1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/module.h>
3 #include <asm/alternative.h>
4 #include <asm/facility.h>
5 #include <asm/nospec-branch.h>
6
7 #define MAX_PATCH_LEN (255 - 1)
8
9 static int __initdata_or_module alt_instr_disabled;
10
disable_alternative_instructions(char * str)11 static int __init disable_alternative_instructions(char *str)
12 {
13 alt_instr_disabled = 1;
14 return 0;
15 }
16
17 early_param("noaltinstr", disable_alternative_instructions);
18
19 struct brcl_insn {
20 u16 opc;
21 s32 disp;
22 } __packed;
23
24 static u16 __initdata_or_module nop16 = 0x0700;
25 static u32 __initdata_or_module nop32 = 0x47000000;
26 static struct brcl_insn __initdata_or_module nop48 = {
27 0xc004, 0
28 };
29
30 static const void *nops[] __initdata_or_module = {
31 &nop16,
32 &nop32,
33 &nop48
34 };
35
add_jump_padding(void * insns,unsigned int len)36 static void __init_or_module add_jump_padding(void *insns, unsigned int len)
37 {
38 struct brcl_insn brcl = {
39 0xc0f4,
40 len / 2
41 };
42
43 memcpy(insns, &brcl, sizeof(brcl));
44 insns += sizeof(brcl);
45 len -= sizeof(brcl);
46
47 while (len > 0) {
48 memcpy(insns, &nop16, 2);
49 insns += 2;
50 len -= 2;
51 }
52 }
53
add_padding(void * insns,unsigned int len)54 static void __init_or_module add_padding(void *insns, unsigned int len)
55 {
56 if (len > 6)
57 add_jump_padding(insns, len);
58 else if (len >= 2)
59 memcpy(insns, nops[len / 2 - 1], len);
60 }
61
__apply_alternatives(struct alt_instr * start,struct alt_instr * end)62 static void __init_or_module __apply_alternatives(struct alt_instr *start,
63 struct alt_instr *end)
64 {
65 struct alt_instr *a;
66 u8 *instr, *replacement;
67 u8 insnbuf[MAX_PATCH_LEN];
68
69 /*
70 * The scan order should be from start to end. A later scanned
71 * alternative code can overwrite previously scanned alternative code.
72 */
73 for (a = start; a < end; a++) {
74 int insnbuf_sz = 0;
75
76 instr = (u8 *)&a->instr_offset + a->instr_offset;
77 replacement = (u8 *)&a->repl_offset + a->repl_offset;
78
79 if (!__test_facility(a->facility,
80 S390_lowcore.alt_stfle_fac_list))
81 continue;
82
83 if (unlikely(a->instrlen % 2 || a->replacementlen % 2)) {
84 WARN_ONCE(1, "cpu alternatives instructions length is "
85 "odd, skipping patching\n");
86 continue;
87 }
88
89 memcpy(insnbuf, replacement, a->replacementlen);
90 insnbuf_sz = a->replacementlen;
91
92 if (a->instrlen > a->replacementlen) {
93 add_padding(insnbuf + a->replacementlen,
94 a->instrlen - a->replacementlen);
95 insnbuf_sz += a->instrlen - a->replacementlen;
96 }
97
98 s390_kernel_write(instr, insnbuf, insnbuf_sz);
99 }
100 }
101
apply_alternatives(struct alt_instr * start,struct alt_instr * end)102 void __init_or_module apply_alternatives(struct alt_instr *start,
103 struct alt_instr *end)
104 {
105 if (!alt_instr_disabled)
106 __apply_alternatives(start, end);
107 }
108
109 extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
apply_alternative_instructions(void)110 void __init apply_alternative_instructions(void)
111 {
112 apply_alternatives(__alt_instructions, __alt_instructions_end);
113 }
114
