// SPDX-License-Identifier: GPL-2.0 /* * Clang Control Flow Integrity (CFI) support. * * Copyright (C) 2022 Google LLC */ #include <linux/string.h> #include <linux/cfi.h> #include <asm/insn.h> #include <asm/insn-eval.h> /* * Returns the target address and the expected type when regs->ip points * to a compiler-generated CFI trap. */ static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target, u32 *type) { char buffer[MAX_INSN_SIZE]; struct insn insn; int offset = 0; *target = *type = 0; /* * The compiler generates the following instruction sequence * for indirect call checks: * * movl -<id>, %r10d ; 6 bytes * addl -4(%reg), %r10d ; 4 bytes * je .Ltmp1 ; 2 bytes * ud2 ; <- regs->ip * .Ltmp1: * * We can decode the expected type and the target address from the * movl/addl instructions. */ if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 12, MAX_INSN_SIZE)) return false; if (insn_decode_kernel(&insn, &buffer[offset])) return false; if (insn.opcode.value != 0xBA) return false; *type = -(u32)insn.immediate.value; if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 6, MAX_INSN_SIZE)) return false; if (insn_decode_kernel(&insn, &buffer[offset])) return false; if (insn.opcode.value != 0x3) return false; /* Read the target address from the register. */ offset = insn_get_modrm_rm_off(&insn, regs); if (offset < 0) return false; *target = *(unsigned long *)((void *)regs + offset); return true; } /* * Checks if a ud2 trap is because of a CFI failure, and handles the trap * if needed. Returns a bug_trap_type value similarly to report_bug. */ enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) { unsigned long target, addr = regs->ip; u32 type; switch (cfi_mode) { case CFI_KCFI: if (!is_cfi_trap(addr)) return BUG_TRAP_TYPE_NONE; if (!decode_cfi_insn(regs, &target, &type)) return report_cfi_failure_noaddr(regs, addr); break; case CFI_FINEIBT: if (!decode_fineibt_insn(regs, &target, &type)) return BUG_TRAP_TYPE_NONE; break; default: return BUG_TRAP_TYPE_NONE; } return report_cfi_failure(regs, addr, &target, type); } /* * Ensure that __kcfi_typeid_ symbols are emitted for functions that may * not be indirectly called with all configurations. */ __ADDRESSABLE(__memcpy)