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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_X86_CFI_H
#define _ASM_X86_CFI_H
/*
* Clang Control Flow Integrity (CFI) support.
*
* Copyright (C) 2022 Google LLC
*/
#include <linux/bug.h>
#include <asm/ibt.h>
/*
* An overview of the various calling conventions...
*
* Traditional:
*
* foo:
* ... code here ...
* ret
*
* direct caller:
* call foo
*
* indirect caller:
* lea foo(%rip), %r11
* ...
* call *%r11
*
*
* IBT:
*
* foo:
* endbr64
* ... code here ...
* ret
*
* direct caller:
* call foo / call foo+4
*
* indirect caller:
* lea foo(%rip), %r11
* ...
* call *%r11
*
*
* kCFI:
*
* __cfi_foo:
* movl $0x12345678, %eax
* # 11 nops when CONFIG_CALL_PADDING
* foo:
* endbr64 # when IBT
* ... code here ...
* ret
*
* direct call:
* call foo # / call foo+4 when IBT
*
* indirect call:
* lea foo(%rip), %r11
* ...
* movl $(-0x12345678), %r10d
* addl -4(%r11), %r10d # -15 when CONFIG_CALL_PADDING
* jz 1f
* ud2
* 1:call *%r11
*
*
* FineIBT (builds as kCFI + CALL_PADDING + IBT + RETPOLINE and runtime patches into):
*
* __cfi_foo:
* endbr64
* subl 0x12345678, %r10d
* jz foo
* ud2
* nop
* foo:
* osp nop3 # was endbr64
* ... code here ...
* ret
*
* direct caller:
* call foo / call foo+4
*
* indirect caller:
* lea foo(%rip), %r11
* ...
* movl $0x12345678, %r10d
* subl $16, %r11
* nop4
* call *%r11
*
*/
enum cfi_mode {
CFI_AUTO, /* FineIBT if hardware has IBT, otherwise kCFI */
CFI_OFF, /* Taditional / IBT depending on .config */
CFI_KCFI, /* Optionally CALL_PADDING, IBT, RETPOLINE */
CFI_FINEIBT, /* see arch/x86/kernel/alternative.c */
};
extern enum cfi_mode cfi_mode;
struct pt_regs;
#ifdef CONFIG_CFI_CLANG
enum bug_trap_type handle_cfi_failure(struct pt_regs *regs);
#define __bpfcall
extern u32 cfi_bpf_hash;
extern u32 cfi_bpf_subprog_hash;
static inline int cfi_get_offset(void)
{
switch (cfi_mode) {
case CFI_FINEIBT:
return 16;
case CFI_KCFI:
if (IS_ENABLED(CONFIG_CALL_PADDING))
return 16;
return 5;
default:
return 0;
}
}
#define cfi_get_offset cfi_get_offset
extern u32 cfi_get_func_hash(void *func);
#else
static inline enum bug_trap_type handle_cfi_failure(struct pt_regs *regs)
{
return BUG_TRAP_TYPE_NONE;
}
#define cfi_bpf_hash 0U
#define cfi_bpf_subprog_hash 0U
static inline u32 cfi_get_func_hash(void *func)
{
return 0;
}
#endif /* CONFIG_CFI_CLANG */
#if HAS_KERNEL_IBT == 1
#define CFI_NOSEAL(x) asm(IBT_NOSEAL(__stringify(x)))
#endif
#endif /* _ASM_X86_CFI_H */
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