1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | #ifndef _ASM_X86_IBT_H |
3 | #define _ASM_X86_IBT_H |
4 | |
5 | #include <linux/types.h> |
6 | |
7 | /* |
8 | * The rules for enabling IBT are: |
9 | * |
10 | * - CC_HAS_IBT: the toolchain supports it |
11 | * - X86_KERNEL_IBT: it is selected in Kconfig |
12 | * - !__DISABLE_EXPORTS: this is regular kernel code |
13 | * |
14 | * Esp. that latter one is a bit non-obvious, but some code like compressed, |
15 | * purgatory, realmode etc.. is built with custom CFLAGS that do not include |
16 | * -fcf-protection=branch and things will go *bang*. |
17 | * |
18 | * When all the above are satisfied, HAS_KERNEL_IBT will be 1, otherwise 0. |
19 | */ |
20 | #if defined(CONFIG_X86_KERNEL_IBT) && !defined(__DISABLE_EXPORTS) |
21 | |
22 | #define HAS_KERNEL_IBT 1 |
23 | |
24 | #ifndef __ASSEMBLY__ |
25 | |
26 | #ifdef CONFIG_X86_64 |
27 | #define ASM_ENDBR "endbr64\n\t" |
28 | #else |
29 | #define ASM_ENDBR "endbr32\n\t" |
30 | #endif |
31 | |
32 | #define __noendbr __attribute__((nocf_check)) |
33 | |
34 | /* |
35 | * Create a dummy function pointer reference to prevent objtool from marking |
36 | * the function as needing to be "sealed" (i.e. ENDBR converted to NOP by |
37 | * apply_seal_endbr()). |
38 | */ |
39 | #define IBT_NOSEAL(fname) \ |
40 | ".pushsection .discard.ibt_endbr_noseal\n\t" \ |
41 | _ASM_PTR fname "\n\t" \ |
42 | ".popsection\n\t" |
43 | |
44 | static inline __attribute_const__ u32 gen_endbr(void) |
45 | { |
46 | u32 endbr; |
47 | |
48 | /* |
49 | * Generate ENDBR64 in a way that is sure to not result in |
50 | * an ENDBR64 instruction as immediate. |
51 | */ |
52 | asm ( "mov $~0xfa1e0ff3, %[endbr]\n\t" |
53 | "not %[endbr]\n\t" |
54 | : [endbr] "=&r" (endbr) ); |
55 | |
56 | return endbr; |
57 | } |
58 | |
59 | static inline __attribute_const__ u32 gen_endbr_poison(void) |
60 | { |
61 | /* |
62 | * 4 byte NOP that isn't NOP4 (in fact it is OSP NOP3), such that it |
63 | * will be unique to (former) ENDBR sites. |
64 | */ |
65 | return 0x001f0f66; /* osp nopl (%rax) */ |
66 | } |
67 | |
68 | static inline bool is_endbr(u32 val) |
69 | { |
70 | if (val == gen_endbr_poison()) |
71 | return true; |
72 | |
73 | val &= ~0x01000000U; /* ENDBR32 -> ENDBR64 */ |
74 | return val == gen_endbr(); |
75 | } |
76 | |
77 | extern __noendbr u64 ibt_save(bool disable); |
78 | extern __noendbr void ibt_restore(u64 save); |
79 | |
80 | #else /* __ASSEMBLY__ */ |
81 | |
82 | #ifdef CONFIG_X86_64 |
83 | #define ENDBR endbr64 |
84 | #else |
85 | #define ENDBR endbr32 |
86 | #endif |
87 | |
88 | #endif /* __ASSEMBLY__ */ |
89 | |
90 | #else /* !IBT */ |
91 | |
92 | #define HAS_KERNEL_IBT 0 |
93 | |
94 | #ifndef __ASSEMBLY__ |
95 | |
96 | #define ASM_ENDBR |
97 | #define IBT_NOSEAL(name) |
98 | |
99 | #define __noendbr |
100 | |
101 | static inline bool is_endbr(u32 val) { return false; } |
102 | |
103 | static inline u64 ibt_save(bool disable) { return 0; } |
104 | static inline void ibt_restore(u64 save) { } |
105 | |
106 | #else /* __ASSEMBLY__ */ |
107 | |
108 | #define ENDBR |
109 | |
110 | #endif /* __ASSEMBLY__ */ |
111 | |
112 | #endif /* CONFIG_X86_KERNEL_IBT */ |
113 | |
114 | #define ENDBR_INSN_SIZE (4*HAS_KERNEL_IBT) |
115 | |
116 | #endif /* _ASM_X86_IBT_H */ |
117 | |