1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Clang Control Flow Integrity (CFI) support. 4 * 5 * Copyright (C) 2022 Google LLC 6 */ 7 #include <linux/string.h> 8 #include <linux/cfi.h> 9 #include <asm/insn.h> 10 #include <asm/insn-eval.h> 11 12 /* 13 * Returns the target address and the expected type when regs->ip points 14 * to a compiler-generated CFI trap. 15 */ 16 static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target, 17 u32 *type) 18 { 19 char buffer[MAX_INSN_SIZE]; 20 struct insn insn; 21 int offset = 0; 22 23 *target = *type = 0; 24 25 /* 26 * The compiler generates the following instruction sequence 27 * for indirect call checks: 28 * 29 * movl -<id>, %r10d ; 6 bytes 30 * addl -<pos>(%reg), %r10d; 4 bytes 31 * je .Ltmp1 ; 2 bytes 32 * ud2 ; <- regs->ip 33 * .Ltmp1: 34 * 35 * We can decode the expected type and the target address from the 36 * movl/addl instructions. 37 */ 38 if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 12, MAX_INSN_SIZE)) 39 return false; 40 if (insn_decode_kernel(&insn, &buffer[offset])) 41 return false; 42 if (insn.opcode.value != 0xBA) 43 return false; 44 45 *type = -(u32)insn.immediate.value; 46 47 if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 6, MAX_INSN_SIZE)) 48 return false; 49 if (insn_decode_kernel(&insn, &buffer[offset])) 50 return false; 51 if (insn.opcode.value != 0x3) 52 return false; 53 54 /* Read the target address from the register. */ 55 offset = insn_get_modrm_rm_off(&insn, regs); 56 if (offset < 0) 57 return false; 58 59 *target = *(unsigned long *)((void *)regs + offset); 60 61 return true; 62 } 63 64 /* 65 * Checks if a ud2 trap is because of a CFI failure, and handles the trap 66 * if needed. Returns a bug_trap_type value similarly to report_bug. 67 */ 68 enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) 69 { 70 unsigned long target, addr = regs->ip; 71 u32 type; 72 73 switch (cfi_mode) { 74 case CFI_KCFI: 75 if (!is_cfi_trap(addr)) { 76 /* 77 * The updated kCFI sequence has "test $0xd6, %al" instead of 78 * "ud2", adjust the offset. 79 */ 80 addr -= 1; 81 if (!is_cfi_trap(addr)) 82 return BUG_TRAP_TYPE_NONE; 83 } 84 85 if (!decode_cfi_insn(regs, &target, &type)) 86 return report_cfi_failure_noaddr(regs, addr); 87 88 break; 89 90 case CFI_FINEIBT: 91 if (!decode_fineibt_insn(regs, &target, &type)) 92 return BUG_TRAP_TYPE_NONE; 93 94 break; 95 96 default: 97 return BUG_TRAP_TYPE_NONE; 98 } 99 100 return report_cfi_failure(regs, addr, &target, type); 101 } 102 103 /* 104 * Ensure that __kcfi_typeid_ symbols are emitted for functions that may 105 * not be indirectly called with all configurations. 106 */ 107 __ADDRESSABLE(__memcpy) 108