kernel/extable.c

   1 /* Rewritten by Rusty Russell, on the backs of many others...
   2    Copyright (C) 2001 Rusty Russell, 2002 Rusty Russell IBM.
   3
   4     This program is free software; you can redistribute it and/or modify
   5     it under the terms of the GNU General Public License as published by
   6     the Free Software Foundation; either version 2 of the License, or
   7     (at your option) any later version.
   8
   9     This program is distributed in the hope that it will be useful,
  10     but WITHOUT ANY WARRANTY; without even the implied warranty of
  11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12     GNU General Public License for more details.
  13
  14     You should have received a copy of the GNU General Public License
  15     along with this program; if not, write to the Free Software
  16     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  17 */
  18 #include <linux/ftrace.h>
  19 #include <linux/memory.h>
  20 #include <linux/extable.h>
  21 #include <linux/module.h>
  22 #include <linux/mutex.h>
  23 #include <linux/init.h>
  24 #include <linux/kprobes.h>
  25 #include <linux/filter.h>
  26
  27 #include <asm/sections.h>
  28 #include <linux/uaccess.h>
  29
  30 /*
  31  * mutex protecting text section modification (dynamic code patching).
  32  * some users need to sleep (allocating memory...) while they hold this lock.
  33  *
  34  * NOT exported to modules - patching kernel text is a really delicate matter.
  35  */
  36 DEFINE_MUTEX(text_mutex);
  37
  38 extern struct exception_table_entry __start___ex_table[];
  39 extern struct exception_table_entry __stop___ex_table[];
  40
  41 /* Cleared by build time tools if the table is already sorted. */
  42 u32 __initdata __visible main_extable_sort_needed = 1;
  43
  44 /* Sort the kernel's built-in exception table */
  45 void __init sort_main_extable(void)
  46 {
  47         if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) {
  48                 pr_notice("Sorting __ex_table...\n");
  49                 sort_extable(__start___ex_table, __stop___ex_table);
  50         }
  51 }
  52
  53 /* Given an address, look for it in the exception tables. */
  54 const struct exception_table_entry *search_exception_tables(unsigned long addr)
  55 {
  56         const struct exception_table_entry *e;
  57
  58         e = search_extable(__start___ex_table,
  59                            __stop___ex_table - __start___ex_table, addr);
  60         if (!e)
  61                 e = search_module_extables(addr);
  62         return e;
  63 }
  64
  65 static inline int init_kernel_text(unsigned long addr)
  66 {
  67         if (addr >= (unsigned long)_sinittext &&
  68             addr < (unsigned long)_einittext)
  69                 return 1;
  70         return 0;
  71 }
  72
  73 int notrace core_kernel_text(unsigned long addr)
  74 {
  75         if (addr >= (unsigned long)_stext &&
  76             addr < (unsigned long)_etext)
  77                 return 1;
  78
  79         if (system_state < SYSTEM_RUNNING &&
  80             init_kernel_text(addr))
  81                 return 1;
  82         return 0;
  83 }
  84
  85 /**
  86  * core_kernel_data - tell if addr points to kernel data
  87  * @addr: address to test
  88  *
  89  * Returns true if @addr passed in is from the core kernel data
  90  * section.
  91  *
  92  * Note: On some archs it may return true for core RODATA, and false
  93  *  for others. But will always be true for core RW data.
  94  */
  95 int core_kernel_data(unsigned long addr)
  96 {
  97         if (addr >= (unsigned long)_sdata &&
  98             addr < (unsigned long)_edata)
  99                 return 1;
 100         return 0;
 101 }
 102
 103 int __kernel_text_address(unsigned long addr)
 104 {
 105         if (kernel_text_address(addr))
 106                 return 1;
 107         /*
 108          * There might be init symbols in saved stacktraces.
 109          * Give those symbols a chance to be printed in
 110          * backtraces (such as lockdep traces).
 111          *
 112          * Since we are after the module-symbols check, there's
 113          * no danger of address overlap:
 114          */
 115         if (init_kernel_text(addr))
 116                 return 1;
 117         return 0;
 118 }
 119
 120 int kernel_text_address(unsigned long addr)
 121 {
 122         bool no_rcu;
 123         int ret = 1;
 124
 125         if (core_kernel_text(addr))
 126                 return 1;
 127
 128         /*
 129          * If a stack dump happens while RCU is not watching, then
 130          * RCU needs to be notified that it requires to start
 131          * watching again. This can happen either by tracing that
 132          * triggers a stack trace, or a WARN() that happens during
 133          * coming back from idle, or cpu on or offlining.
 134          *
 135          * is_module_text_address() as well as the kprobe slots
 136          * and is_bpf_text_address() require RCU to be watching.
 137          */
 138         no_rcu = !rcu_is_watching();
 139
 140         /* Treat this like an NMI as it can happen anywhere */
 141         if (no_rcu)
 142                 rcu_nmi_enter();
 143
 144         if (is_module_text_address(addr))
 145                 goto out;
 146         if (is_ftrace_trampoline(addr))
 147                 goto out;
 148         if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
 149                 goto out;
 150         if (is_bpf_text_address(addr))
 151                 goto out;
 152         ret = 0;
 153 out:
 154         if (no_rcu)
 155                 rcu_nmi_exit();
 156
 157         return ret;
 158 }
 159
 160 /*
 161  * On some architectures (PPC64, IA64) function pointers
 162  * are actually only tokens to some data that then holds the
 163  * real function address. As a result, to find if a function
 164  * pointer is part of the kernel text, we need to do some
 165  * special dereferencing first.
 166  */
 167 int func_ptr_is_kernel_text(void *ptr)
 168 {
 169         unsigned long addr;
 170         addr = (unsigned long) dereference_function_descriptor(ptr);
 171         if (core_kernel_text(addr))
 172                 return 1;
 173         return is_module_text_address(addr);
 174 }