1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/module.h>
3 #include <linux/device.h>
5 #include <asm/facility.h>
6 #include <asm/nospec-branch.h>
8 static int __init
nobp_setup_early(char *str
)
13 rc
= kstrtobool(str
, &enabled
);
16 if (enabled
&& test_facility(82)) {
18 * The user explicitely requested nobp=1, enable it and
19 * disable the expoline support.
21 __set_facility(82, S390_lowcore
.alt_stfle_fac_list
);
22 if (IS_ENABLED(CONFIG_EXPOLINE
))
25 __clear_facility(82, S390_lowcore
.alt_stfle_fac_list
);
29 early_param("nobp", nobp_setup_early
);
31 static int __init
nospec_setup_early(char *str
)
33 __clear_facility(82, S390_lowcore
.alt_stfle_fac_list
);
36 early_param("nospec", nospec_setup_early
);
38 static int __init
nospec_report(void)
40 if (IS_ENABLED(CC_USING_EXPOLINE
) && !nospec_disable
)
41 pr_info("Spectre V2 mitigation: execute trampolines.\n");
42 if (__test_facility(82, S390_lowcore
.alt_stfle_fac_list
))
43 pr_info("Spectre V2 mitigation: limited branch prediction.\n");
46 arch_initcall(nospec_report
);
48 #ifdef CONFIG_EXPOLINE
50 int nospec_disable
= IS_ENABLED(CONFIG_EXPOLINE_OFF
);
52 static int __init
nospectre_v2_setup_early(char *str
)
57 early_param("nospectre_v2", nospectre_v2_setup_early
);
60 void __init
nospec_auto_detect(void)
62 if (cpu_mitigations_off()) {
64 * Disable expolines and disable nobp.
66 if (IS_ENABLED(CC_USING_EXPOLINE
))
68 __clear_facility(82, S390_lowcore
.alt_stfle_fac_list
);
69 if (IS_ENABLED(CC_USING_EXPOLINE
)) {
71 * The kernel has been compiled with expolines.
72 * Keep expolines enabled and disable nobp.
75 __clear_facility(82, S390_lowcore
.alt_stfle_fac_list
);
78 * If the kernel has not been compiled with expolines the
79 * nobp setting decides what is done, this depends on the
80 * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
84 static int __init
spectre_v2_setup_early(char *str
)
86 if (str
&& !strncmp(str
, "on", 2)) {
88 __clear_facility(82, S390_lowcore
.alt_stfle_fac_list
);
90 if (str
&& !strncmp(str
, "off", 3))
92 if (str
&& !strncmp(str
, "auto", 4))
96 early_param("spectre_v2", spectre_v2_setup_early
);
98 static void __init_or_module
__nospec_revert(s32
*start
, s32
*end
)
100 enum { BRCL_EXPOLINE
, BRASL_EXPOLINE
} type
;
101 u8
*instr
, *thunk
, *br
;
105 /* Second part of the instruction replace is always a nop */
106 for (epo
= start
; epo
< end
; epo
++) {
107 instr
= (u8
*) epo
+ *epo
;
108 if (instr
[0] == 0xc0 && (instr
[1] & 0x0f) == 0x04)
109 type
= BRCL_EXPOLINE
; /* brcl instruction */
110 else if (instr
[0] == 0xc0 && (instr
[1] & 0x0f) == 0x05)
111 type
= BRASL_EXPOLINE
; /* brasl instruction */
114 thunk
= instr
+ (*(int *)(instr
+ 2)) * 2;
115 if (thunk
[0] == 0xc6 && thunk
[1] == 0x00)
116 /* exrl %r0,<target-br> */
117 br
= thunk
+ (*(int *)(thunk
+ 2)) * 2;
118 else if (thunk
[0] == 0xc0 && (thunk
[1] & 0x0f) == 0x00 &&
119 thunk
[6] == 0x44 && thunk
[7] == 0x00 &&
120 (thunk
[8] & 0x0f) == 0x00 && thunk
[9] == 0x00 &&
121 (thunk
[1] & 0xf0) == (thunk
[8] & 0xf0))
122 /* larl %rx,<target br> + ex %r0,0(%rx) */
123 br
= thunk
+ (*(int *)(thunk
+ 2)) * 2;
126 /* Check for unconditional branch 0x07f? or 0x47f???? */
127 if ((br
[0] & 0xbf) != 0x07 || (br
[1] & 0xf0) != 0xf0)
130 memcpy(insnbuf
+ 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
134 insnbuf
[1] = (instr
[1] & 0xf0) | (br
[1] & 0x0f);
136 /* brcl to b, replace with bc + nopr */
140 /* brcl to br, replace with bcr + nop */
144 insnbuf
[1] = (instr
[1] & 0xf0) | (br
[1] & 0x0f);
146 /* brasl to b, replace with bas + nopr */
151 /* brasl to br, replace with basr + nop */
157 s390_kernel_write(instr
, insnbuf
, 6);
161 void __init_or_module
nospec_revert(s32
*start
, s32
*end
)
164 __nospec_revert(start
, end
);
167 extern s32 __nospec_call_start
[], __nospec_call_end
[];
168 extern s32 __nospec_return_start
[], __nospec_return_end
[];
169 void __init
nospec_init_branches(void)
171 nospec_revert(__nospec_call_start
, __nospec_call_end
);
172 nospec_revert(__nospec_return_start
, __nospec_return_end
);
175 #endif /* CONFIG_EXPOLINE */