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 &&
  38             &__stop___ex_table > &__start___ex_table) {
  39                 pr_notice("Sorting __ex_table...\n");
  40                 sort_extable(__start___ex_table, __stop___ex_table);
  41         }
  42 }
  43
  44 /* Given an address, look for it in the kernel exception table */
  45 const
  46 struct exception_table_entry *search_kernel_exception_table(unsigned long addr)
  47 {
  48         return search_extable(__start___ex_table,
  49                               __stop___ex_table - __start___ex_table, addr);
  50 }
  51
  52 /* Given an address, look for it in the exception tables. */
  53 const struct exception_table_entry *search_exception_tables(unsigned long addr)
  54 {
  55         const struct exception_table_entry *e;
  56
  57         e = search_kernel_exception_table(addr);
  58         if (!e)
  59                 e = search_module_extables(addr);
  60         if (!e)
  61                 e = search_bpf_extables(addr);
  62         return e;
  63 }
  64
  65 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          * is_bpf_text_address() and is_bpf_image_address require
 137          * RCU to be watching.
 138          */
 139         no_rcu = !rcu_is_watching();
 140
 141         /* Treat this like an NMI as it can happen anywhere */
 142         if (no_rcu)
 143                 rcu_nmi_enter();
 144
 145         if (is_module_text_address(addr))
 146                 goto out;
 147         if (is_ftrace_trampoline(addr))
 148                 goto out;
 149         if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
 150                 goto out;
 151         if (is_bpf_text_address(addr))
 152                 goto out;
 153         ret = 0;
 154 out:
 155         if (no_rcu)
 156                 rcu_nmi_exit();
 157
 158         return ret;
 159 }
 160
 161 /*
 162  * On some architectures (PPC64, IA64) function pointers
 163  * are actually only tokens to some data that then holds the
 164  * real function address. As a result, to find if a function
 165  * pointer is part of the kernel text, we need to do some
 166  * special dereferencing first.
 167  */
 168 int func_ptr_is_kernel_text(void *ptr)
 169 {
 170         unsigned long addr;
 171         addr = (unsigned long) dereference_function_descriptor(ptr);
 172         if (core_kernel_text(addr))
 173                 return 1;
 174         return is_module_text_address(addr);
 175 }