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
62struct 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 */
74extern int alternatives_patched;
75
76extern void alternative_instructions(void);
77extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
78extern void apply_retpolines(s32 *start, s32 *end);
79extern void apply_returns(s32 *start, s32 *end);
80extern void apply_ibt_endbr(s32 *start, s32 *end);
81
82struct module;
83
84#ifdef CONFIG_SMP
85extern void alternatives_smp_module_add(struct module *mod, char *name,
86 void *locks, void *locks_end,
87 void *text, void *text_end);
88extern void alternatives_smp_module_del(struct module *mod);
89extern void alternatives_enable_smp(void);
90extern int alternatives_text_reserved(void *start, void *end);
91extern bool skip_smp_alternatives;
92#else
93static inline void alternatives_smp_module_add(struct module *mod, char *name,
94 void *locks, void *locks_end,
95 void *text, void *text_end) {}
96static inline void alternatives_smp_module_del(struct module *mod) {}
97static inline void alternatives_enable_smp(void) {}
98static inline int alternatives_text_reserved(void *start, void *end)
99{
100 return 0;
101}
102#endif /* CONFIG_SMP */
103
104#define b_replacement(num) "664"#num
105#define e_replacement(num) "665"#num
106
107#define alt_end_marker "663"
108#define alt_slen "662b-661b"
109#define alt_total_slen alt_end_marker"b-661b"
110#define alt_rlen(num) e_replacement(num)"f-"b_replacement(num)"f"
111
112#define OLDINSTR(oldinstr, num) \
113 "# ALT: oldnstr\n" \
114 "661:\n\t" oldinstr "\n662:\n" \
115 "# ALT: padding\n" \
116 ".skip -(((" alt_rlen(num) ")-(" alt_slen ")) > 0) * " \
117 "((" alt_rlen(num) ")-(" alt_slen ")),0x90\n" \
118 alt_end_marker ":\n"
119
120/*
121 * gas compatible max based on the idea from:
122 * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
123 *
124 * The additional "-" is needed because gas uses a "true" value of -1.
125 */
126#define alt_max_short(a, b) "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") < (" b ")))))"
127
128/*
129 * Pad the second replacement alternative with additional NOPs if it is
130 * additionally longer than the first replacement alternative.
131 */
132#define OLDINSTR_2(oldinstr, num1, num2) \
133 "# ALT: oldinstr2\n" \
134 "661:\n\t" oldinstr "\n662:\n" \
135 "# ALT: padding2\n" \
136 ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * " \
137 "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n" \
138 alt_end_marker ":\n"
139
140#define OLDINSTR_3(oldinsn, n1, n2, n3) \
141 "# ALT: oldinstr3\n" \
142 "661:\n\t" oldinsn "\n662:\n" \
143 "# ALT: padding3\n" \
144 ".skip -((" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3)) \
145 " - (" alt_slen ")) > 0) * " \
146 "(" alt_max_short(alt_max_short(alt_rlen(n1), alt_rlen(n2)), alt_rlen(n3)) \
147 " - (" alt_slen ")), 0x90\n" \
148 alt_end_marker ":\n"
149
150#define ALTINSTR_ENTRY(feature, num) \
151 " .long 661b - .\n" /* label */ \
152 " .long " b_replacement(num)"f - .\n" /* new instruction */ \
153 " .word " __stringify(feature) "\n" /* feature bit */ \
154 " .byte " alt_total_slen "\n" /* source len */ \
155 " .byte " alt_rlen(num) "\n" /* replacement len */
156
157#define ALTINSTR_REPLACEMENT(newinstr, num) /* replacement */ \
158 "# ALT: replacement " #num "\n" \
159 b_replacement(num)":\n\t" newinstr "\n" e_replacement(num) ":\n"
160
161/* alternative assembly primitive: */
162#define ALTERNATIVE(oldinstr, newinstr, feature) \
163 OLDINSTR(oldinstr, 1) \
164 ".pushsection .altinstructions,\"a\"\n" \
165 ALTINSTR_ENTRY(feature, 1) \
166 ".popsection\n" \
167 ".pushsection .altinstr_replacement, \"ax\"\n" \
168 ALTINSTR_REPLACEMENT(newinstr, 1) \
169 ".popsection\n"
170
171#define ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2)\
172 OLDINSTR_2(oldinstr, 1, 2) \
173 ".pushsection .altinstructions,\"a\"\n" \
174 ALTINSTR_ENTRY(feature1, 1) \
175 ALTINSTR_ENTRY(feature2, 2) \
176 ".popsection\n" \
177 ".pushsection .altinstr_replacement, \"ax\"\n" \
178 ALTINSTR_REPLACEMENT(newinstr1, 1) \
179 ALTINSTR_REPLACEMENT(newinstr2, 2) \
180 ".popsection\n"
181
182/* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
183#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr_yes, newinstr_no) \
184 ALTERNATIVE_2(oldinstr, newinstr_no, X86_FEATURE_ALWAYS, \
185 newinstr_yes, feature)
186
187#define ALTERNATIVE_3(oldinsn, newinsn1, feat1, newinsn2, feat2, newinsn3, feat3) \
188 OLDINSTR_3(oldinsn, 1, 2, 3) \
189 ".pushsection .altinstructions,\"a\"\n" \
190 ALTINSTR_ENTRY(feat1, 1) \
191 ALTINSTR_ENTRY(feat2, 2) \
192 ALTINSTR_ENTRY(feat3, 3) \
193 ".popsection\n" \
194 ".pushsection .altinstr_replacement, \"ax\"\n" \
195 ALTINSTR_REPLACEMENT(newinsn1, 1) \
196 ALTINSTR_REPLACEMENT(newinsn2, 2) \
197 ALTINSTR_REPLACEMENT(newinsn3, 3) \
198 ".popsection\n"
199
200/*
201 * Alternative instructions for different CPU types or capabilities.
202 *
203 * This allows to use optimized instructions even on generic binary
204 * kernels.
205 *
206 * length of oldinstr must be longer or equal the length of newinstr
207 * It can be padded with nops as needed.
208 *
209 * For non barrier like inlines please define new variants
210 * without volatile and memory clobber.
211 */
212#define alternative(oldinstr, newinstr, feature) \
213 asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature) : : : "memory")
214
215#define alternative_2(oldinstr, newinstr1, feature1, newinstr2, feature2) \
216 asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, newinstr2, feature2) ::: "memory")
217
218#define alternative_ternary(oldinstr, feature, newinstr_yes, newinstr_no) \
219 asm_inline volatile(ALTERNATIVE_TERNARY(oldinstr, feature, newinstr_yes, newinstr_no) ::: "memory")
220
221/*
222 * Alternative inline assembly with input.
223 *
224 * Peculiarities:
225 * No memory clobber here.
226 * Argument numbers start with 1.
227 * Leaving an unused argument 0 to keep API compatibility.
228 */
229#define alternative_input(oldinstr, newinstr, feature, input...) \
230 asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
231 : : "i" (0), ## input)
232
233/*
234 * This is similar to alternative_input. But it has two features and
235 * respective instructions.
236 *
237 * If CPU has feature2, newinstr2 is used.
238 * Otherwise, if CPU has feature1, newinstr1 is used.
239 * Otherwise, oldinstr is used.
240 */
241#define alternative_input_2(oldinstr, newinstr1, feature1, newinstr2, \
242 feature2, input...) \
243 asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, feature1, \
244 newinstr2, feature2) \
245 : : "i" (0), ## input)
246
247/* Like alternative_input, but with a single output argument */
248#define alternative_io(oldinstr, newinstr, feature, output, input...) \
249 asm_inline volatile (ALTERNATIVE(oldinstr, newinstr, feature) \
250 : output : "i" (0), ## input)
251
252/* Like alternative_io, but for replacing a direct call with another one. */
253#define alternative_call(oldfunc, newfunc, feature, output, input...) \
254 asm_inline volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
255 : output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
256
257/*
258 * Like alternative_call, but there are two features and respective functions.
259 * If CPU has feature2, function2 is used.
260 * Otherwise, if CPU has feature1, function1 is used.
261 * Otherwise, old function is used.
262 */
263#define alternative_call_2(oldfunc, newfunc1, feature1, newfunc2, feature2, \
264 output, input...) \
265 asm_inline volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
266 "call %P[new2]", feature2) \
267 : output, ASM_CALL_CONSTRAINT \
268 : [old] "i" (oldfunc), [new1] "i" (newfunc1), \
269 [new2] "i" (newfunc2), ## input)
270
271/*
272 * use this macro(s) if you need more than one output parameter
273 * in alternative_io
274 */
275#define ASM_OUTPUT2(a...) a
276
277/*
278 * use this macro if you need clobbers but no inputs in
279 * alternative_{input,io,call}()
280 */
281#define ASM_NO_INPUT_CLOBBER(clbr...) "i" (0) : clbr
282
283#else /* __ASSEMBLY__ */
284
285#ifdef CONFIG_SMP
286 .macro LOCK_PREFIX
287672: lock
288 .pushsection .smp_locks,"a"
289 .balign 4
290 .long 672b - .
291 .popsection
292 .endm
293#else
294 .macro LOCK_PREFIX
295 .endm
296#endif
297
298/*
299 * objtool annotation to ignore the alternatives and only consider the original
300 * instruction(s).
301 */
302.macro ANNOTATE_IGNORE_ALTERNATIVE
303 .Lannotate_\@:
304 .pushsection .discard.ignore_alts
305 .long .Lannotate_\@ - .
306 .popsection
307.endm
308
309/*
310 * Issue one struct alt_instr descriptor entry (need to put it into
311 * the section .altinstructions, see below). This entry contains
312 * enough information for the alternatives patching code to patch an
313 * instruction. See apply_alternatives().
314 */
315.macro altinstruction_entry orig alt feature orig_len alt_len
316 .long \orig - .
317 .long \alt - .
318 .word \feature
319 .byte \orig_len
320 .byte \alt_len
321.endm
322
323/*
324 * Define an alternative between two instructions. If @feature is
325 * present, early code in apply_alternatives() replaces @oldinstr with
326 * @newinstr. ".skip" directive takes care of proper instruction padding
327 * in case @newinstr is longer than @oldinstr.
328 */
329.macro ALTERNATIVE oldinstr, newinstr, feature
330140:
331 \oldinstr
332141:
333 .skip -(((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)),0x90
334142:
335
336 .pushsection .altinstructions,"a"
337 altinstruction_entry 140b,143f,\feature,142b-140b,144f-143f
338 .popsection
339
340 .pushsection .altinstr_replacement,"ax"
341143:
342 \newinstr
343144:
344 .popsection
345.endm
346
347#define old_len 141b-140b
348#define new_len1 144f-143f
349#define new_len2 145f-144f
350
351/*
352 * gas compatible max based on the idea from:
353 * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax
354 *
355 * The additional "-" is needed because gas uses a "true" value of -1.
356 */
357#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b)))))
358
359
360/*
361 * Same as ALTERNATIVE macro above but for two alternatives. If CPU
362 * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
363 * @feature2, it replaces @oldinstr with @feature2.
364 */
365.macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2
366140:
367 \oldinstr
368141:
369 .skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \
370 (alt_max_short(new_len1, new_len2) - (old_len)),0x90
371142:
372
373 .pushsection .altinstructions,"a"
374 altinstruction_entry 140b,143f,\feature1,142b-140b,144f-143f
375 altinstruction_entry 140b,144f,\feature2,142b-140b,145f-144f
376 .popsection
377
378 .pushsection .altinstr_replacement,"ax"
379143:
380 \newinstr1
381144:
382 \newinstr2
383145:
384 .popsection
385.endm
386
387/* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
388#define ALTERNATIVE_TERNARY(oldinstr, feature, newinstr_yes, newinstr_no) \
389 ALTERNATIVE_2 oldinstr, newinstr_no, X86_FEATURE_ALWAYS, \
390 newinstr_yes, feature
391
392#endif /* __ASSEMBLY__ */
393
394#endif /* _ASM_X86_ALTERNATIVE_H */
395

source code of linux/arch/x86/include/asm/alternative.h