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 */
sort_main_extable(void)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
search_kernel_exception_table(unsigned long addr)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. */
search_exception_tables(unsigned long addr)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
core_kernel_text(unsigned long addr)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
__kernel_text_address(unsigned long addr)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
kernel_text_address(unsigned long addr)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
dereference_function_descriptor(void * ptr)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
dereference_kernel_function_descriptor(void * ptr)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
func_ptr_is_kernel_text(void * ptr)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