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