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 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(bool disable); 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(bool disable) { 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 */ 117