| 1 | |
| 2 | |
| 3 | * Clang Control Flow Integrity (CFI) support.
|
| 4 | *
|
| 5 | * Copyright (C) 2023 Google LLC
|
| 6 |
|
| 7 | #include <linux/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 | }
|