1// SPDX-License-Identifier: GPL-2.0
2#include <linux/module.h>
3#include <linux/device.h>
4#include <linux/cpu.h>
5#include <asm/nospec-branch.h>
6
7static int __init nobp_setup_early(char *str)
8{
9	bool enabled;
10	int rc;
11
12	rc = kstrtobool(str, &enabled);
13	if (rc)
14		return rc;
15	if (enabled && test_facility(82)) {
16		/*
17		 * The user explicitly requested nobp=1, enable it and
18		 * disable the expoline support.
19		 */
20		__set_facility(82, alt_stfle_fac_list);
21		if (IS_ENABLED(CONFIG_EXPOLINE))
22			nospec_disable = 1;
23	} else {
24		__clear_facility(82, alt_stfle_fac_list);
25	}
26	return 0;
27}
28early_param("nobp", nobp_setup_early);
29
30static int __init nospec_setup_early(char *str)
31{
32	__clear_facility(82, alt_stfle_fac_list);
33	return 0;
34}
35early_param("nospec", nospec_setup_early);
36
37static int __init nospec_report(void)
38{
39	if (test_facility(156))
40		pr_info("Spectre V2 mitigation: etokens\n");
41	if (nospec_uses_trampoline())
42		pr_info("Spectre V2 mitigation: execute trampolines\n");
43	if (__test_facility(82, alt_stfle_fac_list))
44		pr_info("Spectre V2 mitigation: limited branch prediction\n");
45	return 0;
46}
47arch_initcall(nospec_report);
48
49#ifdef CONFIG_EXPOLINE
50
51int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
52
53static int __init nospectre_v2_setup_early(char *str)
54{
55	nospec_disable = 1;
56	return 0;
57}
58early_param("nospectre_v2", nospectre_v2_setup_early);
59
60void __init nospec_auto_detect(void)
61{
62	if (test_facility(156) || cpu_mitigations_off()) {
63		/*
64		 * The machine supports etokens.
65		 * Disable expolines and disable nobp.
66		 */
67		if (__is_defined(CC_USING_EXPOLINE))
68			nospec_disable = 1;
69		__clear_facility(82, alt_stfle_fac_list);
70	} else if (__is_defined(CC_USING_EXPOLINE)) {
71		/*
72		 * The kernel has been compiled with expolines.
73		 * Keep expolines enabled and disable nobp.
74		 */
75		nospec_disable = 0;
76		__clear_facility(82, alt_stfle_fac_list);
77	}
78	/*
79	 * If the kernel has not been compiled with expolines the
80	 * nobp setting decides what is done, this depends on the
81	 * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
82	 */
83}
84
85static int __init spectre_v2_setup_early(char *str)
86{
87	if (str && !strncmp(str, "on", 2)) {
88		nospec_disable = 0;
89		__clear_facility(82, alt_stfle_fac_list);
90	}
91	if (str && !strncmp(str, "off", 3))
92		nospec_disable = 1;
93	if (str && !strncmp(str, "auto", 4))
94		nospec_auto_detect();
95	return 0;
96}
97early_param("spectre_v2", spectre_v2_setup_early);
98
99static void __init_or_module __nospec_revert(s32 *start, s32 *end)
100{
101	enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
102	static const u8 branch[] = { 0x47, 0x00, 0x07, 0x00 };
103	u8 *instr, *thunk, *br;
104	u8 insnbuf[6];
105	s32 *epo;
106
107	/* Second part of the instruction replace is always a nop */
108	memcpy(insnbuf + 2, branch, sizeof(branch));
109	for (epo = start; epo < end; epo++) {
110		instr = (u8 *) epo + *epo;
111		if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
112			type = BRCL_EXPOLINE;	/* brcl instruction */
113		else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
114			type = BRASL_EXPOLINE;	/* brasl instruction */
115		else
116			continue;
117		thunk = instr + (*(int *)(instr + 2)) * 2;
118		if (thunk[0] == 0xc6 && thunk[1] == 0x00)
119			/* exrl %r0,<target-br> */
120			br = thunk + (*(int *)(thunk + 2)) * 2;
121		else
122			continue;
123		if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
124			continue;
125		switch (type) {
126		case BRCL_EXPOLINE:
127			/* brcl to thunk, replace with br + nop */
128			insnbuf[0] = br[0];
129			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
130			break;
131		case BRASL_EXPOLINE:
132			/* brasl to thunk, replace with basr + nop */
133			insnbuf[0] = 0x0d;
134			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
135			break;
136		}
137
138		s390_kernel_write(instr, insnbuf, 6);
139	}
140}
141
142void __init_or_module nospec_revert(s32 *start, s32 *end)
143{
144	if (nospec_disable)
145		__nospec_revert(start, end);
146}
147
148extern s32 __nospec_call_start[], __nospec_call_end[];
149extern s32 __nospec_return_start[], __nospec_return_end[];
150void __init nospec_init_branches(void)
151{
152	nospec_revert(__nospec_call_start, __nospec_call_end);
153	nospec_revert(__nospec_return_start, __nospec_return_end);
154}
155
156#endif /* CONFIG_EXPOLINE */
157