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78 lines
1.8 KiB
C
78 lines
1.8 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Clang Control Flow Integrity (CFI) support.
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*
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* Copyright (C) 2023 Google LLC
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*/
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#include <asm/cfi.h>
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#include <asm/insn.h>
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/*
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* Returns the target address and the expected type when regs->epc points
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* to a compiler-generated CFI trap.
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*/
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static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
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u32 *type)
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{
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unsigned long *regs_ptr = (unsigned long *)regs;
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int rs1_num;
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u32 insn;
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*target = *type = 0;
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/*
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* The compiler generates the following instruction sequence
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* for indirect call checks:
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*
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* lw t1, -4(<reg>)
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* lui t2, <hi20>
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* addiw t2, t2, <lo12>
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* beq t1, t2, .Ltmp1
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* ebreak ; <- regs->epc
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* .Ltmp1:
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* jalr <reg>
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*
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* We can read the expected type and the target address from the
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* registers passed to the beq/jalr instructions.
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*/
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if (get_kernel_nofault(insn, (void *)regs->epc - 4))
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return false;
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if (!riscv_insn_is_beq(insn))
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return false;
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*type = (u32)regs_ptr[RV_EXTRACT_RS1_REG(insn)];
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if (get_kernel_nofault(insn, (void *)regs->epc) ||
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get_kernel_nofault(insn, (void *)regs->epc + GET_INSN_LENGTH(insn)))
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return false;
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if (riscv_insn_is_jalr(insn))
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rs1_num = RV_EXTRACT_RS1_REG(insn);
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else if (riscv_insn_is_c_jalr(insn))
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rs1_num = RVC_EXTRACT_C2_RS1_REG(insn);
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else
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return false;
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*target = regs_ptr[rs1_num];
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return true;
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}
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/*
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* Checks if the ebreak trap is because of a CFI failure, and handles the trap
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* if needed. Returns a bug_trap_type value similarly to report_bug.
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*/
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enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)
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{
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unsigned long target;
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u32 type;
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if (!is_cfi_trap(regs->epc))
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return BUG_TRAP_TYPE_NONE;
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if (!decode_cfi_insn(regs, &target, &type))
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return report_cfi_failure_noaddr(regs, regs->epc);
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return report_cfi_failure(regs, regs->epc, &target, type);
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}
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