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// 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;
u32 type;
if (!is_cfi_trap(regs->ip))
return BUG_TRAP_TYPE_NONE;
if (!decode_cfi_insn(regs, &target, &type))
return report_cfi_failure_noaddr(regs, regs->ip);
return report_cfi_failure(regs, regs->ip, &target, type);
}
/*
* Ensure that __kcfi_typeid_ symbols are emitted for functions that may
* not be indirectly called with all configurations.
*/
__ADDRESSABLE(__memcpy)
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