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 __ASSEMBLER__
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
44static __always_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
59static __always_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
68static inline bool __is_endbr(u32 val)
69{
70 if (val == gen_endbr_poison())
71 return true;
72
73 /* See cfi_fineibt_bhi_preamble() */
74 if (IS_ENABLED(CONFIG_FINEIBT_BHI) && val == 0x001f0ff5)
75 return true;
76
77 val &= ~0x01000000U; /* ENDBR32 -> ENDBR64 */
78 return val == gen_endbr();
79}
80
81extern __noendbr bool is_endbr(u32 *val);
82extern __noendbr u64 ibt_save(bool disable);
83extern __noendbr void ibt_restore(u64 save);
84
85#else /* __ASSEMBLER__ */
86
87#ifdef CONFIG_X86_64
88#define ENDBR endbr64
89#else
90#define ENDBR endbr32
91#endif
92
93#endif /* __ASSEMBLER__ */
94
95#else /* !IBT */
96
97#define HAS_KERNEL_IBT 0
98
99#ifndef __ASSEMBLER__
100
101#define ASM_ENDBR
102#define IBT_NOSEAL(name)
103
104#define __noendbr
105
106static inline bool is_endbr(u32 *val) { return false; }
107
108static inline u64 ibt_save(bool disable) { return 0; }
109static inline void ibt_restore(u64 save) { }
110
111#else /* __ASSEMBLER__ */
112
113#define ENDBR
114
115#endif /* __ASSEMBLER__ */
116
117#endif /* CONFIG_X86_KERNEL_IBT */
118
119#define ENDBR_INSN_SIZE (4*HAS_KERNEL_IBT)
120
121#endif /* _ASM_X86_IBT_H */
122

source code of linux/arch/x86/include/asm/ibt.h