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, bool tramp) 60 { 61 u8 opcode = *(u8 *)insn; 62 63 if (tramp && memcmp(insn+5, "SCT", 3)) { 64 pr_err("trampoline signature fail"); 65 BUG(); 66 } 67 68 if (tail) { 69 if (opcode == JMP32_INSN_OPCODE || 70 opcode == RET_INSN_OPCODE) 71 return; 72 } else { 73 if (opcode == CALL_INSN_OPCODE || 74 !memcmp(insn, x86_nops[5], 5) || 75 !memcmp(insn, xor5rax, 5)) 76 return; 77 } 78 79 /* 80 * If we ever trigger this, our text is corrupt, we'll probably not live long. 81 */ 82 pr_err("unexpected static_call insn opcode 0x%x at %pS\n", opcode, insn); 83 BUG(); 84 } 85 86 static inline enum insn_type __sc_insn(bool null, bool tail) 87 { 88 /* 89 * Encode the following table without branches: 90 * 91 * tail null insn 92 * -----+-------+------ 93 * 0 | 0 | CALL 94 * 0 | 1 | NOP 95 * 1 | 0 | JMP 96 * 1 | 1 | RET 97 */ 98 return 2*tail + null; 99 } 100 101 void arch_static_call_transform(void *site, void *tramp, void *func, bool tail) 102 { 103 mutex_lock(&text_mutex); 104 105 if (tramp) { 106 __static_call_validate(tramp, true, true); 107 __static_call_transform(tramp, __sc_insn(!func, true), func); 108 } 109 110 if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) { 111 __static_call_validate(site, tail, false); 112 __static_call_transform(site, __sc_insn(!func, tail), func); 113 } 114 115 mutex_unlock(&text_mutex); 116 } 117 EXPORT_SYMBOL_GPL(arch_static_call_transform); 118