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 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 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 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 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 } 101 102 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[]; 110 void __init apply_alternative_instructions(void) 111 { 112 apply_alternatives(__alt_instructions, __alt_instructions_end); 113 } 114