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#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, \"aM\", @progbits, "		      \
201		      __stringify(ALT_INSTR_SIZE) "\n"			      \
202	" .long 771b - .\n"				/* label           */ \
203	" .long 774f - .\n"				/* new instruction */ \
204	" .4byte " __stringify(ft_flags) "\n"		/* feature + flags */ \
205	" .byte " alt_total_slen "\n"			/* source len      */ \
206	" .byte " alt_rlen "\n"				/* replacement len */ \
207	".popsection\n"
208
209#define ALTINSTR_REPLACEMENT(newinstr)		/* replacement */	\
210	".pushsection .altinstr_replacement, \"ax\"\n"			\
211	ANNOTATE_DATA_SPECIAL "\n"					\
212	"# ALT: replacement\n"						\
213	"774:\n\t" newinstr "\n775:\n"					\
214	".popsection\n"
215
216/* alternative assembly primitive: */
217#define ALTERNATIVE(oldinstr, newinstr, ft_flags)			\
218	OLDINSTR(oldinstr)						\
219	ALTINSTR_ENTRY(ft_flags)					\
220	ALTINSTR_REPLACEMENT(newinstr)
221
222#define ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) \
223	ALTERNATIVE(ALTERNATIVE(oldinstr, newinstr1, ft_flags1), newinstr2, ft_flags2)
224
225/* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
226#define ALTERNATIVE_TERNARY(oldinstr, ft_flags, newinstr_yes, newinstr_no) \
227	ALTERNATIVE_2(oldinstr, newinstr_no, X86_FEATURE_ALWAYS, newinstr_yes, ft_flags)
228
229#define ALTERNATIVE_3(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2, \
230			newinstr3, ft_flags3)				\
231	ALTERNATIVE(ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2), \
232		      newinstr3, ft_flags3)
233
234/*
235 * Alternative instructions for different CPU types or capabilities.
236 *
237 * This allows to use optimized instructions even on generic binary
238 * kernels.
239 *
240 * length of oldinstr must be longer or equal the length of newinstr
241 * It can be padded with nops as needed.
242 *
243 * For non barrier like inlines please define new variants
244 * without volatile and memory clobber.
245 */
246#define alternative(oldinstr, newinstr, ft_flags)			\
247	asm_inline volatile(ALTERNATIVE(oldinstr, newinstr, ft_flags) : : : "memory")
248
249#define alternative_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) \
250	asm_inline volatile(ALTERNATIVE_2(oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2) ::: "memory")
251
252/*
253 * Alternative inline assembly with input.
254 *
255 * Peculiarities:
256 * No memory clobber here.
257 * Argument numbers start with 1.
258 * Leaving an unused argument 0 to keep API compatibility.
259 */
260#define alternative_input(oldinstr, newinstr, ft_flags, input...)	\
261	asm_inline volatile(ALTERNATIVE(oldinstr, newinstr, ft_flags) \
262		: : "i" (0), ## input)
263
264/* Like alternative_input, but with a single output argument */
265#define alternative_io(oldinstr, newinstr, ft_flags, output, input...)	\
266	asm_inline volatile(ALTERNATIVE(oldinstr, newinstr, ft_flags)	\
267		: output : "i" (0), ## input)
268
269/*
270 * Like alternative_io, but for replacing a direct call with another one.
271 *
272 * Use the %c operand modifier which is the generic way to print a bare
273 * constant expression with all syntax-specific punctuation omitted. %P
274 * is the x86-specific variant which can handle constants too, for
275 * historical reasons, but it should be used primarily for PIC
276 * references: i.e., if used for a function, it would add the PLT
277 * suffix.
278 */
279#define alternative_call(oldfunc, newfunc, ft_flags, output, input, clobbers...)	\
280	asm_inline volatile(ALTERNATIVE("call %c[old]", "call %c[new]", ft_flags)	\
281		: ALT_OUTPUT_SP(output)							\
282		: [old] "i" (oldfunc), [new] "i" (newfunc)				\
283		  COMMA(input)								\
284		: clobbers)
285
286/*
287 * Like alternative_call, but there are two features and respective functions.
288 * If CPU has feature2, function2 is used.
289 * Otherwise, if CPU has feature1, function1 is used.
290 * Otherwise, old function is used.
291 */
292#define alternative_call_2(oldfunc, newfunc1, ft_flags1, newfunc2, ft_flags2,		\
293			   output, input, clobbers...)					\
294	asm_inline volatile(ALTERNATIVE_2("call %c[old]", "call %c[new1]", ft_flags1,	\
295		"call %c[new2]", ft_flags2)						\
296		: ALT_OUTPUT_SP(output)							\
297		: [old] "i" (oldfunc), [new1] "i" (newfunc1),				\
298		  [new2] "i" (newfunc2)							\
299		  COMMA(input)								\
300		: clobbers)
301
302#define ALT_OUTPUT_SP(...) ASM_CALL_CONSTRAINT, ## __VA_ARGS__
303
304/* Macro for creating assembler functions avoiding any C magic. */
305#define DEFINE_ASM_FUNC(func, instr, sec)		\
306	asm (".pushsection " #sec ", \"ax\"\n"		\
307	     ".global " #func "\n\t"			\
308	     ".type " #func ", @function\n\t"		\
309	     ASM_FUNC_ALIGN "\n"			\
310	     #func ":\n\t"				\
311	     ASM_ENDBR					\
312	     instr "\n\t"				\
313	     ASM_RET					\
314	     ".size " #func ", . - " #func "\n\t"	\
315	     ".popsection")
316
317void BUG_func(void);
318void nop_func(void);
319
320#else /* __ASSEMBLER__ */
321
322#ifdef CONFIG_SMP
323	.macro LOCK_PREFIX
324672:	lock
325	.pushsection .smp_locks,"a"
326	.balign 4
327	.long 672b - .
328	.popsection
329	.endm
330#else
331	.macro LOCK_PREFIX
332	.endm
333#endif
334
335/*
336 * Issue one struct alt_instr descriptor entry (need to put it into
337 * the section .altinstructions, see below). This entry contains
338 * enough information for the alternatives patching code to patch an
339 * instruction. See apply_alternatives().
340 */
341.macro altinstr_entry orig alt ft_flags orig_len alt_len
342	.long \orig - .
343	.long \alt - .
344	.4byte \ft_flags
345	.byte \orig_len
346	.byte \alt_len
347.endm
348
349.macro ALT_CALL_INSTR
350	call BUG_func
351.endm
352
353/*
354 * Define an alternative between two instructions. If @feature is
355 * present, early code in apply_alternatives() replaces @oldinstr with
356 * @newinstr. ".skip" directive takes care of proper instruction padding
357 * in case @newinstr is longer than @oldinstr.
358 */
359#define __ALTERNATIVE(oldinst, newinst, flag)				\
360740:									\
361	oldinst	;							\
362741:									\
363	.skip -(((744f-743f)-(741b-740b)) > 0) * ((744f-743f)-(741b-740b)),0x90	;\
364742:									\
365	.pushsection .altinstructions, "aM", @progbits, ALT_INSTR_SIZE ;\
366	altinstr_entry 740b,743f,flag,742b-740b,744f-743f ;		\
367	.popsection ;							\
368	.pushsection .altinstr_replacement,"ax"	;			\
369743:									\
370	ANNOTATE_DATA_SPECIAL ;						\
371	newinst	;							\
372744:									\
373	.popsection ;
374
375.macro ALTERNATIVE oldinstr, newinstr, ft_flags
376	__ALTERNATIVE(\oldinstr, \newinstr, \ft_flags)
377.endm
378
379/*
380 * Same as ALTERNATIVE macro above but for two alternatives. If CPU
381 * has @feature1, it replaces @oldinstr with @newinstr1. If CPU has
382 * @feature2, it replaces @oldinstr with @feature2.
383 */
384.macro ALTERNATIVE_2 oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2
385	__ALTERNATIVE(__ALTERNATIVE(\oldinstr, \newinstr1, \ft_flags1),
386		      \newinstr2, \ft_flags2)
387.endm
388
389.macro ALTERNATIVE_3 oldinstr, newinstr1, ft_flags1, newinstr2, ft_flags2, newinstr3, ft_flags3
390	__ALTERNATIVE(ALTERNATIVE_2(\oldinstr, \newinstr1, \ft_flags1, \newinstr2, \ft_flags2),
391		      \newinstr3, \ft_flags3)
392.endm
393
394/* If @feature is set, patch in @newinstr_yes, otherwise @newinstr_no. */
395#define ALTERNATIVE_TERNARY(oldinstr, ft_flags, newinstr_yes, newinstr_no) \
396	ALTERNATIVE_2 oldinstr, newinstr_no, X86_FEATURE_ALWAYS,	\
397	newinstr_yes, ft_flags
398
399#endif /* __ASSEMBLER__ */
400
401#endif /* _ASM_X86_ALTERNATIVE_H */