Release 4.15 arch/s390/kernel/alternative.c
// SPDX-License-Identifier: GPL-2.0
#include <linux/module.h>
#include <asm/alternative.h>
#include <asm/facility.h>
#define MAX_PATCH_LEN (255 - 1)
static int __initdata_or_module alt_instr_disabled;
static int __init disable_alternative_instructions(char *str)
{
alt_instr_disabled = 1;
return 0;
}
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early_param("noaltinstr", disable_alternative_instructions);
struct brcl_insn {
u16 opc;
s32 disp;
} __packed;
static u16 __initdata_or_module nop16 = 0x0700;
static u32 __initdata_or_module nop32 = 0x47000000;
static struct brcl_insn __initdata_or_module nop48 = {
0xc004, 0
};
static const void *nops[] __initdata_or_module = {
&nop16,
&nop32,
&nop48
};
static void __init_or_module add_jump_padding(void *insns, unsigned int len)
{
struct brcl_insn brcl = {
0xc0f4,
len / 2
};
memcpy(insns, &brcl, sizeof(brcl));
insns += sizeof(brcl);
len -= sizeof(brcl);
while (len > 0) {
memcpy(insns, &nop16, 2);
insns += 2;
len -= 2;
}
}
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static void __init_or_module add_padding(void *insns, unsigned int len)
{
if (len > 6)
add_jump_padding(insns, len);
else if (len >= 2)
memcpy(insns, nops[len / 2 - 1], len);
}
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static void __init_or_module __apply_alternatives(struct alt_instr *start,
struct alt_instr *end)
{
struct alt_instr *a;
u8 *instr, *replacement;
u8 insnbuf[MAX_PATCH_LEN];
/*
* The scan order should be from start to end. A later scanned
* alternative code can overwrite previously scanned alternative code.
*/
for (a = start; a < end; a++) {
int insnbuf_sz = 0;
instr = (u8 *)&a->instr_offset + a->instr_offset;
replacement = (u8 *)&a->repl_offset + a->repl_offset;
if (!test_facility(a->facility))
continue;
if (unlikely(a->instrlen % 2 || a->replacementlen % 2)) {
WARN_ONCE(1, "cpu alternatives instructions length is "
"odd, skipping patching\n");
continue;
}
memcpy(insnbuf, replacement, a->replacementlen);
insnbuf_sz = a->replacementlen;
if (a->instrlen > a->replacementlen) {
add_padding(insnbuf + a->replacementlen,
a->instrlen - a->replacementlen);
insnbuf_sz += a->instrlen - a->replacementlen;
}
s390_kernel_write(instr, insnbuf, insnbuf_sz);
}
}
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void __init_or_module apply_alternatives(struct alt_instr *start,
struct alt_instr *end)
{
if (!alt_instr_disabled)
__apply_alternatives(start, end);
}
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extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
void __init apply_alternative_instructions(void)
{
apply_alternatives(__alt_instructions, __alt_instructions_end);
}
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