kernel/extable.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Rewritten by Rusty Russell, on the backs of many others...
   3    Copyright (C) 2001 Rusty Russell, 2002 Rusty Russell IBM.
   4
   5 */
   6 #include <linux/ftrace.h>
   7 #include <linux/memory.h>
   8 #include <linux/extable.h>
   9 #include <linux/module.h>
  10 #include <linux/mutex.h>
  11 #include <linux/init.h>
  12 #include <linux/kprobes.h>
  13 #include <linux/filter.h>
  14
  15 #include <asm/sections.h>
  16 #include <linux/uaccess.h>
  17
  18 /*
  19  * mutex protecting text section modification (dynamic code patching).
  20  * some users need to sleep (allocating memory...) while they hold this lock.
  21  *
  22  * Note: Also protects SMP-alternatives modification on x86.
  23  *
  24  * NOT exported to modules - patching kernel text is a really delicate matter.
  25  */
  26 DEFINE_MUTEX(text_mutex);
  27
  28 extern struct exception_table_entry __start___ex_table[];
  29 extern struct exception_table_entry __stop___ex_table[];
  30
  31 /* Cleared by build time tools if the table is already sorted. */
  32 u32 __initdata __visible main_extable_sort_needed = 1;
  33
  34 /* Sort the kernel's built-in exception table */
  35 void __init sort_main_extable(void)
  36 {
  37         if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) {
  38                 pr_notice("Sorting __ex_table...\n");
  39                 sort_extable(__start___ex_table, __stop___ex_table);
  40         }
  41 }
  42
  43 /* Given an address, look for it in the exception tables. */
  44 const struct exception_table_entry *search_exception_tables(unsigned long addr)
  45 {
  46         const struct exception_table_entry *e;
  47
  48         e = search_extable(__start___ex_table,
  49                            __stop___ex_table - __start___ex_table, addr);
  50         if (!e)
  51                 e = search_module_extables(addr);
  52         return e;
  53 }
  54
  55 int init_kernel_text(unsigned long addr)
  56 {
  57         if (addr >= (unsigned long)_sinittext &&
  58             addr < (unsigned long)_einittext)
  59                 return 1;
  60         return 0;
  61 }
  62
  63 int notrace core_kernel_text(unsigned long addr)
  64 {
  65         if (addr >= (unsigned long)_stext &&
  66             addr < (unsigned long)_etext)
  67                 return 1;
  68
  69         if (system_state < SYSTEM_RUNNING &&
  70             init_kernel_text(addr))
  71                 return 1;
  72         return 0;
  73 }
  74
  75 /**
  76  * core_kernel_data - tell if addr points to kernel data
  77  * @addr: address to test
  78  *
  79  * Returns true if @addr passed in is from the core kernel data
  80  * section.
  81  *
  82  * Note: On some archs it may return true for core RODATA, and false
  83  *  for others. But will always be true for core RW data.
  84  */
  85 int core_kernel_data(unsigned long addr)
  86 {
  87         if (addr >= (unsigned long)_sdata &&
  88             addr < (unsigned long)_edata)
  89                 return 1;
  90         return 0;
  91 }
  92
  93 int __kernel_text_address(unsigned long addr)
  94 {
  95         if (kernel_text_address(addr))
  96                 return 1;
  97         /*
  98          * There might be init symbols in saved stacktraces.
  99          * Give those symbols a chance to be printed in
 100          * backtraces (such as lockdep traces).
 101          *
 102          * Since we are after the module-symbols check, there's
 103          * no danger of address overlap:
 104          */
 105         if (init_kernel_text(addr))
 106                 return 1;
 107         return 0;
 108 }
 109
 110 int kernel_text_address(unsigned long addr)
 111 {
 112         bool no_rcu;
 113         int ret = 1;
 114
 115         if (core_kernel_text(addr))
 116                 return 1;
 117
 118         /*
 119          * If a stack dump happens while RCU is not watching, then
 120          * RCU needs to be notified that it requires to start
 121          * watching again. This can happen either by tracing that
 122          * triggers a stack trace, or a WARN() that happens during
 123          * coming back from idle, or cpu on or offlining.
 124          *
 125          * is_module_text_address() as well as the kprobe slots
 126          * and is_bpf_text_address() require RCU to be watching.
 127          */
 128         no_rcu = !rcu_is_watching();
 129
 130         /* Treat this like an NMI as it can happen anywhere */
 131         if (no_rcu)
 132                 rcu_nmi_enter();
 133
 134         if (is_module_text_address(addr))
 135                 goto out;
 136         if (is_ftrace_trampoline(addr))
 137                 goto out;
 138         if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
 139                 goto out;
 140         if (is_bpf_text_address(addr))
 141                 goto out;
 142         ret = 0;
 143 out:
 144         if (no_rcu)
 145                 rcu_nmi_exit();
 146
 147         return ret;
 148 }
 149
 150 /*
 151  * On some architectures (PPC64, IA64) function pointers
 152  * are actually only tokens to some data that then holds the
 153  * real function address. As a result, to find if a function
 154  * pointer is part of the kernel text, we need to do some
 155  * special dereferencing first.
 156  */
 157 int func_ptr_is_kernel_text(void *ptr)
 158 {
 159         unsigned long addr;
 160         addr = (unsigned long) dereference_function_descriptor(ptr);
 161         if (core_kernel_text(addr))
 162                 return 1;
 163         return is_module_text_address(addr);
 164 }