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