arch/x86/mm/extable.c

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