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#include <asm/bug.h>
10
11#define ALT_FLAGS_SHIFT 16
12
13#define ALT_FLAG_NOT (1 << 0)
14#define ALT_NOT(feature) ((ALT_FLAG_NOT << ALT_FLAGS_SHIFT) | (feature))
15#define ALT_FLAG_DIRECT_CALL (1 << 1)
16#define ALT_DIRECT_CALL(feature) ((ALT_FLAG_DIRECT_CALL << ALT_FLAGS_SHIFT) | (feature))
17#define ALT_CALL_ALWAYS ALT_DIRECT_CALL(X86_FEATURE_ALWAYS)
18
19#ifndef __ASSEMBLER__
20
21#include <linux/stddef.h>
22
23/*
24 * Alternative inline assembly for SMP.
25 *
26 * The LOCK_PREFIX macro defined here replaces the LOCK and
27 * LOCK_PREFIX macros used everywhere in the source tree.
28 *
29 * SMP alternatives use the same data structures as the other
30 * alternatives and the X86_FEATURE_UP flag to indicate the case of a
31 * UP system running a SMP kernel. The existing apply_alternatives()
32 * works fine for patching a SMP kernel for UP.
33 *
34 * The SMP alternative tables can be kept after boot and contain both
35 * UP and SMP versions of the instructions to allow switching back to
36 * SMP at runtime, when hotplugging in a new CPU, which is especially
37 * useful in virtualized environments.
38 *
39 * The very common lock prefix is handled as special case in a
40 * separate table which is a pure address list without replacement ptr
41 * and size information. That keeps the table sizes small.
42 */
43
44#ifdef CONFIG_SMP
45#define LOCK_PREFIX_HERE \
46 ".pushsection .smp_locks,\"a\"\n" \
47 ".balign 4\n" \
48 ".long 671f - .\n" /* offset */ \
49 ".popsection\n" \
50 "671:"
51
52#define LOCK_PREFIX LOCK_PREFIX_HERE "\n\tlock "
53
54#else /* ! CONFIG_SMP */
55#define LOCK_PREFIX_HERE ""
56#define LOCK_PREFIX ""
57#endif
58
59/*
60 * The patching flags are part of the upper bits of the @ft_flags parameter when
61 * specifying them. The split is currently like this:
62 *
63 * [31... flags ...16][15... CPUID feature bit ...0]
64 *
65 * but since this is all hidden in the macros argument being split, those fields can be
66 * extended in the future to fit in a u64 or however the need arises.
67 */
68struct alt_instr {
69 s32 instr_offset; /* original instruction */
70 s32 repl_offset; /* offset to replacement instruction */
71
72 union {
73 struct {
74 u32 cpuid: 16; /* CPUID bit set for replacement */
75 u32 flags: 16; /* patching control flags */
76 };
77 u32 ft_flags;
78 };
79
80 u8 instrlen; /* length of original instruction */
81 u8 replacementlen; /* length of new instruction */
82} __packed;
83
84extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
85
86extern s32 __retpoline_sites[], __retpoline_sites_end[];
87extern s32 __return_sites[], __return_sites_end[];
88extern s32 __cfi_sites[], __cfi_sites_end[];
89extern s32 __ibt_endbr_seal[], __ibt_endbr_seal_end[];
90extern s32 __smp_locks[], __smp_locks_end[];
91
92/*
93 * Debug flag that can be tested to see whether alternative
94 * instructions were patched in already:
95 */
96extern int alternatives_patched;
97
98extern void alternative_instructions(void);
99extern void apply_alternatives(struct alt_instr *start, struct alt_instr *end);
100extern void apply_retpolines(s32 *start, s32 *end);
101extern void apply_returns(s32 *start, s32 *end);
102extern void apply_seal_endbr(s32 *start, s32 *end);
103extern void apply_fineibt(s32 *start_retpoline, s32 *end_retpoine,
104 s32 *start_cfi, s32 *end_cfi);
105
106struct module;
107
108struct callthunk_sites {
109 s32 *call_start, *call_end;
110};
111
112#ifdef CONFIG_CALL_THUNKS
113extern void callthunks_patch_builtin_calls(void);
114extern void callthunks_patch_module_calls(struct callthunk_sites *sites,
115 struct module *mod);
116extern void *callthunks_translate_call_dest(void *dest);
117extern int x86_call_depth_emit_accounting(u8 **pprog, void *func, void *ip);
118#else
119static __always_inline void callthunks_patch_builtin_calls(void) {}
120static __always_inline void
121callthunks_patch_module_calls(struct callthunk_sites *sites,
122 struct module *mod) {}
123static __always_inline void *callthunks_translate_call_dest(void *dest)
124{
125 return dest;
126}
127static __always_inline int x86_call_depth_emit_accounting(u8 **pprog,
128 void *func, void *ip)
129{
130 return 0;
131}
132#endif
133
134#ifdef CONFIG_MITIGATION_ITS
135extern void its_init_mod(struct module *mod);
136extern void its_fini_mod(struct module *mod);
137extern void its_free_mod(struct module *mod);
138extern u8 *its_static_thunk(int reg);
139#else /* CONFIG_MITIGATION_ITS */
140static inline void its_init_mod(struct module *mod) { }
141static inline void its_fini_mod(struct module *mod) { }
142static inline void its_free_mod(struct module *mod) { }
143static inline u8 *its_static_thunk(int reg)
144{
145 WARN_ONCE(1, "ITS not compiled in");
146
147 return NULL;
148}
149#endif
150
151#if defined(CONFIG_MITIGATION_RETHUNK) && defined(CONFIG_OBJTOOL)
152extern bool cpu_wants_rethunk(void);
153extern bool cpu_wants_rethunk_at(void *addr);
154#else
155static __always_inline bool cpu_wants_rethunk(void)
156{
157 return false;
158}
159static __always_inline bool cpu_wants_rethunk_at(void *addr)
160{
161 return false;
162}
163#endif
164
165#ifdef CONFIG_SMP
166extern void alternatives_smp_module_add(struct module *mod, char *name,
167 void *locks, void *locks_end,
168 void *text, void *text_end);
169extern void alternatives_smp_module_del(struct module *mod);
170extern void alternatives_enable_smp(void);
171extern int alternatives_text_reserved(void *start, void *end);
172extern bool skip_smp_alternatives;
173#else
174static inline void alternatives_smp_module_add(struct module *mod, char *name,
175 void *locks, void *locks_end,
176 void *text, void *text_end) {}
177static inline void alternatives_smp_module_del(struct module *mod) {}
178static inline void alternatives_enable_smp(void) {}
179static inline int alternatives_text_reserved(void *start, void *end)
180{
181 return 0;
182}
183#endif /* CONFIG_SMP */
184
185#define ALT_CALL_INSTR "call BUG_func"
186
187#define alt_slen "772b-771b"
188#define alt_total_slen "773b-771b"
189#define alt_rlen "775f-774f"
190
191#define OLDINSTR(oldinstr) \
192 "# ALT: oldinstr\n" \
193 "771:\n\t" oldinstr "\n772:\n" \
194 "# ALT: padding\n" \
195 ".skip -(((" alt_rlen ")-(" alt_slen ")) > 0) * " \
196 "((" alt_rlen ")-(" alt_slen ")),0x90\n" \
197 "773:\n"
198
199#define ALTINSTR_ENTRY(ft_flags) \
200 ".pushsection .altinstructions,\"a\"\n" \
201 " .long 771b - .\n" /* label */ \
202 " .long 774f - .\n" /* new instruction */ \
203 " .4byte " __stringify(ft_flags) "\n" /* feature + flags */ \
204 " .byte " alt_total_slen "\n" /* source len */ \
205 " .byte " alt_rlen "\n" /* replacement len */ \
206 ".popsection\n"
207
208#define ALTINSTR_REPLACEMENT(newinstr) /* replacement */ \
209 ".pushsection .altinstr_replacement, \"ax\"\n" \
210 "# ALT: replacement\n" \
211 "774:\n\t" newinstr "\n775:\n" \
212 ".popsection\n"
213
214/* alternative assembly primitive: */
215#define ALTERNATIVE(oldinstr, newinstr, ft_flags) \
216 OLDINSTR(oldinstr) \
217 ALTINSTR_ENTRY(ft_flags) \
218 ALTINSTR_REPLACEMENT(newinstr)
219
220#define ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) \
221 ALTERNATIVE(ALTERNATIVE(oldinstr, newinstr1, ft_flags1), newinstr2, ft_flags2)
222
223/* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
224#define ALTERNATIVE_TERNARY(oldinstr, ft_flags, newinstr_yes, newinstr_no) \
225 ALTERNATIVE_2(oldinstr, newinstr_no, X86_FEATURE_ALWAYS, newinstr_yes, ft_flags)
226
227#define ALTERNATIVE_3(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2, \
228 newinstr3, ft_flags3) \
229 ALTERNATIVE(ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2), \
230 newinstr3, ft_flags3)
231
232/*
233 * Alternative instructions for different CPU types or capabilities.
234 *
235 * This allows to use optimized instructions even on generic binary
236 * kernels.
237 *
238 * length of oldinstr must be longer or equal the length of newinstr
239 * It can be padded with nops as needed.
240 *
241 * For non barrier like inlines please define new variants
242 * without volatile and memory clobber.
243 */
244#define alternative(oldinstr, newinstr, ft_flags) \
245 asm_inline volatile(ALTERNATIVE(oldinstr, newinstr, ft_flags) : : : "memory")
246
247#define alternative_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) \
248 asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) ::: "memory")
249
250/*
251 * Alternative inline assembly with input.
252 *
253 * Peculiarities:
254 * No memory clobber here.
255 * Argument numbers start with 1.
256 * Leaving an unused argument 0 to keep API compatibility.
257 */
258#define alternative_input(oldinstr, newinstr, ft_flags, input...) \
259 asm_inline volatile(ALTERNATIVE(oldinstr, newinstr, ft_flags) \
260 : : "i" (0), ## input)
261
262/* Like alternative_input, but with a single output argument */
263#define alternative_io(oldinstr, newinstr, ft_flags, output, input...) \
264 asm_inline volatile(ALTERNATIVE(oldinstr, newinstr, ft_flags) \
265 : output : "i" (0), ## input)
266
267/*
268 * Like alternative_io, but for replacing a direct call with another one.
269 *
270 * Use the %c operand modifier which is the generic way to print a bare
271 * constant expression with all syntax-specific punctuation omitted. %P
272 * is the x86-specific variant which can handle constants too, for
273 * historical reasons, but it should be used primarily for PIC
274 * references: i.e., if used for a function, it would add the PLT
275 * suffix.
276 */
277#define alternative_call(oldfunc, newfunc, ft_flags, output, input, clobbers...) \
278 asm_inline volatile(ALTERNATIVE("call %c[old]", "call %c[new]", ft_flags) \
279 : ALT_OUTPUT_SP(output) \
280 : [old] "i" (oldfunc), [new] "i" (newfunc) \
281 COMMA(input) \
282 : clobbers)
283
284/*
285 * Like alternative_call, but there are two features and respective functions.
286 * If CPU has feature2, function2 is used.
287 * Otherwise, if CPU has feature1, function1 is used.
288 * Otherwise, old function is used.
289 */
290#define alternative_call_2(oldfunc, newfunc1, ft_flags1, newfunc2, ft_flags2, \
291 output, input, clobbers...) \
292 asm_inline volatile(ALTERNATIVE_2("call %c[old]", "call %c[new1]", ft_flags1, \
293 "call %c[new2]", ft_flags2) \
294 : ALT_OUTPUT_SP(output) \
295 : [old] "i" (oldfunc), [new1] "i" (newfunc1), \
296 [new2] "i" (newfunc2) \
297 COMMA(input) \
298 : clobbers)
299
300#define ALT_OUTPUT_SP(...) ASM_CALL_CONSTRAINT, ## __VA_ARGS__
301
302/* Macro for creating assembler functions avoiding any C magic. */
303#define DEFINE_ASM_FUNC(func, instr, sec) \
304 asm (".pushsection " #sec ", \"ax\"\n" \
305 ".global " #func "\n\t" \
306 ".type " #func ", @function\n\t" \
307 ASM_FUNC_ALIGN "\n" \
308 #func ":\n\t" \
309 ASM_ENDBR \
310 instr "\n\t" \
311 ASM_RET \
312 ".size " #func ", . - " #func "\n\t" \
313 ".popsection")
314
315void BUG_func(void);
316void nop_func(void);
317
318#else /* __ASSEMBLER__ */
319
320#ifdef CONFIG_SMP
321 .macro LOCK_PREFIX
322672: lock
323 .pushsection .smp_locks,"a"
324 .balign 4
325 .long 672b - .
326 .popsection
327 .endm
328#else
329 .macro LOCK_PREFIX
330 .endm
331#endif
332
333/*
334 * Issue one struct alt_instr descriptor entry (need to put it into
335 * the section .altinstructions, see below). This entry contains
336 * enough information for the alternatives patching code to patch an
337 * instruction. See apply_alternatives().
338 */
339.macro altinstr_entry orig alt ft_flags orig_len alt_len
340 .long \orig - .
341 .long \alt - .
342 .4byte \ft_flags
343 .byte \orig_len
344 .byte \alt_len
345.endm
346
347.macro ALT_CALL_INSTR
348 call BUG_func
349.endm
350
351/*
352 * Define an alternative between two instructions. If @feature is
353 * present, early code in apply_alternatives() replaces @oldinstr with
354 * @newinstr. ".skip" directive takes care of proper instruction padding
355 * in case @newinstr is longer than @oldinstr.
356 */
357#define __ALTERNATIVE(oldinst, newinst, flag) \
358740: \
359 oldinst ; \
360741: \
361 .skip -(((744f-743f)-(741b-740b)) > 0) * ((744f-743f)-(741b-740b)),0x90 ;\
362742: \
363 .pushsection .altinstructions,"a" ; \
364 altinstr_entry 740b,743f,flag,742b-740b,744f-743f ; \
365 .popsection ; \
366 .pushsection .altinstr_replacement,"ax" ; \
367743: \
368 newinst ; \
369744: \
370 .popsection ;
371
372.macro ALTERNATIVE oldinstr, newinstr, ft_flags
373 __ALTERNATIVE(\oldinstr, \newinstr, \ft_flags)
374.endm
375
376/*
377 * Same as ALTERNATIVE macro above but for two alternatives. If CPU
378 * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
379 * @feature2, it replaces @oldinstr with @feature2.
380 */
381.macro ALTERNATIVE_2 oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2
382 __ALTERNATIVE(__ALTERNATIVE(\oldinstr, \newinstr1, \ft_flags1),
383 \newinstr2, \ft_flags2)
384.endm
385
386.macro ALTERNATIVE_3 oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2, newinstr3, ft_flags3
387 __ALTERNATIVE(ALTERNATIVE_2(\oldinstr, \newinstr1, \ft_flags1, \newinstr2, \ft_flags2),
388 \newinstr3, \ft_flags3)
389.endm
390
391/* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
392#define ALTERNATIVE_TERNARY(oldinstr, ft_flags, newinstr_yes, newinstr_no) \
393 ALTERNATIVE_2 oldinstr, newinstr_no, X86_FEATURE_ALWAYS, \
394 newinstr_yes, ft_flags
395
396#endif /* __ASSEMBLER__ */
397
398#endif /* _ASM_X86_ALTERNATIVE_H */
399

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