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 } 171