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1 | /* SPDX-License-Identifier: GPL-2.0 */ | |
2 | ||
3 | #ifndef __NOSPEC_BRANCH_H__ | |
4 | #define __NOSPEC_BRANCH_H__ | |
5 | ||
6 | #include <asm/alternative.h> | |
7 | #include <asm/alternative-asm.h> | |
8 | #include <asm/cpufeatures.h> | |
9 | ||
10 | #ifdef __ASSEMBLY__ | |
11 | ||
12 | /* | |
13 | * This should be used immediately before a retpoline alternative. It tells | |
14 | * objtool where the retpolines are so that it can make sense of the control | |
15 | * flow by just reading the original instruction(s) and ignoring the | |
16 | * alternatives. | |
17 | */ | |
18 | .macro ANNOTATE_NOSPEC_ALTERNATIVE | |
19 | .Lannotate_\@: | |
20 | .pushsection .discard.nospec | |
21 | .long .Lannotate_\@ - . | |
22 | .popsection | |
23 | .endm | |
24 | ||
25 | /* | |
26 | * This should be used immediately before an indirect jump/call. It tells | |
27 | * objtool the subsequent indirect jump/call is vouched safe for retpoline | |
28 | * builds. | |
29 | */ | |
30 | .macro ANNOTATE_RETPOLINE_SAFE | |
31 | .Lannotate_\@: | |
32 | .pushsection .discard.retpoline_safe | |
33 | _ASM_PTR .Lannotate_\@ | |
34 | .popsection | |
35 | .endm | |
36 | ||
37 | /* | |
38 | * These are the bare retpoline primitives for indirect jmp and call. | |
39 | * Do not use these directly; they only exist to make the ALTERNATIVE | |
40 | * invocation below less ugly. | |
41 | */ | |
42 | .macro RETPOLINE_JMP reg:req | |
43 | call .Ldo_rop_\@ | |
44 | .Lspec_trap_\@: | |
45 | pause | |
46 | lfence | |
47 | jmp .Lspec_trap_\@ | |
48 | .Ldo_rop_\@: | |
49 | mov \reg, (%_ASM_SP) | |
50 | ret | |
51 | .endm | |
52 | ||
53 | /* | |
54 | * This is a wrapper around RETPOLINE_JMP so the called function in reg | |
55 | * returns to the instruction after the macro. | |
56 | */ | |
57 | .macro RETPOLINE_CALL reg:req | |
58 | jmp .Ldo_call_\@ | |
59 | .Ldo_retpoline_jmp_\@: | |
60 | RETPOLINE_JMP \reg | |
61 | .Ldo_call_\@: | |
62 | call .Ldo_retpoline_jmp_\@ | |
63 | .endm | |
64 | ||
65 | /* | |
66 | * JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple | |
67 | * indirect jmp/call which may be susceptible to the Spectre variant 2 | |
68 | * attack. | |
69 | */ | |
70 | .macro JMP_NOSPEC reg:req | |
71 | #ifdef CONFIG_RETPOLINE | |
72 | ANNOTATE_NOSPEC_ALTERNATIVE | |
73 | ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *\reg), \ | |
74 | __stringify(RETPOLINE_JMP \reg), X86_FEATURE_RETPOLINE, \ | |
75 | __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *\reg), X86_FEATURE_RETPOLINE_AMD | |
76 | #else | |
77 | jmp *\reg | |
78 | #endif | |
79 | .endm | |
80 | ||
81 | .macro CALL_NOSPEC reg:req | |
82 | #ifdef CONFIG_RETPOLINE | |
83 | ANNOTATE_NOSPEC_ALTERNATIVE | |
84 | ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *\reg), \ | |
85 | __stringify(RETPOLINE_CALL \reg), X86_FEATURE_RETPOLINE,\ | |
86 | __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *\reg), X86_FEATURE_RETPOLINE_AMD | |
87 | #else | |
88 | call *\reg | |
89 | #endif | |
90 | .endm | |
91 | ||
92 | /* This clobbers the BX register */ | |
93 | .macro FILL_RETURN_BUFFER nr:req ftr:req | |
94 | #ifdef CONFIG_RETPOLINE | |
95 | ALTERNATIVE "", "call __clear_rsb", \ftr | |
96 | #endif | |
97 | .endm | |
98 | ||
99 | #else /* __ASSEMBLY__ */ | |
100 | ||
101 | #define ANNOTATE_NOSPEC_ALTERNATIVE \ | |
102 | "999:\n\t" \ | |
103 | ".pushsection .discard.nospec\n\t" \ | |
104 | ".long 999b - .\n\t" \ | |
105 | ".popsection\n\t" | |
106 | ||
107 | #define ANNOTATE_RETPOLINE_SAFE \ | |
108 | "999:\n\t" \ | |
109 | ".pushsection .discard.retpoline_safe\n\t" \ | |
110 | _ASM_PTR " 999b\n\t" \ | |
111 | ".popsection\n\t" | |
112 | ||
113 | #if defined(CONFIG_X86_64) && defined(RETPOLINE) | |
114 | ||
115 | /* | |
116 | * Since the inline asm uses the %V modifier which is only in newer GCC, | |
117 | * the 64-bit one is dependent on RETPOLINE not CONFIG_RETPOLINE. | |
118 | */ | |
119 | # define CALL_NOSPEC \ | |
120 | ANNOTATE_NOSPEC_ALTERNATIVE \ | |
121 | ALTERNATIVE( \ | |
122 | ANNOTATE_RETPOLINE_SAFE \ | |
123 | "call *%[thunk_target]\n", \ | |
124 | "call __x86_indirect_thunk_%V[thunk_target]\n", \ | |
125 | X86_FEATURE_RETPOLINE) | |
126 | # define THUNK_TARGET(addr) [thunk_target] "r" (addr) | |
127 | ||
128 | #elif defined(CONFIG_X86_32) && defined(CONFIG_RETPOLINE) | |
129 | /* | |
130 | * For i386 we use the original ret-equivalent retpoline, because | |
131 | * otherwise we'll run out of registers. We don't care about CET | |
132 | * here, anyway. | |
133 | */ | |
134 | # define CALL_NOSPEC \ | |
135 | ALTERNATIVE( \ | |
136 | ANNOTATE_RETPOLINE_SAFE \ | |
137 | "call *%[thunk_target]\n", \ | |
138 | " jmp 904f;\n" \ | |
139 | " .align 16\n" \ | |
140 | "901: call 903f;\n" \ | |
141 | "902: pause;\n" \ | |
142 | " lfence;\n" \ | |
143 | " jmp 902b;\n" \ | |
144 | " .align 16\n" \ | |
145 | "903: addl $4, %%esp;\n" \ | |
146 | " pushl %[thunk_target];\n" \ | |
147 | " ret;\n" \ | |
148 | " .align 16\n" \ | |
149 | "904: call 901b;\n", \ | |
150 | X86_FEATURE_RETPOLINE) | |
151 | ||
152 | # define THUNK_TARGET(addr) [thunk_target] "rm" (addr) | |
153 | #else /* No retpoline for C / inline asm */ | |
154 | # define CALL_NOSPEC "call *%[thunk_target]\n" | |
155 | # define THUNK_TARGET(addr) [thunk_target] "rm" (addr) | |
156 | #endif | |
157 | ||
158 | /* The Spectre V2 mitigation variants */ | |
159 | enum spectre_v2_mitigation { | |
160 | SPECTRE_V2_NONE, | |
161 | SPECTRE_V2_RETPOLINE_MINIMAL, | |
162 | SPECTRE_V2_RETPOLINE_MINIMAL_AMD, | |
163 | SPECTRE_V2_RETPOLINE_GENERIC, | |
164 | SPECTRE_V2_RETPOLINE_AMD, | |
165 | SPECTRE_V2_IBRS, | |
166 | }; | |
167 | ||
168 | /* | |
169 | * On VMEXIT we must ensure that no RSB predictions learned in the guest | |
170 | * can be followed in the host, by overwriting the RSB completely. Both | |
171 | * retpoline and IBRS mitigations for Spectre v2 need this; only on future | |
172 | * CPUs with IBRS_ATT *might* it be avoided. | |
173 | */ | |
174 | static inline void vmexit_fill_RSB(void) | |
175 | { | |
176 | #ifdef CONFIG_RETPOLINE | |
177 | alternative_input("", | |
178 | "call __fill_rsb", | |
179 | X86_FEATURE_RETPOLINE, | |
180 | ASM_NO_INPUT_CLOBBER(_ASM_BX, "memory")); | |
181 | #endif | |
182 | } | |
183 | ||
184 | #endif /* __ASSEMBLY__ */ | |
185 | #endif /* __NOSPEC_BRANCH_H__ */ |