HOME

/**
@file     write_protection.h
@brief    Disable/Enable write protection
@details  Copyright (c) 2024 Acronis International GmbH
@author   Denis Kopyrin (Denis.Kopyrin@acronis.com)
@since    $Id: $
*/

#pragma once

#include "compat.h"

#ifndef X86_CR4_CET
# define X86_CR4_CET (1UL << 23)
#endif

#ifndef __FORCE_ORDER
# define __FORCE_ORDER "m"(*(unsigned int *)0x1000UL)
#endif

static inline unsigned long fp_read_cr4(void) {
#ifndef KERNEL_MOCK
	// cr4 is protected register in userspace
	unsigned long val;
	asm volatile("mov %%cr4, %0\n" : "=r" (val) : __FORCE_ORDER);
	return val;
#else
	return gCR4;
#endif
}

static inline void fp_write_cr4(unsigned long val) {
#ifndef KERNEL_MOCK
		// cr0 is protected register in userspace
	asm volatile("mov %0, %%cr4\n": "+r" (val) : : "memory");
#else
	gCR4 = val;
#endif
}

// On 5.3.0 using the legal 'write_cp0' causes panic because WP is not disabled.
// So let's just use out own 'write_cp0' that avoid silly checks.
static inline void wp_cr0(unsigned long cr0)
{
#ifndef KERNEL_MOCK
	// cr0 is protected register in userspace
	__asm__ __volatile__ ("mov %0, %%cr0": "+r"(cr0));
#else
	gCR0 = cr0;
#endif
}

typedef struct {
	unsigned long saved_cr0;
	unsigned long written_cr0;
	unsigned long saved_cr4;
	unsigned long written_cr4;
	bool was_written_cr0;
	bool was_written_cr4;
} cr0_write_protect_t;

static inline cr0_write_protect_t disable_write_protect(void)
{
	cr0_write_protect_t wp;

	wp.saved_cr0 = read_cr0();
	wp.saved_cr4 = fp_read_cr4();
	wp.written_cr0 = wp.saved_cr0;
	wp.written_cr4 = wp.saved_cr4;
	wp.was_written_cr0 = false;
	wp.was_written_cr4 = false;
	if (wp.saved_cr4 & X86_CR4_CET) {
		wp.was_written_cr4 = true;
		wp.written_cr4 &= ~X86_CR4_CET;
		fp_write_cr4(wp.written_cr4);
	}
	if (wp.saved_cr0 & X86_CR0_WP) {
		wp.was_written_cr0 = true;
		wp.written_cr0 &= ~X86_CR0_WP;
		wp_cr0(wp.written_cr0);
	}

	return wp;
}

static inline void restore_write_protect(cr0_write_protect_t wp)
{
	if (wp.was_written_cr0)
		wp_cr0(wp.saved_cr0);
	if (wp.was_written_cr4)
		fp_write_cr4(wp.saved_cr4);
}

static inline void redisable_write_protect(cr0_write_protect_t wp)
{
	if (wp.was_written_cr4)
		fp_write_cr4(wp.written_cr4);
	if (wp.was_written_cr0)
		wp_cr0(wp.written_cr0);
}