1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Clang Control Flow Integrity (CFI) support. 4 * 5 * Copyright (C) 2023 Google LLC 6 */ 7 #include <asm/cfi.h> 8 #include <asm/insn.h> 9 10 /* 11 * Returns the target address and the expected type when regs->epc points 12 * to a compiler-generated CFI trap. 13 */ 14 static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target, 15 u32 *type) 16 { 17 unsigned long *regs_ptr = (unsigned long *)regs; 18 int rs1_num; 19 u32 insn; 20 21 *target = *type = 0; 22 23 /* 24 * The compiler generates the following instruction sequence 25 * for indirect call checks: 26 * 27 * lw t1, -4(<reg>) 28 * lui t2, <hi20> 29 * addiw t2, t2, <lo12> 30 * beq t1, t2, .Ltmp1 31 * ebreak ; <- regs->epc 32 * .Ltmp1: 33 * jalr <reg> 34 * 35 * We can read the expected type and the target address from the 36 * registers passed to the beq/jalr instructions. 37 */ 38 if (get_kernel_nofault(insn, (void *)regs->epc - 4)) 39 return false; 40 if (!riscv_insn_is_beq(insn)) 41 return false; 42 43 *type = (u32)regs_ptr[RV_EXTRACT_RS1_REG(insn)]; 44 45 if (get_kernel_nofault(insn, (void *)regs->epc) || 46 get_kernel_nofault(insn, (void *)regs->epc + GET_INSN_LENGTH(insn))) 47 return false; 48 49 if (riscv_insn_is_jalr(insn)) 50 rs1_num = RV_EXTRACT_RS1_REG(insn); 51 else if (riscv_insn_is_c_jalr(insn)) 52 rs1_num = RVC_EXTRACT_C2_RS1_REG(insn); 53 else 54 return false; 55 56 *target = regs_ptr[rs1_num]; 57 58 return true; 59 } 60 61 /* 62 * Checks if the ebreak trap is because of a CFI failure, and handles the trap 63 * if needed. Returns a bug_trap_type value similarly to report_bug. 64 */ 65 enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) 66 { 67 unsigned long target; 68 u32 type; 69 70 if (!is_cfi_trap(regs->epc)) 71 return BUG_TRAP_TYPE_NONE; 72 73 if (!decode_cfi_insn(regs, &target, &type)) 74 return report_cfi_failure_noaddr(regs, regs->epc); 75 76 return report_cfi_failure(regs, regs->epc, &target, type); 77 } 78