LXR linux/arch/s390/kernel/alternative.c

   1// SPDX-License-Identifier: GPL-2.0
   2#include <linux/module.h>
   3#include <asm/alternative.h>
   4#include <asm/facility.h>
   5
   6#define MAX_PATCH_LEN (255 - 1)
   7
   8static int __initdata_or_module alt_instr_disabled;
   9
  10static int __init disable_alternative_instructions(char *str)
  11{
  12        alt_instr_disabled = 1;
  13        return 0;
  14}
  15
  16early_param("noaltinstr", disable_alternative_instructions);
  17
  18static int __init nobp_setup_early(char *str)
  19{
  20        bool enabled;
  21        int rc;
  22
  23        rc = kstrtobool(str, &enabled);
  24        if (rc)
  25                return rc;
  26        if (enabled && test_facility(82))
  27                __set_facility(82, S390_lowcore.alt_stfle_fac_list);
  28        else
  29                __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
  30        return 0;
  31}
  32early_param("nobp", nobp_setup_early);
  33
  34static int __init nospec_setup_early(char *str)
  35{
  36        __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
  37        return 0;
  38}
  39early_param("nospec", nospec_setup_early);
  40
  41struct brcl_insn {
  42        u16 opc;
  43        s32 disp;
  44} __packed;
  45
  46static u16 __initdata_or_module nop16 = 0x0700;
  47static u32 __initdata_or_module nop32 = 0x47000000;
  48static struct brcl_insn __initdata_or_module nop48 = {
  49        0xc004, 0
  50};
  51
  52static const void *nops[] __initdata_or_module = {
  53        &nop16,
  54        &nop32,
  55        &nop48
  56};
  57
  58static void __init_or_module add_jump_padding(void *insns, unsigned int len)
  59{
  60        struct brcl_insn brcl = {
  61                0xc0f4,
  62                len / 2
  63        };
  64
  65        memcpy(insns, &brcl, sizeof(brcl));
  66        insns += sizeof(brcl);
  67        len -= sizeof(brcl);
  68
  69        while (len > 0) {
  70                memcpy(insns, &nop16, 2);
  71                insns += 2;
  72                len -= 2;
  73        }
  74}
  75
  76static void __init_or_module add_padding(void *insns, unsigned int len)
  77{
  78        if (len > 6)
  79                add_jump_padding(insns, len);
  80        else if (len >= 2)
  81                memcpy(insns, nops[len / 2 - 1], len);
  82}
  83
  84static void __init_or_module __apply_alternatives(struct alt_instr *start,
  85                                                  struct alt_instr *end)
  86{
  87        struct alt_instr *a;
  88        u8 *instr, *replacement;
  89        u8 insnbuf[MAX_PATCH_LEN];
  90
  91        /*
  92         * The scan order should be from start to end. A later scanned
  93         * alternative code can overwrite previously scanned alternative code.
  94         */
  95        for (a = start; a < end; a++) {
  96                int insnbuf_sz = 0;
  97
  98                instr = (u8 *)&a->instr_offset + a->instr_offset;
  99                replacement = (u8 *)&a->repl_offset + a->repl_offset;
 100
 101                if (!__test_facility(a->facility,
 102                                     S390_lowcore.alt_stfle_fac_list))
 103                        continue;
 104
 105                if (unlikely(a->instrlen % 2 || a->replacementlen % 2)) {
 106                        WARN_ONCE(1, "cpu alternatives instructions length is "
 107                                     "odd, skipping patching\n");
 108                        continue;
 109                }
 110
 111                memcpy(insnbuf, replacement, a->replacementlen);
 112                insnbuf_sz = a->replacementlen;
 113
 114                if (a->instrlen > a->replacementlen) {
 115                        add_padding(insnbuf + a->replacementlen,
 116                                    a->instrlen - a->replacementlen);
 117                        insnbuf_sz += a->instrlen - a->replacementlen;
 118                }
 119
 120                s390_kernel_write(instr, insnbuf, insnbuf_sz);
 121        }
 122}
 123
 124void __init_or_module apply_alternatives(struct alt_instr *start,
 125                                         struct alt_instr *end)
 126{
 127        if (!alt_instr_disabled)
 128                __apply_alternatives(start, end);
 129}
 130
 131extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
 132void __init apply_alternative_instructions(void)
 133{
 134        apply_alternatives(__alt_instructions, __alt_instructions_end);
 135}
 136