1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef __ASM_ALTERNATIVE_H
3 #define __ASM_ALTERNATIVE_H
4 
5 #include <asm/cpucaps.h>
6 #include <asm/insn.h>
7 
8 #define ARM64_CB_PATCH ARM64_NCAPS
9 
10 #ifndef __ASSEMBLY__
11 
12 #include <linux/init.h>
13 #include <linux/types.h>
14 #include <linux/stddef.h>
15 #include <linux/stringify.h>
16 
17 struct alt_instr {
18 	s32 orig_offset;	/* offset to original instruction */
19 	s32 alt_offset;		/* offset to replacement instruction */
20 	u16 cpufeature;		/* cpufeature bit set for replacement */
21 	u8  orig_len;		/* size of original instruction(s) */
22 	u8  alt_len;		/* size of new instruction(s), <= orig_len */
23 };
24 
25 typedef void (*alternative_cb_t)(struct alt_instr *alt,
26 				 __le32 *origptr, __le32 *updptr, int nr_inst);
27 
28 void __init apply_boot_alternatives(void);
29 void __init apply_alternatives_all(void);
30 bool alternative_is_applied(u16 cpufeature);
31 
32 #ifdef CONFIG_MODULES
33 void apply_alternatives_module(void *start, size_t length);
34 #else
35 static inline void apply_alternatives_module(void *start, size_t length) { }
36 #endif
37 
38 #define ALTINSTR_ENTRY(feature)					              \
39 	" .word 661b - .\n"				/* label           */ \
40 	" .word 663f - .\n"				/* new instruction */ \
41 	" .hword " __stringify(feature) "\n"		/* feature bit     */ \
42 	" .byte 662b-661b\n"				/* source len      */ \
43 	" .byte 664f-663f\n"				/* replacement len */
44 
45 #define ALTINSTR_ENTRY_CB(feature, cb)					      \
46 	" .word 661b - .\n"				/* label           */ \
47 	" .word " __stringify(cb) "- .\n"		/* callback */	      \
48 	" .hword " __stringify(feature) "\n"		/* feature bit     */ \
49 	" .byte 662b-661b\n"				/* source len      */ \
50 	" .byte 664f-663f\n"				/* replacement len */
51 
52 /*
53  * alternative assembly primitive:
54  *
55  * If any of these .org directive fail, it means that insn1 and insn2
56  * don't have the same length. This used to be written as
57  *
58  * .if ((664b-663b) != (662b-661b))
59  * 	.error "Alternatives instruction length mismatch"
60  * .endif
61  *
62  * but most assemblers die if insn1 or insn2 have a .inst. This should
63  * be fixed in a binutils release posterior to 2.25.51.0.2 (anything
64  * containing commit 4e4d08cf7399b606 or c1baaddf8861).
65  *
66  * Alternatives with callbacks do not generate replacement instructions.
67  */
68 #define __ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg_enabled)	\
69 	".if "__stringify(cfg_enabled)" == 1\n"				\
70 	"661:\n\t"							\
71 	oldinstr "\n"							\
72 	"662:\n"							\
73 	".pushsection .altinstructions,\"a\"\n"				\
74 	ALTINSTR_ENTRY(feature)						\
75 	".popsection\n"							\
76 	".subsection 1\n"						\
77 	"663:\n\t"							\
78 	newinstr "\n"							\
79 	"664:\n\t"							\
80 	".org	. - (664b-663b) + (662b-661b)\n\t"			\
81 	".org	. - (662b-661b) + (664b-663b)\n\t"			\
82 	".previous\n"							\
83 	".endif\n"
84 
85 #define __ALTERNATIVE_CFG_CB(oldinstr, feature, cfg_enabled, cb)	\
86 	".if "__stringify(cfg_enabled)" == 1\n"				\
87 	"661:\n\t"							\
88 	oldinstr "\n"							\
89 	"662:\n"							\
90 	".pushsection .altinstructions,\"a\"\n"				\
91 	ALTINSTR_ENTRY_CB(feature, cb)					\
92 	".popsection\n"							\
93 	"663:\n\t"							\
94 	"664:\n\t"							\
95 	".endif\n"
96 
97 #define _ALTERNATIVE_CFG(oldinstr, newinstr, feature, cfg, ...)	\
98 	__ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg))
99 
100 #define ALTERNATIVE_CB(oldinstr, cb) \
101 	__ALTERNATIVE_CFG_CB(oldinstr, ARM64_CB_PATCH, 1, cb)
102 #else
103 
104 #include <asm/assembler.h>
105 
106 .macro altinstruction_entry orig_offset alt_offset feature orig_len alt_len
107 	.word \orig_offset - .
108 	.word \alt_offset - .
109 	.hword \feature
110 	.byte \orig_len
111 	.byte \alt_len
112 .endm
113 
114 .macro alternative_insn insn1, insn2, cap, enable = 1
115 	.if \enable
116 661:	\insn1
117 662:	.pushsection .altinstructions, "a"
118 	altinstruction_entry 661b, 663f, \cap, 662b-661b, 664f-663f
119 	.popsection
120 	.subsection 1
121 663:	\insn2
122 664:	.previous
123 	.org	. - (664b-663b) + (662b-661b)
124 	.org	. - (662b-661b) + (664b-663b)
125 	.endif
126 .endm
127 
128 /*
129  * Alternative sequences
130  *
131  * The code for the case where the capability is not present will be
132  * assembled and linked as normal. There are no restrictions on this
133  * code.
134  *
135  * The code for the case where the capability is present will be
136  * assembled into a special section to be used for dynamic patching.
137  * Code for that case must:
138  *
139  * 1. Be exactly the same length (in bytes) as the default code
140  *    sequence.
141  *
142  * 2. Not contain a branch target that is used outside of the
143  *    alternative sequence it is defined in (branches into an
144  *    alternative sequence are not fixed up).
145  */
146 
147 /*
148  * Begin an alternative code sequence.
149  */
150 .macro alternative_if_not cap
151 	.set .Lasm_alt_mode, 0
152 	.pushsection .altinstructions, "a"
153 	altinstruction_entry 661f, 663f, \cap, 662f-661f, 664f-663f
154 	.popsection
155 661:
156 .endm
157 
158 .macro alternative_if cap
159 	.set .Lasm_alt_mode, 1
160 	.pushsection .altinstructions, "a"
161 	altinstruction_entry 663f, 661f, \cap, 664f-663f, 662f-661f
162 	.popsection
163 	.subsection 1
164 	.align 2	/* So GAS knows label 661 is suitably aligned */
165 661:
166 .endm
167 
168 .macro alternative_cb cb
169 	.set .Lasm_alt_mode, 0
170 	.pushsection .altinstructions, "a"
171 	altinstruction_entry 661f, \cb, ARM64_CB_PATCH, 662f-661f, 0
172 	.popsection
173 661:
174 .endm
175 
176 /*
177  * Provide the other half of the alternative code sequence.
178  */
179 .macro alternative_else
180 662:
181 	.if .Lasm_alt_mode==0
182 	.subsection 1
183 	.else
184 	.previous
185 	.endif
186 663:
187 .endm
188 
189 /*
190  * Complete an alternative code sequence.
191  */
192 .macro alternative_endif
193 664:
194 	.if .Lasm_alt_mode==0
195 	.previous
196 	.endif
197 	.org	. - (664b-663b) + (662b-661b)
198 	.org	. - (662b-661b) + (664b-663b)
199 .endm
200 
201 /*
202  * Callback-based alternative epilogue
203  */
204 .macro alternative_cb_end
205 662:
206 .endm
207 
208 /*
209  * Provides a trivial alternative or default sequence consisting solely
210  * of NOPs. The number of NOPs is chosen automatically to match the
211  * previous case.
212  */
213 .macro alternative_else_nop_endif
214 alternative_else
215 	nops	(662b-661b) / AARCH64_INSN_SIZE
216 alternative_endif
217 .endm
218 
219 #define _ALTERNATIVE_CFG(insn1, insn2, cap, cfg, ...)	\
220 	alternative_insn insn1, insn2, cap, IS_ENABLED(cfg)
221 
222 .macro user_alt, label, oldinstr, newinstr, cond
223 9999:	alternative_insn "\oldinstr", "\newinstr", \cond
224 	_asm_extable 9999b, \label
225 .endm
226 
227 /*
228  * Generate the assembly for UAO alternatives with exception table entries.
229  * This is complicated as there is no post-increment or pair versions of the
230  * unprivileged instructions, and USER() only works for single instructions.
231  */
232 #ifdef CONFIG_ARM64_UAO
233 	.macro uao_ldp l, reg1, reg2, addr, post_inc
234 		alternative_if_not ARM64_HAS_UAO
235 8888:			ldp	\reg1, \reg2, [\addr], \post_inc;
236 8889:			nop;
237 			nop;
238 		alternative_else
239 			ldtr	\reg1, [\addr];
240 			ldtr	\reg2, [\addr, #8];
241 			add	\addr, \addr, \post_inc;
242 		alternative_endif
243 
244 		_asm_extable	8888b,\l;
245 		_asm_extable	8889b,\l;
246 	.endm
247 
248 	.macro uao_stp l, reg1, reg2, addr, post_inc
249 		alternative_if_not ARM64_HAS_UAO
250 8888:			stp	\reg1, \reg2, [\addr], \post_inc;
251 8889:			nop;
252 			nop;
253 		alternative_else
254 			sttr	\reg1, [\addr];
255 			sttr	\reg2, [\addr, #8];
256 			add	\addr, \addr, \post_inc;
257 		alternative_endif
258 
259 		_asm_extable	8888b,\l;
260 		_asm_extable	8889b,\l;
261 	.endm
262 
263 	.macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
264 		alternative_if_not ARM64_HAS_UAO
265 8888:			\inst	\reg, [\addr], \post_inc;
266 			nop;
267 		alternative_else
268 			\alt_inst	\reg, [\addr];
269 			add		\addr, \addr, \post_inc;
270 		alternative_endif
271 
272 		_asm_extable	8888b,\l;
273 	.endm
274 #else
275 	.macro uao_ldp l, reg1, reg2, addr, post_inc
276 		USER(\l, ldp \reg1, \reg2, [\addr], \post_inc)
277 	.endm
278 	.macro uao_stp l, reg1, reg2, addr, post_inc
279 		USER(\l, stp \reg1, \reg2, [\addr], \post_inc)
280 	.endm
281 	.macro uao_user_alternative l, inst, alt_inst, reg, addr, post_inc
282 		USER(\l, \inst \reg, [\addr], \post_inc)
283 	.endm
284 #endif
285 
286 #endif  /*  __ASSEMBLY__  */
287 
288 /*
289  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature));
290  *
291  * Usage: asm(ALTERNATIVE(oldinstr, newinstr, feature, CONFIG_FOO));
292  * N.B. If CONFIG_FOO is specified, but not selected, the whole block
293  *      will be omitted, including oldinstr.
294  */
295 #define ALTERNATIVE(oldinstr, newinstr, ...)   \
296 	_ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
297 
298 #endif /* __ASM_ALTERNATIVE_H */
299