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  * Note: Also protects SMP-alternatives modification on x86.
  35  *
  36  * NOT exported to modules - patching kernel text is a really delicate matter.
  37  */
  38 DEFINE_MUTEX(text_mutex);
  39
  40 extern struct exception_table_entry __start___ex_table[];
  41 extern struct exception_table_entry __stop___ex_table[];
  42
  43 /* Cleared by build time tools if the table is already sorted. */
  44 u32 __initdata __visible main_extable_sort_needed = 1;
  45
  46 /* Sort the kernel's built-in exception table */
  47 void __init sort_main_extable(void)
  48 {
  49         if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) {
  50                 pr_notice("Sorting __ex_table...\n");
  51                 sort_extable(__start___ex_table, __stop___ex_table);
  52         }
  53 }
  54
  55 /* Given an address, look for it in the exception tables. */
  56 const struct exception_table_entry *search_exception_tables(unsigned long addr)
  57 {
  58         const struct exception_table_entry *e;
  59
  60         e = search_extable(__start___ex_table,
  61                            __stop___ex_table - __start___ex_table, addr);
  62         if (!e)
  63                 e = search_module_extables(addr);
  64         return e;
  65 }
  66
  67 static inline int init_kernel_text(unsigned long addr)
  68 {
  69         if (addr >= (unsigned long)_sinittext &&
  70             addr < (unsigned long)_einittext)
  71                 return 1;
  72         return 0;
  73 }
  74
  75 int notrace core_kernel_text(unsigned long addr)
  76 {
  77         if (addr >= (unsigned long)_stext &&
  78             addr < (unsigned long)_etext)
  79                 return 1;
  80
  81         if (system_state < SYSTEM_RUNNING &&
  82             init_kernel_text(addr))
  83                 return 1;
  84         return 0;
  85 }
  86
  87 /**
  88  * core_kernel_data - tell if addr points to kernel data
  89  * @addr: address to test
  90  *
  91  * Returns true if @addr passed in is from the core kernel data
  92  * section.
  93  *
  94  * Note: On some archs it may return true for core RODATA, and false
  95  *  for others. But will always be true for core RW data.
  96  */
  97 int core_kernel_data(unsigned long addr)
  98 {
  99         if (addr >= (unsigned long)_sdata &&
 100             addr < (unsigned long)_edata)
 101                 return 1;
 102         return 0;
 103 }
 104
 105 int __kernel_text_address(unsigned long addr)
 106 {
 107         if (kernel_text_address(addr))
 108                 return 1;
 109         /*
 110          * There might be init symbols in saved stacktraces.
 111          * Give those symbols a chance to be printed in
 112          * backtraces (such as lockdep traces).
 113          *
 114          * Since we are after the module-symbols check, there's
 115          * no danger of address overlap:
 116          */
 117         if (init_kernel_text(addr))
 118                 return 1;
 119         return 0;
 120 }
 121
 122 int kernel_text_address(unsigned long addr)
 123 {
 124         bool no_rcu;
 125         int ret = 1;
 126
 127         if (core_kernel_text(addr))
 128                 return 1;
 129
 130         /*
 131          * If a stack dump happens while RCU is not watching, then
 132          * RCU needs to be notified that it requires to start
 133          * watching again. This can happen either by tracing that
 134          * triggers a stack trace, or a WARN() that happens during
 135          * coming back from idle, or cpu on or offlining.
 136          *
 137          * is_module_text_address() as well as the kprobe slots
 138          * and is_bpf_text_address() require RCU to be watching.
 139          */
 140         no_rcu = !rcu_is_watching();
 141
 142         /* Treat this like an NMI as it can happen anywhere */
 143         if (no_rcu)
 144                 rcu_nmi_enter();
 145
 146         if (is_module_text_address(addr))
 147                 goto out;
 148         if (is_ftrace_trampoline(addr))
 149                 goto out;
 150         if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
 151                 goto out;
 152         if (is_bpf_text_address(addr))
 153                 goto out;
 154         ret = 0;
 155 out:
 156         if (no_rcu)
 157                 rcu_nmi_exit();
 158
 159         return ret;
 160 }
 161
 162 /*
 163  * On some architectures (PPC64, IA64) function pointers
 164  * are actually only tokens to some data that then holds the
 165  * real function address. As a result, to find if a function
 166  * pointer is part of the kernel text, we need to do some
 167  * special dereferencing first.
 168  */
 169 int func_ptr_is_kernel_text(void *ptr)
 170 {
 171         unsigned long addr;
 172         addr = (unsigned long) dereference_function_descriptor(ptr);
 173         if (core_kernel_text(addr))
 174                 return 1;
 175         return is_module_text_address(addr);
 176 }