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 <linux/objtool.h>
   8 #include <asm/asm.h>
   9
  10 #define ALT_FLAGS_SHIFT         16
  11
  12 #define ALT_FLAG_NOT            (1 << 0)
  13 #define ALT_NOT(feature)        ((ALT_FLAG_NOT << ALT_FLAGS_SHIFT) | (feature))
  14 #define ALT_FLAG_DIRECT_CALL    (1 << 1)
  15 #define ALT_DIRECT_CALL(feature) ((ALT_FLAG_DIRECT_CALL << ALT_FLAGS_SHIFT) | (feature))
  16 #define ALT_CALL_ALWAYS         ALT_DIRECT_CALL(X86_FEATURE_ALWAYS)
  17
  18 #ifndef __ASSEMBLY__
  19
  20 #include <linux/stddef.h>
  21
  22 /*
  23  * Alternative inline assembly for SMP.
  24  *
  25  * The LOCK_PREFIX macro defined here replaces the LOCK and
  26  * LOCK_PREFIX macros used everywhere in the source tree.
  27  *
  28  * SMP alternatives use the same data structures as the other
  29  * alternatives and the X86_FEATURE_UP flag to indicate the case of a
  30  * UP system running a SMP kernel.  The existing apply_alternatives()
  31  * works fine for patching a SMP kernel for UP.
  32  *
  33  * The SMP alternative tables can be kept after boot and contain both
  34  * UP and SMP versions of the instructions to allow switching back to
  35  * SMP at runtime, when hotplugging in a new CPU, which is especially
  36  * useful in virtualized environments.
  37  *
  38  * The very common lock prefix is handled as special case in a
  39  * separate table which is a pure address list without replacement ptr
  40  * and size information.  That keeps the table sizes small.
  41  */
  42
  43 #ifdef CONFIG_SMP
  44 #define LOCK_PREFIX_HERE \
  45                 ".pushsection .smp_locks,\"a\"\n"       \
  46                 ".balign 4\n"                           \
  47                 ".long 671f - .\n" /* offset */         \
  48                 ".popsection\n"                         \
  49                 "671:"
  50
  51 #define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock; "
  52
  53 #else /* ! CONFIG_SMP */
  54 #define LOCK_PREFIX_HERE ""
  55 #define LOCK_PREFIX ""
  56 #endif
  57
  58 /*
  59  * The patching flags are part of the upper bits of the @ft_flags parameter when
  60  * specifying them. The split is currently like this:
  61  *
  62  * [31... flags ...16][15... CPUID feature bit ...0]
  63  *
  64  * but since this is all hidden in the macros argument being split, those fields can be
  65  * extended in the future to fit in a u64 or however the need arises.
  66  */
  67 struct alt_instr {
  68         s32 instr_offset;       /* original instruction */
  69         s32 repl_offset;        /* offset to replacement instruction */
  70
  71         union {
  72                 struct {
  73                         u32 cpuid: 16;  /* CPUID bit set for replacement */
  74                         u32 flags: 16;  /* patching control flags */
  75                 };
  76                 u32 ft_flags;
  77         };
  78
  79         u8  instrlen;           /* length of original instruction */
  80         u8  replacementlen;     /* length of new instruction */
  81 } __packed;
  82
  83 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
  84
  85 /*
  86  * Debug flag that can be tested to see whether alternative
  87  * instructions were patched in already:
  88  */
  89 extern int alternatives_patched;
  90 struct module;
  91
  92 extern void alternative_instructions(void);
  93 extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end,
  94                                struct module *mod);
  95 extern void apply_retpolines(s32 *start, s32 *end, struct module *mod);
  96 extern void apply_returns(s32 *start, s32 *end, struct module *mod);
  97 extern void apply_seal_endbr(s32 *start, s32 *end, struct module *mod);
  98 extern void apply_fineibt(s32 *start_retpoline, s32 *end_retpoine,
  99                           s32 *start_cfi, s32 *end_cfi, struct module *mod);
 100
 101 struct callthunk_sites {
 102         s32                             *call_start, *call_end;
 103         struct alt_instr                *alt_start, *alt_end;
 104 };
 105
 106 #ifdef CONFIG_CALL_THUNKS
 107 extern void callthunks_patch_builtin_calls(void);
 108 extern void callthunks_patch_module_calls(struct callthunk_sites *sites,
 109                                           struct module *mod);
 110 extern void *callthunks_translate_call_dest(void *dest);
 111 extern int x86_call_depth_emit_accounting(u8 **pprog, void *func, void *ip);
 112 #else
 113 static __always_inline void callthunks_patch_builtin_calls(void) {}
 114 static __always_inline void
 115 callthunks_patch_module_calls(struct callthunk_sites *sites,
 116                               struct module *mod) {}
 117 static __always_inline void *callthunks_translate_call_dest(void *dest)
 118 {
 119         return dest;
 120 }
 121 static __always_inline int x86_call_depth_emit_accounting(u8 **pprog,
 122                                                           void *func, void *ip)
 123 {
 124         return 0;
 125 }
 126 #endif
 127
 128 #ifdef CONFIG_SMP
 129 extern void alternatives_smp_module_add(struct module *mod, char *name,
 130                                         void *locks, void *locks_end,
 131                                         void *text, void *text_end);
 132 extern void alternatives_smp_module_del(struct module *mod);
 133 extern void alternatives_enable_smp(void);
 134 extern int alternatives_text_reserved(void *start, void *end);
 135 extern bool skip_smp_alternatives;
 136 #else
 137 static inline void alternatives_smp_module_add(struct module *mod, char *name,
 138                                                void *locks, void *locks_end,
 139                                                void *text, void *text_end) {}
 140 static inline void alternatives_smp_module_del(struct module *mod) {}
 141 static inline void alternatives_enable_smp(void) {}
 142 static inline int alternatives_text_reserved(void *start, void *end)
 143 {
 144         return 0;
 145 }
 146 #endif  /* CONFIG_SMP */
 147
 148 #define ALT_CALL_INSTR          "call BUG_func"
 149
 150 #define alt_slen                "772b-771b"
 151 #define alt_total_slen          "773b-771b"
 152 #define alt_rlen                "775f-774f"
 153
 154 #define OLDINSTR(oldinstr)                                              \
 155         "# ALT: oldinstr\n"                                             \
 156         "771:\n\t" oldinstr "\n772:\n"                                  \
 157         "# ALT: padding\n"                                              \
 158         ".skip -(((" alt_rlen ")-(" alt_slen ")) > 0) * "               \
 159                 "((" alt_rlen ")-(" alt_slen ")),0x90\n"                \
 160         "773:\n"
 161
 162 #define ALTINSTR_ENTRY(ft_flags)                                              \
 163         ".pushsection .altinstructions,\"a\"\n"                               \
 164         " .long 771b - .\n"                             /* label           */ \
 165         " .long 774f - .\n"                             /* new instruction */ \
 166         " .4byte " __stringify(ft_flags) "\n"           /* feature + flags */ \
 167         " .byte " alt_total_slen "\n"                   /* source len      */ \
 168         " .byte " alt_rlen "\n"                         /* replacement len */ \
 169         ".popsection\n"
 170
 171 #define ALTINSTR_REPLACEMENT(newinstr)          /* replacement */       \
 172         ".pushsection .altinstr_replacement, \"ax\"\n"                  \
 173         "# ALT: replacement\n"                                          \
 174         "774:\n\t" newinstr "\n775:\n"                                  \
 175         ".popsection\n"
 176
 177 /* alternative assembly primitive: */
 178 #define ALTERNATIVE(oldinstr, newinstr, ft_flags)                       \
 179         OLDINSTR(oldinstr)                                              \
 180         ALTINSTR_ENTRY(ft_flags)                                        \
 181         ALTINSTR_REPLACEMENT(newinstr)
 182
 183 #define ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) \
 184         ALTERNATIVE(ALTERNATIVE(oldinstr, newinstr1, ft_flags1), newinstr2, ft_flags2)
 185
 186 /* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
 187 #define ALTERNATIVE_TERNARY(oldinstr, ft_flags, newinstr_yes, newinstr_no) \
 188         ALTERNATIVE_2(oldinstr, newinstr_no, X86_FEATURE_ALWAYS, newinstr_yes, ft_flags)
 189
 190 #define ALTERNATIVE_3(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2, \
 191                         newinstr3, ft_flags3)                           \
 192         ALTERNATIVE(ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2), \
 193                       newinstr3, ft_flags3)
 194
 195 /*
 196  * Alternative instructions for different CPU types or capabilities.
 197  *
 198  * This allows to use optimized instructions even on generic binary
 199  * kernels.
 200  *
 201  * length of oldinstr must be longer or equal the length of newinstr
 202  * It can be padded with nops as needed.
 203  *
 204  * For non barrier like inlines please define new variants
 205  * without volatile and memory clobber.
 206  */
 207 #define alternative(oldinstr, newinstr, ft_flags)                       \
 208         asm_inline volatile(ALTERNATIVE(oldinstr, newinstr, ft_flags) : : : "memory")
 209
 210 #define alternative_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) \
 211         asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) ::: "memory")
 212
 213 /*
 214  * Alternative inline assembly with input.
 215  *
 216  * Peculiarities:
 217  * No memory clobber here.
 218  * Argument numbers start with 1.
 219  * Leaving an unused argument 0 to keep API compatibility.
 220  */
 221 #define alternative_input(oldinstr, newinstr, ft_flags, input...)       \
 222         asm_inline volatile(ALTERNATIVE(oldinstr, newinstr, ft_flags) \
 223                 : : "i" (0), ## input)
 224
 225 /* Like alternative_input, but with a single output argument */
 226 #define alternative_io(oldinstr, newinstr, ft_flags, output, input...)  \
 227         asm_inline volatile(ALTERNATIVE(oldinstr, newinstr, ft_flags)   \
 228                 : output : "i" (0), ## input)
 229
 230 /*
 231  * Like alternative_io, but for replacing a direct call with another one.
 232  *
 233  * Use the %c operand modifier which is the generic way to print a bare
 234  * constant expression with all syntax-specific punctuation omitted. %P
 235  * is the x86-specific variant which can handle constants too, for
 236  * historical reasons, but it should be used primarily for PIC
 237  * references: i.e., if used for a function, it would add the PLT
 238  * suffix.
 239  */
 240 #define alternative_call(oldfunc, newfunc, ft_flags, output, input...)                  \
 241         asm_inline volatile(ALTERNATIVE("call %c[old]", "call %c[new]", ft_flags)       \
 242                 : ALT_OUTPUT_SP(output)                                                 \
 243                 : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 244
 245 /*
 246  * Like alternative_call, but there are two features and respective functions.
 247  * If CPU has feature2, function2 is used.
 248  * Otherwise, if CPU has feature1, function1 is used.
 249  * Otherwise, old function is used.
 250  */
 251 #define alternative_call_2(oldfunc, newfunc1, ft_flags1, newfunc2, ft_flags2,           \
 252                            output, input...)                                            \
 253         asm_inline volatile(ALTERNATIVE_2("call %c[old]", "call %c[new1]", ft_flags1,   \
 254                 "call %c[new2]", ft_flags2)                                             \
 255                 : ALT_OUTPUT_SP(output)                                                 \
 256                 : [old] "i" (oldfunc), [new1] "i" (newfunc1),                           \
 257                   [new2] "i" (newfunc2), ## input)
 258
 259 /*
 260  * use this macro(s) if you need more than one output parameter
 261  * in alternative_io
 262  */
 263 #define ASM_OUTPUT2(a...) a
 264
 265 /*
 266  * use this macro if you need clobbers but no inputs in
 267  * alternative_{input,io,call}()
 268  */
 269 #define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
 270
 271 #define ALT_OUTPUT_SP(...) ASM_CALL_CONSTRAINT, ## __VA_ARGS__
 272
 273 /* Macro for creating assembler functions avoiding any C magic. */
 274 #define DEFINE_ASM_FUNC(func, instr, sec)               \
 275         asm (".pushsection " #sec ", \"ax\"\n"          \
 276              ".global " #func "\n\t"                    \
 277              ".type " #func ", @function\n\t"           \
 278              ASM_FUNC_ALIGN "\n"                        \
 279              #func ":\n\t"                              \
 280              ASM_ENDBR                                  \
 281              instr "\n\t"                               \
 282              ASM_RET                                    \
 283              ".size " #func ", . - " #func "\n\t"       \
 284              ".popsection")
 285
 286 void BUG_func(void);
 287 void nop_func(void);
 288
 289 #else /* __ASSEMBLY__ */
 290
 291 #ifdef CONFIG_SMP
 292         .macro LOCK_PREFIX
 293 672:    lock
 294         .pushsection .smp_locks,"a"
 295         .balign 4
 296         .long 672b - .
 297         .popsection
 298         .endm
 299 #else
 300         .macro LOCK_PREFIX
 301         .endm
 302 #endif
 303
 304 /*
 305  * Issue one struct alt_instr descriptor entry (need to put it into
 306  * the section .altinstructions, see below). This entry contains
 307  * enough information for the alternatives patching code to patch an
 308  * instruction. See apply_alternatives().
 309  */
 310 .macro altinstr_entry orig alt ft_flags orig_len alt_len
 311         .long \orig - .
 312         .long \alt - .
 313         .4byte \ft_flags
 314         .byte \orig_len
 315         .byte \alt_len
 316 .endm
 317
 318 .macro ALT_CALL_INSTR
 319         call BUG_func
 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 #define __ALTERNATIVE(oldinst, newinst, flag)                           \
 329 740:                                                                    \
 330         oldinst ;                                                       \
 331 741:                                                                    \
 332         .skip -(((744f-743f)-(741b-740b)) > 0) * ((744f-743f)-(741b-740b)),0x90 ;\
 333 742:                                                                    \
 334         .pushsection .altinstructions,"a" ;                             \
 335         altinstr_entry 740b,743f,flag,742b-740b,744f-743f ;             \
 336         .popsection ;                                                   \
 337         .pushsection .altinstr_replacement,"ax" ;                       \
 338 743:                                                                    \
 339         newinst ;                                                       \
 340 744:                                                                    \
 341         .popsection ;
 342
 343 .macro ALTERNATIVE oldinstr, newinstr, ft_flags
 344         __ALTERNATIVE(\oldinstr, \newinstr, \ft_flags)
 345 .endm
 346
 347 #define old_len                 141b-140b
 348 #define new_len1                144f-143f
 349 #define new_len2                145f-144f
 350 #define new_len3                146f-145f
 351
 352 /*
 353  * Same as ALTERNATIVE macro above but for two alternatives. If CPU
 354  * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
 355  * @feature2, it replaces @oldinstr with @feature2.
 356  */
 357 .macro ALTERNATIVE_2 oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2
 358         __ALTERNATIVE(__ALTERNATIVE(\oldinstr, \newinstr1, \ft_flags1),
 359                       \newinstr2, \ft_flags2)
 360 .endm
 361
 362 .macro ALTERNATIVE_3 oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2, newinstr3, ft_flags3
 363         __ALTERNATIVE(ALTERNATIVE_2(\oldinstr, \newinstr1, \ft_flags1, \newinstr2, \ft_flags2),
 364                       \newinstr3, \ft_flags3)
 365 .endm
 366
 367 /* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
 368 #define ALTERNATIVE_TERNARY(oldinstr, ft_flags, newinstr_yes, newinstr_no) \
 369         ALTERNATIVE_2 oldinstr, newinstr_no, X86_FEATURE_ALWAYS,        \
 370         newinstr_yes, ft_flags
 371
 372 #endif /* __ASSEMBLY__ */
 373
 374 #endif /* _ASM_X86_ALTERNATIVE_H */