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 void __ref __static_call_transform(void *insn, enum insn_type type, void *func) 21 { 22 const void *emulate = NULL; 23 int size = CALL_INSN_SIZE; 24 const void *code; 25 26 switch (type) { 27 case CALL: 28 code = text_gen_insn(CALL_INSN_OPCODE, insn, func); 29 if (func == &__static_call_return0) { 30 emulate = code; 31 code = &xor5rax; 32 } 33 34 break; 35 36 case NOP: 37 code = x86_nops[5]; 38 break; 39 40 case JMP: 41 code = text_gen_insn(JMP32_INSN_OPCODE, insn, func); 42 break; 43 44 case RET: 45 code = text_gen_insn(RET_INSN_OPCODE, insn, func); 46 size = RET_INSN_SIZE; 47 break; 48 } 49 50 if (memcmp(insn, code, size) == 0) 51 return; 52 53 if (unlikely(system_state == SYSTEM_BOOTING)) 54 return text_poke_early(insn, code, size); 55 56 text_poke_bp(insn, code, size, emulate); 57 } 58 59 static void __static_call_validate(void *insn, bool tail) 60 { 61 u8 opcode = *(u8 *)insn; 62 63 if (tail) { 64 if (opcode == JMP32_INSN_OPCODE || 65 opcode == RET_INSN_OPCODE) 66 return; 67 } else { 68 if (opcode == CALL_INSN_OPCODE || 69 !memcmp(insn, x86_nops[5], 5) || 70 !memcmp(insn, xor5rax, 5)) 71 return; 72 } 73 74 /* 75 * If we ever trigger this, our text is corrupt, we'll probably not live long. 76 */ 77 WARN_ONCE(1, "unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn); 78 } 79 80 static inline enum insn_type __sc_insn(bool null, bool tail) 81 { 82 /* 83 * Encode the following table without branches: 84 * 85 * tail null insn 86 * -----+-------+------ 87 * 0 | 0 | CALL 88 * 0 | 1 | NOP 89 * 1 | 0 | JMP 90 * 1 | 1 | RET 91 */ 92 return 2*tail + null; 93 } 94 95 void arch_static_call_transform(void *site, void *tramp, void *func, bool tail) 96 { 97 mutex_lock(&text_mutex); 98 99 if (tramp) { 100 __static_call_validate(tramp, true); 101 __static_call_transform(tramp, __sc_insn(!func, true), func); 102 } 103 104 if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) { 105 __static_call_validate(site, tail); 106 __static_call_transform(site, __sc_insn(!func, tail), func); 107 } 108 109 mutex_unlock(&text_mutex); 110 } 111 EXPORT_SYMBOL_GPL(arch_static_call_transform); 112