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_ibt_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 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 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	val &= ~0x01000000U; /* ENDBR32 -> ENDBR64 */
 74	return val == gen_endbr();
 75}
 76
 77extern __noendbr u64 ibt_save(void);
 78extern __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
101static inline bool is_endbr(u32 val) { return false; }
102
103static inline u64 ibt_save(void) { return 0; }
104static 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 */