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 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(void); 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(void) { 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