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/elf.h>
   7 #include <linux/ftrace.h>
   8 #include <linux/memory.h>
   9 #include <linux/extable.h>
  10 #include <linux/module.h>
  11 #include <linux/mutex.h>
  12 #include <linux/init.h>
  13 #include <linux/kprobes.h>
  14 #include <linux/filter.h>
  15
  16 #include <asm/sections.h>
  17 #include <linux/uaccess.h>
  18
  19 /*
  20  * mutex protecting text section modification (dynamic code patching).
  21  * some users need to sleep (allocating memory...) while they hold this lock.
  22  *
  23  * Note: Also protects SMP-alternatives modification on x86.
  24  *
  25  * NOT exported to modules - patching kernel text is a really delicate matter.
  26  */
  27 DEFINE_MUTEX(text_mutex);
  28
  29 extern struct exception_table_entry __start___ex_table[];
  30 extern struct exception_table_entry __stop___ex_table[];
  31
  32 /* Cleared by build time tools if the table is already sorted. */
  33 u32 __initdata __visible main_extable_sort_needed = 1;
  34
  35 /* Sort the kernel's built-in exception table */
  36 void __init sort_main_extable(void)
  37 {
  38         if (main_extable_sort_needed &&
  39             &__stop___ex_table > &__start___ex_table) {
  40                 pr_notice("Sorting __ex_table...\n");
  41                 sort_extable(__start___ex_table, __stop___ex_table);
  42         }
  43 }
  44
  45 /* Given an address, look for it in the kernel exception table */
  46 const
  47 struct exception_table_entry *search_kernel_exception_table(unsigned long addr)
  48 {
  49         return search_extable(__start___ex_table,
  50                               __stop___ex_table - __start___ex_table, addr);
  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_kernel_exception_table(addr);
  59         if (!e)
  60                 e = search_module_extables(addr);
  61         if (!e)
  62                 e = search_bpf_extables(addr);
  63         return e;
  64 }
  65
  66 int notrace core_kernel_text(unsigned long addr)
  67 {
  68         if (is_kernel_text(addr))
  69                 return 1;
  70
  71         if (system_state < SYSTEM_FREEING_INITMEM &&
  72             is_kernel_inittext(addr))
  73                 return 1;
  74         return 0;
  75 }
  76
  77 int __kernel_text_address(unsigned long addr)
  78 {
  79         if (kernel_text_address(addr))
  80                 return 1;
  81         /*
  82          * There might be init symbols in saved stacktraces.
  83          * Give those symbols a chance to be printed in
  84          * backtraces (such as lockdep traces).
  85          *
  86          * Since we are after the module-symbols check, there's
  87          * no danger of address overlap:
  88          */
  89         if (is_kernel_inittext(addr))
  90                 return 1;
  91         return 0;
  92 }
  93
  94 int kernel_text_address(unsigned long addr)
  95 {
  96         bool no_rcu;
  97         int ret = 1;
  98
  99         if (core_kernel_text(addr))
 100                 return 1;
 101
 102         /*
 103          * If a stack dump happens while RCU is not watching, then
 104          * RCU needs to be notified that it requires to start
 105          * watching again. This can happen either by tracing that
 106          * triggers a stack trace, or a WARN() that happens during
 107          * coming back from idle, or cpu on or offlining.
 108          *
 109          * is_module_text_address() as well as the kprobe slots,
 110          * is_bpf_text_address() and is_bpf_image_address require
 111          * RCU to be watching.
 112          */
 113         no_rcu = !rcu_is_watching();
 114
 115         /* Treat this like an NMI as it can happen anywhere */
 116         if (no_rcu)
 117                 ct_nmi_enter();
 118
 119         if (is_module_text_address(addr))
 120                 goto out;
 121         if (is_ftrace_trampoline(addr))
 122                 goto out;
 123         if (is_kprobe_optinsn_slot(addr) || is_kprobe_insn_slot(addr))
 124                 goto out;
 125         if (is_bpf_text_address(addr))
 126                 goto out;
 127         ret = 0;
 128 out:
 129         if (no_rcu)
 130                 ct_nmi_exit();
 131
 132         return ret;
 133 }
 134
 135 /*
 136  * On some architectures (PPC64, IA64, PARISC) function pointers
 137  * are actually only tokens to some data that then holds the
 138  * real function address. As a result, to find if a function
 139  * pointer is part of the kernel text, we need to do some
 140  * special dereferencing first.
 141  */
 142 #ifdef CONFIG_HAVE_FUNCTION_DESCRIPTORS
 143 void *dereference_function_descriptor(void *ptr)
 144 {
 145         func_desc_t *desc = ptr;
 146         void *p;
 147
 148         if (!get_kernel_nofault(p, (void *)&desc->addr))
 149                 ptr = p;
 150         return ptr;
 151 }
 152 EXPORT_SYMBOL_GPL(dereference_function_descriptor);
 153
 154 void *dereference_kernel_function_descriptor(void *ptr)
 155 {
 156         if (ptr < (void *)__start_opd || ptr >= (void *)__end_opd)
 157                 return ptr;
 158
 159         return dereference_function_descriptor(ptr);
 160 }
 161 #endif
 162
 163 int func_ptr_is_kernel_text(void *ptr)
 164 {
 165         unsigned long addr;
 166         addr = (unsigned long) dereference_function_descriptor(ptr);
 167         if (core_kernel_text(addr))
 168                 return 1;
 169         return is_module_text_address(addr);
 170 }