alternative.c

 1// SPDX-License-Identifier: GPL-2.0
 2
 3#ifndef pr_fmt
 4#define pr_fmt(fmt)	"alt: " fmt
 5#endif
 6
 7#include <linux/uaccess.h>
 8#include <linux/printk.h>
 9#include <asm/nospec-branch.h>
10#include <asm/abs_lowcore.h>
11#include <asm/alternative.h>
12#include <asm/facility.h>
13#include <asm/sections.h>
14#include <asm/machine.h>
15
16#ifndef a_debug
17#define a_debug		pr_debug
18#endif
19
20#ifndef __kernel_va
21#define __kernel_va(x)	(void *)(x)
22#endif
23
24unsigned long __bootdata_preserved(machine_features[1]);
25
26struct alt_debug {
27	unsigned long facilities[MAX_FACILITY_BIT / BITS_PER_LONG];
28	unsigned long mfeatures[MAX_MFEATURE_BIT / BITS_PER_LONG];
29	int spec;
30};
31
32static struct alt_debug __bootdata_preserved(alt_debug);
33
34static void alternative_dump(u8 *old, u8 *new, unsigned int len, unsigned int type, unsigned int data)
35{
36	char oinsn[33], ninsn[33];
37	unsigned long kptr;
38	unsigned int pos;
39
40	for (pos = 0; pos < len && 2 * pos < sizeof(oinsn) - 3; pos++)
41		hex_byte_pack(&oinsn[2 * pos], old[pos]);
42	oinsn[2 * pos] = 0;
43	for (pos = 0; pos < len && 2 * pos < sizeof(ninsn) - 3; pos++)
44		hex_byte_pack(&ninsn[2 * pos], new[pos]);
45	ninsn[2 * pos] = 0;
46	kptr = (unsigned long)__kernel_va(old);
47	a_debug("[%d/%3d] %016lx: %s -> %s\n", type, data, kptr, oinsn, ninsn);
48}
49
50void __apply_alternatives(struct alt_instr *start, struct alt_instr *end, unsigned int ctx)
51{
52	struct alt_debug *d;
53	struct alt_instr *a;
54	bool debug, replace;
55	u8 *old, *new;
56
57	/*
58	 * The scan order should be from start to end. A later scanned
59	 * alternative code can overwrite previously scanned alternative code.
60	 */
61	d = &alt_debug;
62	for (a = start; a < end; a++) {
63		if (!(a->ctx & ctx))
64			continue;
65		switch (a->type) {
66		case ALT_TYPE_FACILITY:
67			replace = test_facility(a->data);
68			debug = __test_facility(a->data, d->facilities);
69			break;
70		case ALT_TYPE_FEATURE:
71			replace = test_machine_feature(a->data);
72			debug = __test_machine_feature(a->data, d->mfeatures);
73			break;
74		case ALT_TYPE_SPEC:
75			replace = nobp_enabled();
76			debug = d->spec;
77			break;
78		default:
79			replace = false;
80			debug = false;
81		}
82		if (!replace)
83			continue;
84		old = (u8 *)&a->instr_offset + a->instr_offset;
85		new = (u8 *)&a->repl_offset + a->repl_offset;
86		if (debug)
87			alternative_dump(old, new, a->instrlen, a->type, a->data);
88		s390_kernel_write(old, new, a->instrlen);
89	}
90}