1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/static_call.h> 3 #include <linux/memory.h> 4 #include <linux/bug.h> 5 #include <asm/text-patching.h> 6 7 enum insn_type { 8 CALL = 0, /* site call */ 9 NOP = 1, /* site cond-call */ 10 JMP = 2, /* tramp / site tail-call */ 11 RET = 3, /* tramp / site cond-tail-call */ 12 }; 13 14 /* 15 * data16 data16 xorq %rax, %rax - a single 5 byte instruction that clears %rax 16 * The REX.W cancels the effect of any data16. 17 */ 18 static const u8 xor5rax[] = { 0x66, 0x66, 0x48, 0x31, 0xc0 }; 19 20 static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc }; 21 22 static void __ref __static_call_transform(void *insn, enum insn_type type, void *func) 23 { 24 const void *emulate = NULL; 25 int size = CALL_INSN_SIZE; 26 const void *code; 27 28 switch (type) { 29 case CALL: 30 code = text_gen_insn(CALL_INSN_OPCODE, insn, func); 31 if (func == &__static_call_return0) { 32 emulate = code; 33 code = &xor5rax; 34 } 35 36 break; 37 38 case NOP: 39 code = x86_nops[5]; 40 break; 41 42 case JMP: 43 code = text_gen_insn(JMP32_INSN_OPCODE, insn, func); 44 break; 45 46 case RET: 47 code = &retinsn; 48 break; 49 } 50 51 if (memcmp(insn, code, size) == 0) 52 return; 53 54 if (unlikely(system_state == SYSTEM_BOOTING)) 55 return text_poke_early(insn, code, size); 56 57 text_poke_bp(insn, code, size, emulate); 58 } 59 60 static void __static_call_validate(void *insn, bool tail, bool tramp) 61 { 62 u8 opcode = *(u8 *)insn; 63 64 if (tramp && memcmp(insn+5, "SCT", 3)) { 65 pr_err("trampoline signature fail"); 66 BUG(); 67 } 68 69 if (tail) { 70 if (opcode == JMP32_INSN_OPCODE || 71 opcode == RET_INSN_OPCODE) 72 return; 73 } else { 74 if (opcode == CALL_INSN_OPCODE || 75 !memcmp(insn, x86_nops[5], 5) || 76 !memcmp(insn, xor5rax, 5)) 77 return; 78 } 79 80 /* 81 * If we ever trigger this, our text is corrupt, we'll probably not live long. 82 */ 83 pr_err("unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn); 84 BUG(); 85 } 86 87 static inline enum insn_type __sc_insn(bool null, bool tail) 88 { 89 /* 90 * Encode the following table without branches: 91 * 92 * tail null insn 93 * -----+-------+------ 94 * 0 | 0 | CALL 95 * 0 | 1 | NOP 96 * 1 | 0 | JMP 97 * 1 | 1 | RET 98 */ 99 return 2*tail + null; 100 } 101 102 void arch_static_call_transform(void *site, void *tramp, void *func, bool tail) 103 { 104 mutex_lock(&text_mutex); 105 106 if (tramp) { 107 __static_call_validate(tramp, true, true); 108 __static_call_transform(tramp, __sc_insn(!func, true), func); 109 } 110 111 if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) { 112 __static_call_validate(site, tail, false); 113 __static_call_transform(site, __sc_insn(!func, tail), func); 114 } 115 116 mutex_unlock(&text_mutex); 117 } 118 EXPORT_SYMBOL_GPL(arch_static_call_transform); 119