xref: /openbmc/linux/arch/x86/mm/extable.c (revision d2c43ff1)
1 #include <linux/extable.h>
2 #include <linux/uaccess.h>
3 #include <linux/sched/debug.h>
4 
5 #include <asm/traps.h>
6 #include <asm/kdebug.h>
7 
8 typedef bool (*ex_handler_t)(const struct exception_table_entry *,
9 			    struct pt_regs *, int);
10 
11 static inline unsigned long
12 ex_fixup_addr(const struct exception_table_entry *x)
13 {
14 	return (unsigned long)&x->fixup + x->fixup;
15 }
16 static inline ex_handler_t
17 ex_fixup_handler(const struct exception_table_entry *x)
18 {
19 	return (ex_handler_t)((unsigned long)&x->handler + x->handler);
20 }
21 
22 bool ex_handler_default(const struct exception_table_entry *fixup,
23 		       struct pt_regs *regs, int trapnr)
24 {
25 	regs->ip = ex_fixup_addr(fixup);
26 	return true;
27 }
28 EXPORT_SYMBOL(ex_handler_default);
29 
30 bool ex_handler_fault(const struct exception_table_entry *fixup,
31 		     struct pt_regs *regs, int trapnr)
32 {
33 	regs->ip = ex_fixup_addr(fixup);
34 	regs->ax = trapnr;
35 	return true;
36 }
37 EXPORT_SYMBOL_GPL(ex_handler_fault);
38 
39 bool ex_handler_ext(const struct exception_table_entry *fixup,
40 		   struct pt_regs *regs, int trapnr)
41 {
42 	/* Special hack for uaccess_err */
43 	current->thread.uaccess_err = 1;
44 	regs->ip = ex_fixup_addr(fixup);
45 	return true;
46 }
47 EXPORT_SYMBOL(ex_handler_ext);
48 
49 bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup,
50 			     struct pt_regs *regs, int trapnr)
51 {
52 	if (pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pF)\n",
53 			 (unsigned int)regs->cx, regs->ip, (void *)regs->ip))
54 		show_stack_regs(regs);
55 
56 	/* Pretend that the read succeeded and returned 0. */
57 	regs->ip = ex_fixup_addr(fixup);
58 	regs->ax = 0;
59 	regs->dx = 0;
60 	return true;
61 }
62 EXPORT_SYMBOL(ex_handler_rdmsr_unsafe);
63 
64 bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup,
65 			     struct pt_regs *regs, int trapnr)
66 {
67 	if (pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pF)\n",
68 			 (unsigned int)regs->cx, (unsigned int)regs->dx,
69 			 (unsigned int)regs->ax,  regs->ip, (void *)regs->ip))
70 		show_stack_regs(regs);
71 
72 	/* Pretend that the write succeeded. */
73 	regs->ip = ex_fixup_addr(fixup);
74 	return true;
75 }
76 EXPORT_SYMBOL(ex_handler_wrmsr_unsafe);
77 
78 bool ex_handler_clear_fs(const struct exception_table_entry *fixup,
79 			 struct pt_regs *regs, int trapnr)
80 {
81 	if (static_cpu_has(X86_BUG_NULL_SEG))
82 		asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS));
83 	asm volatile ("mov %0, %%fs" : : "rm" (0));
84 	return ex_handler_default(fixup, regs, trapnr);
85 }
86 EXPORT_SYMBOL(ex_handler_clear_fs);
87 
88 bool ex_has_fault_handler(unsigned long ip)
89 {
90 	const struct exception_table_entry *e;
91 	ex_handler_t handler;
92 
93 	e = search_exception_tables(ip);
94 	if (!e)
95 		return false;
96 	handler = ex_fixup_handler(e);
97 
98 	return handler == ex_handler_fault;
99 }
100 
101 int fixup_exception(struct pt_regs *regs, int trapnr)
102 {
103 	const struct exception_table_entry *e;
104 	ex_handler_t handler;
105 
106 #ifdef CONFIG_PNPBIOS
107 	if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
108 		extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp;
109 		extern u32 pnp_bios_is_utter_crap;
110 		pnp_bios_is_utter_crap = 1;
111 		printk(KERN_CRIT "PNPBIOS fault.. attempting recovery.\n");
112 		__asm__ volatile(
113 			"movl %0, %%esp\n\t"
114 			"jmp *%1\n\t"
115 			: : "g" (pnp_bios_fault_esp), "g" (pnp_bios_fault_eip));
116 		panic("do_trap: can't hit this");
117 	}
118 #endif
119 
120 	e = search_exception_tables(regs->ip);
121 	if (!e)
122 		return 0;
123 
124 	handler = ex_fixup_handler(e);
125 	return handler(e, regs, trapnr);
126 }
127 
128 extern unsigned int early_recursion_flag;
129 
130 /* Restricted version used during very early boot */
131 void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
132 {
133 	/* Ignore early NMIs. */
134 	if (trapnr == X86_TRAP_NMI)
135 		return;
136 
137 	if (early_recursion_flag > 2)
138 		goto halt_loop;
139 
140 	/*
141 	 * Old CPUs leave the high bits of CS on the stack
142 	 * undefined.  I'm not sure which CPUs do this, but at least
143 	 * the 486 DX works this way.
144 	 */
145 	if ((regs->cs & 0xFFFF) != __KERNEL_CS)
146 		goto fail;
147 
148 	/*
149 	 * The full exception fixup machinery is available as soon as
150 	 * the early IDT is loaded.  This means that it is the
151 	 * responsibility of extable users to either function correctly
152 	 * when handlers are invoked early or to simply avoid causing
153 	 * exceptions before they're ready to handle them.
154 	 *
155 	 * This is better than filtering which handlers can be used,
156 	 * because refusing to call a handler here is guaranteed to
157 	 * result in a hard-to-debug panic.
158 	 *
159 	 * Keep in mind that not all vectors actually get here.  Early
160 	 * fage faults, for example, are special.
161 	 */
162 	if (fixup_exception(regs, trapnr))
163 		return;
164 
165 	if (fixup_bug(regs, trapnr))
166 		return;
167 
168 fail:
169 	early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n",
170 		     (unsigned)trapnr, (unsigned long)regs->cs, regs->ip,
171 		     regs->orig_ax, read_cr2());
172 
173 	show_regs(regs);
174 
175 halt_loop:
176 	while (true)
177 		halt();
178 }
179