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