pageattr.c

/*
 * Copyright (c) 2014, The Linux Foundation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 and
 * only version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/vmalloc.h>

#include <asm/pgtable.h>
#include <asm/tlbflush.h>

struct page_change_data {
	pgprot_t set_mask;
	pgprot_t clear_mask;
};

static int change_page_range(pte_t *ptep, pgtable_t token, unsigned long addr,
			void *data)
{
	struct page_change_data *cdata = data;
	pte_t pte = *ptep;

	pte = clear_pte_bit(pte, cdata->clear_mask);
	pte = set_pte_bit(pte, cdata->set_mask);

	set_pte(ptep, pte);
	return 0;
}

/*
 * This function assumes that the range is mapped with PAGE_SIZE pages.
 */
static int __change_memory_common(unsigned long start, unsigned long size,
				pgprot_t set_mask, pgprot_t clear_mask)
{
	struct page_change_data data;
	int ret;

	data.set_mask = set_mask;
	data.clear_mask = clear_mask;

	ret = apply_to_page_range(&init_mm, start, size, change_page_range,
					&data);

	flush_tlb_kernel_range(start, start + size);
	return ret;
}

static int change_memory_common(unsigned long addr, int numpages,
				pgprot_t set_mask, pgprot_t clear_mask)
{
	unsigned long start = addr;
	unsigned long size = PAGE_SIZE*numpages;
	unsigned long end = start + size;
	struct vm_struct *area;

	if (!PAGE_ALIGNED(addr)) {
		start &= PAGE_MASK;
		end = start + size;
		WARN_ON_ONCE(1);
	}

	/*
	 * Kernel VA mappings are always live, and splitting live section
	 * mappings into page mappings may cause TLB conflicts. This means
	 * we have to ensure that changing the permission bits of the range
	 * we are operating on does not result in such splitting.
	 *
	 * Let's restrict ourselves to mappings created by vmalloc (or vmap).
	 * Those are guaranteed to consist entirely of page mappings, and
	 * splitting is never needed.
	 *
	 * So check whether the [addr, addr + size) interval is entirely
	 * covered by precisely one VM area that has the VM_ALLOC flag set.
	 */
	area = find_vm_area((void *)addr);
	if (!area ||
	    end > (unsigned long)area->addr + area->size ||
	    !(area->flags & VM_ALLOC))
		return -EINVAL;

	if (!numpages)
		return 0;

	return __change_memory_common(start, size, set_mask, clear_mask);
}

int set_memory_ro(unsigned long addr, int numpages)
{
	return change_memory_common(addr, numpages,
					__pgprot(PTE_RDONLY),
					__pgprot(PTE_WRITE));
}

int set_memory_rw(unsigned long addr, int numpages)
{
	return change_memory_common(addr, numpages,
					__pgprot(PTE_WRITE),
					__pgprot(PTE_RDONLY));
}

int set_memory_nx(unsigned long addr, int numpages)
{
	return change_memory_common(addr, numpages,
					__pgprot(PTE_PXN),
					__pgprot(0));
}
EXPORT_SYMBOL_GPL(set_memory_nx);

int set_memory_x(unsigned long addr, int numpages)
{
	return change_memory_common(addr, numpages,
					__pgprot(0),
					__pgprot(PTE_PXN));
}
EXPORT_SYMBOL_GPL(set_memory_x);

#ifdef CONFIG_DEBUG_PAGEALLOC
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
	unsigned long addr = (unsigned long) page_address(page);

	if (enable)
		__change_memory_common(addr, PAGE_SIZE * numpages,
					__pgprot(PTE_VALID),
					__pgprot(0));
	else
		__change_memory_common(addr, PAGE_SIZE * numpages,
					__pgprot(0),
					__pgprot(PTE_VALID));
}
#endif