arch/x86/mm/extable.c

   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 }