arch/x86/include/asm/alternative.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _ASM_X86_ALTERNATIVE_H
   3 #define _ASM_X86_ALTERNATIVE_H
   4
   5 #include <linux/types.h>
   6 #include <linux/stringify.h>
   7 #include <asm/asm.h>
   8
   9 #define ALTINSTR_FLAG_INV       (1 << 15)
  10 #define ALT_NOT(feat)           ((feat) | ALTINSTR_FLAG_INV)
  11
  12 #ifndef __ASSEMBLY__
  13
  14 #include <linux/stddef.h>
  15
  16 /*
  17  * Alternative inline assembly for SMP.
  18  *
  19  * The LOCK_PREFIX macro defined here replaces the LOCK and
  20  * LOCK_PREFIX macros used everywhere in the source tree.
  21  *
  22  * SMP alternatives use the same data structures as the other
  23  * alternatives and the X86_FEATURE_UP flag to indicate the case of a
  24  * UP system running a SMP kernel.  The existing apply_alternatives()
  25  * works fine for patching a SMP kernel for UP.
  26  *
  27  * The SMP alternative tables can be kept after boot and contain both
  28  * UP and SMP versions of the instructions to allow switching back to
  29  * SMP at runtime, when hotplugging in a new CPU, which is especially
  30  * useful in virtualized environments.
  31  *
  32  * The very common lock prefix is handled as special case in a
  33  * separate table which is a pure address list without replacement ptr
  34  * and size information.  That keeps the table sizes small.
  35  */
  36
  37 #ifdef CONFIG_SMP
  38 #define LOCK_PREFIX_HERE \
  39                 ".pushsection .smp_locks,\"a\"\n"       \
  40                 ".balign 4\n"                           \
  41                 ".long 671f - .\n" /* offset */         \
  42                 ".popsection\n"                         \
  43                 "671:"
  44
  45 #define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
  46
  47 #else /* ! CONFIG_SMP */
  48 #define LOCK_PREFIX_HERE ""
  49 #define LOCK_PREFIX ""
  50 #endif
  51
  52 /*
  53  * objtool annotation to ignore the alternatives and only consider the original
  54  * instruction(s).
  55  */
  56 #define ANNOTATE_IGNORE_ALTERNATIVE                             \
  57         "999:\n\t"                                              \
  58         ".pushsection .discard.ignore_alts\n\t"                 \
  59         ".long 999b - .\n\t"                                    \
  60         ".popsection\n\t"
  61
  62 struct alt_instr {
  63         s32 instr_offset;       /* original instruction */
  64         s32 repl_offset;        /* offset to replacement instruction */
  65         u16 cpuid;              /* cpuid bit set for replacement */
  66         u8  instrlen;           /* length of original instruction */
  67         u8  replacementlen;     /* length of new instruction */
  68 } __packed;
  69
  70 /*
  71  * Debug flag that can be tested to see whether alternative
  72  * instructions were patched in already:
  73  */
  74 extern int alternatives_patched;
  75
  76 extern void alternative_instructions(void);
  77 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
  78 extern void apply_retpolines(s32 *start, s32 *end);
  79 extern void apply_returns(s32 *start, s32 *end);
  80
  81 struct module;
  82
  83 #ifdef CONFIG_SMP
  84 extern void alternatives_smp_module_add(struct module *mod, char *name,
  85                                         void *locks, void *locks_end,
  86                                         void *text, void *text_end);
  87 extern void alternatives_smp_module_del(struct module *mod);
  88 extern void alternatives_enable_smp(void);
  89 extern int alternatives_text_reserved(void *start, void *end);
  90 extern bool skip_smp_alternatives;
  91 #else
  92 static inline void alternatives_smp_module_add(struct module *mod, char *name,
  93                                                void *locks, void *locks_end,
  94                                                void *text, void *text_end) {}
  95 static inline void alternatives_smp_module_del(struct module *mod) {}
  96 static inline void alternatives_enable_smp(void) {}
  97 static inline int alternatives_text_reserved(void *start, void *end)
  98 {
  99         return 0;
 100 }
 101 #endif  /* CONFIG_SMP */
 102
 103 #define b_replacement(num)      "664"#num
 104 #define e_replacement(num)      "665"#num
 105
 106 #define alt_end_marker          "663"
 107 #define alt_slen                "662b-661b"
 108 #define alt_total_slen          alt_end_marker"b-661b"
 109 #define alt_rlen(num)           e_replacement(num)"f-"b_replacement(num)"f"
 110
 111 #define OLDINSTR(oldinstr, num)                                         \
 112         "# ALT: oldnstr\n"                                              \
 113         "661:\n\t" oldinstr "\n662:\n"                                  \
 114         "# ALT: padding\n"                                              \
 115         ".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * "          \
 116                 "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n"           \
 117         alt_end_marker ":\n"
 118
 119 /*
 120  * gas compatible max based on the idea from:
 121  * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
 122  *
 123  * The additional "-" is needed because gas uses a "true" value of -1.
 124  */
 125 #define alt_max_short(a, b)     "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"
 126
 127 /*
 128  * Pad the second replacement alternative with additional NOPs if it is
 129  * additionally longer than the first replacement alternative.
 130  */
 131 #define OLDINSTR_2(oldinstr, num1, num2) \
 132         "# ALT: oldinstr2\n"                                                                    \
 133         "661:\n\t" oldinstr "\n662:\n"                                                          \
 134         "# ALT: padding2\n"                                                                     \
 135         ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * "  \
 136                 "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n"  \
 137         alt_end_marker ":\n"
 138
 139 #define OLDINSTR_3(oldinsn, n1, n2, n3)                                                         \
 140         "# ALT: oldinstr3\n"                                                                    \
 141         "661:\n\t" oldinsn "\n662:\n"                                                           \
 142         "# ALT: padding3\n"                                                                     \
 143         ".skip -((" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3))      \
 144                 " - (" alt_slen ")) > 0) * "                                                    \
 145                 "(" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3))      \
 146                 " - (" alt_slen ")), 0x90\n"                                                    \
 147         alt_end_marker ":\n"
 148
 149 #define ALTINSTR_ENTRY(feature, num)                                          \
 150         " .long 661b - .\n"                             /* label           */ \
 151         " .long " b_replacement(num)"f - .\n"           /* new instruction */ \
 152         " .word " __stringify(feature) "\n"             /* feature bit     */ \
 153         " .byte " alt_total_slen "\n"                   /* source len      */ \
 154         " .byte " alt_rlen(num) "\n"                    /* replacement len */
 155
 156 #define ALTINSTR_REPLACEMENT(newinstr, num)             /* replacement */       \
 157         "# ALT: replacement " #num "\n"                                         \
 158         b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n"
 159
 160 /* alternative assembly primitive: */
 161 #define ALTERNATIVE(oldinstr, newinstr, feature)                        \
 162         OLDINSTR(oldinstr, 1)                                           \
 163         ".pushsection .altinstructions,\"a\"\n"                         \
 164         ALTINSTR_ENTRY(feature, 1)                                      \
 165         ".popsection\n"                                                 \
 166         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 167         ALTINSTR_REPLACEMENT(newinstr, 1)                               \
 168         ".popsection\n"
 169
 170 #define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
 171         OLDINSTR_2(oldinstr, 1, 2)                                      \
 172         ".pushsection .altinstructions,\"a\"\n"                         \
 173         ALTINSTR_ENTRY(feature1, 1)                                     \
 174         ALTINSTR_ENTRY(feature2, 2)                                     \
 175         ".popsection\n"                                                 \
 176         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 177         ALTINSTR_REPLACEMENT(newinstr1, 1)                              \
 178         ALTINSTR_REPLACEMENT(newinstr2, 2)                              \
 179         ".popsection\n"
 180
 181 /* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
 182 #define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr_yes, newinstr_no) \
 183         ALTERNATIVE_2(oldinstr, newinstr_no, X86_FEATURE_ALWAYS,        \
 184                       newinstr_yes, feature)
 185
 186 #define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \
 187         OLDINSTR_3(oldinsn, 1, 2, 3)                                            \
 188         ".pushsection .altinstructions,\"a\"\n"                                 \
 189         ALTINSTR_ENTRY(feat1, 1)                                                \
 190         ALTINSTR_ENTRY(feat2, 2)                                                \
 191         ALTINSTR_ENTRY(feat3, 3)                                                \
 192         ".popsection\n"                                                         \
 193         ".pushsection .altinstr_replacement, \"ax\"\n"                          \
 194         ALTINSTR_REPLACEMENT(newinsn1, 1)                                       \
 195         ALTINSTR_REPLACEMENT(newinsn2, 2)                                       \
 196         ALTINSTR_REPLACEMENT(newinsn3, 3)                                       \
 197         ".popsection\n"
 198
 199 /*
 200  * Alternative instructions for different CPU types or capabilities.
 201  *
 202  * This allows to use optimized instructions even on generic binary
 203  * kernels.
 204  *
 205  * length of oldinstr must be longer or equal the length of newinstr
 206  * It can be padded with nops as needed.
 207  *
 208  * For non barrier like inlines please define new variants
 209  * without volatile and memory clobber.
 210  */
 211 #define alternative(oldinstr, newinstr, feature)                        \
 212         asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
 213
 214 #define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
 215         asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
 216
 217 #define alternative_ternary(oldinstr, feature, newinstr_yes, newinstr_no) \
 218         asm_inline volatile(ALTERNATIVE_TERNARY(oldinstr, feature, newinstr_yes, newinstr_no) ::: "memory")
 219
 220 /*
 221  * Alternative inline assembly with input.
 222  *
 223  * Peculiarities:
 224  * No memory clobber here.
 225  * Argument numbers start with 1.
 226  * Leaving an unused argument 0 to keep API compatibility.
 227  */
 228 #define alternative_input(oldinstr, newinstr, feature, input...)        \
 229         asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature)   \
 230                 : : "i" (0), ## input)
 231
 232 /*
 233  * This is similar to alternative_input. But it has two features and
 234  * respective instructions.
 235  *
 236  * If CPU has feature2, newinstr2 is used.
 237  * Otherwise, if CPU has feature1, newinstr1 is used.
 238  * Otherwise, oldinstr is used.
 239  */
 240 #define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2,        \
 241                            feature2, input...)                               \
 242         asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1,     \
 243                 newinstr2, feature2)                                         \
 244                 : : "i" (0), ## input)
 245
 246 /* Like alternative_input, but with a single output argument */
 247 #define alternative_io(oldinstr, newinstr, feature, output, input...)   \
 248         asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature)   \
 249                 : output : "i" (0), ## input)
 250
 251 /* Like alternative_io, but for replacing a direct call with another one. */
 252 #define alternative_call(oldfunc, newfunc, feature, output, input...)   \
 253         asm_inline volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
 254                 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 255
 256 /*
 257  * Like alternative_call, but there are two features and respective functions.
 258  * If CPU has feature2, function2 is used.
 259  * Otherwise, if CPU has feature1, function1 is used.
 260  * Otherwise, old function is used.
 261  */
 262 #define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2,   \
 263                            output, input...)                                  \
 264         asm_inline volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
 265                 "call %P[new2]", feature2)                                    \
 266                 : output, ASM_CALL_CONSTRAINT                                 \
 267                 : [old] "i" (oldfunc), [new1] "i" (newfunc1),                 \
 268                   [new2] "i" (newfunc2), ## input)
 269
 270 /*
 271  * use this macro(s) if you need more than one output parameter
 272  * in alternative_io
 273  */
 274 #define ASM_OUTPUT2(a...) a
 275
 276 /*
 277  * use this macro if you need clobbers but no inputs in
 278  * alternative_{input,io,call}()
 279  */
 280 #define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
 281
 282 #else /* __ASSEMBLY__ */
 283
 284 #ifdef CONFIG_SMP
 285         .macro LOCK_PREFIX
 286 672:    lock
 287         .pushsection .smp_locks,"a"
 288         .balign 4
 289         .long 672b - .
 290         .popsection
 291         .endm
 292 #else
 293         .macro LOCK_PREFIX
 294         .endm
 295 #endif
 296
 297 /*
 298  * objtool annotation to ignore the alternatives and only consider the original
 299  * instruction(s).
 300  */
 301 .macro ANNOTATE_IGNORE_ALTERNATIVE
 302         .Lannotate_\@:
 303         .pushsection .discard.ignore_alts
 304         .long .Lannotate_\@ - .
 305         .popsection
 306 .endm
 307
 308 /*
 309  * Issue one struct alt_instr descriptor entry (need to put it into
 310  * the section .altinstructions, see below). This entry contains
 311  * enough information for the alternatives patching code to patch an
 312  * instruction. See apply_alternatives().
 313  */
 314 .macro altinstruction_entry orig alt feature orig_len alt_len
 315         .long \orig - .
 316         .long \alt - .
 317         .word \feature
 318         .byte \orig_len
 319         .byte \alt_len
 320 .endm
 321
 322 /*
 323  * Define an alternative between two instructions. If @feature is
 324  * present, early code in apply_alternatives() replaces @oldinstr with
 325  * @newinstr. ".skip" directive takes care of proper instruction padding
 326  * in case @newinstr is longer than @oldinstr.
 327  */
 328 .macro ALTERNATIVE oldinstr, newinstr, feature
 329 140:
 330         \oldinstr
 331 141:
 332         .skip -(((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)),0x90
 333 142:
 334
 335         .pushsection .altinstructions,"a"
 336         altinstruction_entry 140b,143f,\feature,142b-140b,144f-143f
 337         .popsection
 338
 339         .pushsection .altinstr_replacement,"ax"
 340 143:
 341         \newinstr
 342 144:
 343         .popsection
 344 .endm
 345
 346 #define old_len                 141b-140b
 347 #define new_len1                144f-143f
 348 #define new_len2                145f-144f
 349
 350 /*
 351  * gas compatible max based on the idea from:
 352  * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
 353  *
 354  * The additional "-" is needed because gas uses a "true" value of -1.
 355  */
 356 #define alt_max_short(a, b)     ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
 357
 358
 359 /*
 360  * Same as ALTERNATIVE macro above but for two alternatives. If CPU
 361  * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
 362  * @feature2, it replaces @oldinstr with @feature2.
 363  */
 364 .macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
 365 140:
 366         \oldinstr
 367 141:
 368         .skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
 369                 (alt_max_short(new_len1, new_len2) - (old_len)),0x90
 370 142:
 371
 372         .pushsection .altinstructions,"a"
 373         altinstruction_entry 140b,143f,\feature1,142b-140b,144f-143f
 374         altinstruction_entry 140b,144f,\feature2,142b-140b,145f-144f
 375         .popsection
 376
 377         .pushsection .altinstr_replacement,"ax"
 378 143:
 379         \newinstr1
 380 144:
 381         \newinstr2
 382 145:
 383         .popsection
 384 .endm
 385
 386 /* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
 387 #define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr_yes, newinstr_no) \
 388         ALTERNATIVE_2 oldinstr, newinstr_no, X86_FEATURE_ALWAYS,        \
 389         newinstr_yes, feature
 390
 391 #endif /* __ASSEMBLY__ */
 392
 393 #endif /* _ASM_X86_ALTERNATIVE_H */