
 119 NOKPROBE_SYMBOL(patch_text_nosync);
 120
 121 static int patch_text_cb(void *data)
 122 {
 123         struct patch_insn *patch = data;
 124         int ret = 0;
 125
 126         if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
 127                 ret =
 128                     patch_text_nosync(patch->addr, &patch->insn,
 129                                             GET_INSN_LENGTH(patch->insn));
 130                 atomic_inc(&patch->cpu_count);
 131         } else {
 132                 while (atomic_read(&patch->cpu_count) <= num_online_cpus())
 133                         cpu_relax();
 134                 smp_mb();
 135         }
 136
 137         return ret;
 138 }
 139 NOKPROBE_SYMBOL(patch_text_cb);
 140
 141 int patch_text(void *addr, u32 insn)
 142 {
 143         int ret;
 144         struct patch_insn patch = {
 145                 .addr = addr,
 146                 .insn = insn,
 147                 .cpu_count = ATOMIC_INIT(0),
 148         };
 149
 150         /*
 151          * kprobes takes text_mutex, before calling patch_text(), but as we call
 152          * calls stop_machine(), the lockdep assertion in patch_insn_write()
 153          * gets confused by the context in which the lock is taken.
 154          * Instead, ensure the lock is held before calling stop_machine(), and
 155          * set riscv_patch_in_stop_machine to skip the check in
 156          * patch_insn_write().
 157          */
 158         lockdep_assert_held(&text_mutex);
 159         riscv_patch_in_stop_machine = true;
 160         ret = stop_machine_cpuslocked(patch_text_cb, &patch, cpu_online_mask);
 161         riscv_patch_in_stop_machine = false;
 162         return ret;
 163 }
 164 NOKPROBE_SYMBOL(patch_text);