arch/x86/include/asm/alternative.h

   1 #ifndef _ASM_X86_ALTERNATIVE_H
   2 #define _ASM_X86_ALTERNATIVE_H
   3
   4 #include <linux/types.h>
   5 #include <linux/stddef.h>
   6 #include <linux/stringify.h>
   7 #include <asm/asm.h>
   8 #include <asm/ptrace.h>
   9
  10 /*
  11  * Alternative inline assembly for SMP.
  12  *
  13  * The LOCK_PREFIX macro defined here replaces the LOCK and
  14  * LOCK_PREFIX macros used everywhere in the source tree.
  15  *
  16  * SMP alternatives use the same data structures as the other
  17  * alternatives and the X86_FEATURE_UP flag to indicate the case of a
  18  * UP system running a SMP kernel.  The existing apply_alternatives()
  19  * works fine for patching a SMP kernel for UP.
  20  *
  21  * The SMP alternative tables can be kept after boot and contain both
  22  * UP and SMP versions of the instructions to allow switching back to
  23  * SMP at runtime, when hotplugging in a new CPU, which is especially
  24  * useful in virtualized environments.
  25  *
  26  * The very common lock prefix is handled as special case in a
  27  * separate table which is a pure address list without replacement ptr
  28  * and size information.  That keeps the table sizes small.
  29  */
  30
  31 #ifdef CONFIG_SMP
  32 #define LOCK_PREFIX_HERE \
  33                 ".pushsection .smp_locks,\"a\"\n"       \
  34                 ".balign 4\n"                           \
  35                 ".long 671f - .\n" /* offset */         \
  36                 ".popsection\n"                         \
  37                 "671:"
  38
  39 #define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
  40
  41 #else /* ! CONFIG_SMP */
  42 #define LOCK_PREFIX_HERE ""
  43 #define LOCK_PREFIX ""
  44 #endif
  45
  46 struct alt_instr {
  47         s32 instr_offset;       /* original instruction */
  48         s32 repl_offset;        /* offset to replacement instruction */
  49         u16 cpuid;              /* cpuid bit set for replacement */
  50         u8  instrlen;           /* length of original instruction */
  51         u8  replacementlen;     /* length of new instruction */
  52         u8  padlen;             /* length of build-time padding */
  53 } __packed;
  54
  55 /*
  56  * Debug flag that can be tested to see whether alternative
  57  * instructions were patched in already:
  58  */
  59 extern int alternatives_patched;
  60
  61 extern void alternative_instructions(void);
  62 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  63
  64 struct module;
  65
  66 #ifdef CONFIG_SMP
  67 extern void alternatives_smp_module_add(struct module *mod, char *name,
  68                                         void *locks, void *locks_end,
  69                                         void *text, void *text_end);
  70 extern void alternatives_smp_module_del(struct module *mod);
  71 extern void alternatives_enable_smp(void);
  72 extern int alternatives_text_reserved(void *start, void *end);
  73 extern bool skip_smp_alternatives;
  74 #else
  75 static inline void alternatives_smp_module_add(struct module *mod, char *name,
  76                                                void *locks, void *locks_end,
  77                                                void *text, void *text_end) {}
  78 static inline void alternatives_smp_module_del(struct module *mod) {}
  79 static inline void alternatives_enable_smp(void) {}
  80 static inline int alternatives_text_reserved(void *start, void *end)
  81 {
  82         return 0;
  83 }
  84 #endif  /* CONFIG_SMP */
  85
  86 #define b_replacement(num)      "664"#num
  87 #define e_replacement(num)      "665"#num
  88
  89 #define alt_end_marker          "663"
  90 #define alt_slen                "662b-661b"
  91 #define alt_pad_len             alt_end_marker"b-662b"
  92 #define alt_total_slen          alt_end_marker"b-661b"
  93 #define alt_rlen(num)           e_replacement(num)"f-"b_replacement(num)"f"
  94
  95 #define __OLDINSTR(oldinstr, num)                                       \
  96         "661:\n\t" oldinstr "\n662:\n"                                  \
  97         ".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * "          \
  98                 "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n"
  99
 100 #define OLDINSTR(oldinstr, num)                                         \
 101         __OLDINSTR(oldinstr, num)                                       \
 102         alt_end_marker ":\n"
 103
 104 /*
 105  * max without conditionals. Idea adapted from:
 106  * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
 107  *
 108  * The additional "-" is needed because gas works with s32s.
 109  */
 110 #define alt_max_short(a, b)     "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") - (" b ")))))"
 111
 112 /*
 113  * Pad the second replacement alternative with additional NOPs if it is
 114  * additionally longer than the first replacement alternative.
 115  */
 116 #define OLDINSTR_2(oldinstr, num1, num2) \
 117         "661:\n\t" oldinstr "\n662:\n"                                                          \
 118         ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * "  \
 119                 "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n"  \
 120         alt_end_marker ":\n"
 121
 122 #define ALTINSTR_ENTRY(feature, num)                                          \
 123         " .long 661b - .\n"                             /* label           */ \
 124         " .long " b_replacement(num)"f - .\n"           /* new instruction */ \
 125         " .word " __stringify(feature) "\n"             /* feature bit     */ \
 126         " .byte " alt_total_slen "\n"                   /* source len      */ \
 127         " .byte " alt_rlen(num) "\n"                    /* replacement len */ \
 128         " .byte " alt_pad_len "\n"                      /* pad len */
 129
 130 #define ALTINSTR_REPLACEMENT(newinstr, feature, num)    /* replacement */     \
 131         b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n\t"
 132
 133 /* alternative assembly primitive: */
 134 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
 135         OLDINSTR(oldinstr, 1)                                           \
 136         ".pushsection .altinstructions,\"a\"\n"                         \
 137         ALTINSTR_ENTRY(feature, 1)                                      \
 138         ".popsection\n"                                                 \
 139         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 140         ALTINSTR_REPLACEMENT(newinstr, feature, 1)                      \
 141         ".popsection"
 142
 143 #define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
 144         OLDINSTR_2(oldinstr, 1, 2)                                      \
 145         ".pushsection .altinstructions,\"a\"\n"                         \
 146         ALTINSTR_ENTRY(feature1, 1)                                     \
 147         ALTINSTR_ENTRY(feature2, 2)                                     \
 148         ".popsection\n"                                                 \
 149         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 150         ALTINSTR_REPLACEMENT(newinstr1, feature1, 1)                    \
 151         ALTINSTR_REPLACEMENT(newinstr2, feature2, 2)                    \
 152         ".popsection"
 153
 154 /*
 155  * Alternative instructions for different CPU types or capabilities.
 156  *
 157  * This allows to use optimized instructions even on generic binary
 158  * kernels.
 159  *
 160  * length of oldinstr must be longer or equal the length of newinstr
 161  * It can be padded with nops as needed.
 162  *
 163  * For non barrier like inlines please define new variants
 164  * without volatile and memory clobber.
 165  */
 166 #define alternative(oldinstr, newinstr, feature)                        \
 167         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 168
 169 #define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
 170         asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
 171
 172 /*
 173  * Alternative inline assembly with input.
 174  *
 175  * Pecularities:
 176  * No memory clobber here.
 177  * Argument numbers start with 1.
 178  * Best is to use constraints that are fixed size (like (%1) ... "r")
 179  * If you use variable sized constraints like "m" or "g" in the
 180  * replacement make sure to pad to the worst case length.
 181  * Leaving an unused argument 0 to keep API compatibility.
 182  */
 183 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 184         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 185                 : : "i" (0), ## input)
 186
 187 /*
 188  * This is similar to alternative_input. But it has two features and
 189  * respective instructions.
 190  *
 191  * If CPU has feature2, newinstr2 is used.
 192  * Otherwise, if CPU has feature1, newinstr1 is used.
 193  * Otherwise, oldinstr is used.
 194  */
 195 #define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2,        \
 196                            feature2, input...)                               \
 197         asm volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1,            \
 198                 newinstr2, feature2)                                         \
 199                 : : "i" (0), ## input)
 200
 201 /* Like alternative_input, but with a single output argument */
 202 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 203         asm volatile (ALTERNATIVE(oldinstr, newinstr, feature)          \
 204                 : output : "i" (0), ## input)
 205
 206 /* Like alternative_io, but for replacing a direct call with another one. */
 207 #define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 208         asm volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 209                 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 210
 211 /*
 212  * Like alternative_call, but there are two features and respective functions.
 213  * If CPU has feature2, function2 is used.
 214  * Otherwise, if CPU has feature1, function1 is used.
 215  * Otherwise, old function is used.
 216  */
 217 #define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
 218                            output, input...)                                  \
 219         asm volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
 220                 "call %P[new2]", feature2)                                    \
 221                 : output : [old] "i" (oldfunc), [new1] "i" (newfunc1),        \
 222                 [new2] "i" (newfunc2), ## input)
 223
 224 /*
 225  * use this macro(s) if you need more than one output parameter
 226  * in alternative_io
 227  */
 228 #define ASM_OUTPUT2(a...) a
 229
 230 /*
 231  * use this macro if you need clobbers but no inputs in
 232  * alternative_{input,io,call}()
 233  */
 234 #define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
 235
 236 struct paravirt_patch_site;
 237 #ifdef CONFIG_PARAVIRT
 238 void apply_paravirt(struct paravirt_patch_site *start,
 239                     struct paravirt_patch_site *end);
 240 #else
 241 static inline void apply_paravirt(struct paravirt_patch_site *start,
 242                                   struct paravirt_patch_site *end)
 243 {}
 244 #define __parainstructions      NULL
 245 #define __parainstructions_end  NULL
 246 #endif
 247
 248 extern void *text_poke_early(void *addr, const void *opcode, size_t len);
 249
 250 /*
 251  * Clear and restore the kernel write-protection flag on the local CPU.
 252  * Allows the kernel to edit read-only pages.
 253  * Side-effect: any interrupt handler running between save and restore will have
 254  * the ability to write to read-only pages.
 255  *
 256  * Warning:
 257  * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
 258  * no thread can be preempted in the instructions being modified (no iret to an
 259  * invalid instruction possible) or if the instructions are changed from a
 260  * consistent state to another consistent state atomically.
 261  * On the local CPU you need to be protected again NMI or MCE handlers seeing an
 262  * inconsistent instruction while you patch.
 263  */
 264 extern void *text_poke(void *addr, const void *opcode, size_t len);
 265 extern int poke_int3_handler(struct pt_regs *regs);
 266 extern void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler);
 267
 268 #endif /* _ASM_X86_ALTERNATIVE_H */