xref: /openbmc/linux/kernel/extable.c (revision 493c1822)
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