/*
 * 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/set_memory.h>
#include <asm/tlbflush.h>

struct page_change_data {
        pgprot_t set_mask;
        pgprot_t clear_mask;
};

bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED);

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

        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;

        /*
         * If we are manipulating read-only permissions, apply the same
         * change to the linear mapping of the pages that back this VM area.
         */
        if (rodata_full && (pgprot_val(set_mask) == PTE_RDONLY ||
                            pgprot_val(clear_mask) == PTE_RDONLY)) {
                for (i = 0; i < area->nr_pages; i++) {
                        __change_memory_common((u64)page_address(area->pages[i]),
                                               PAGE_SIZE, set_mask, clear_mask);
                }
        }

        /*
         * Get rid of potentially aliasing lazily unmapped vm areas that may
         * have permissions set that deviate from the ones we are setting here.
         */
        vm_unmap_aliases();

        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);

int set_memory_valid(unsigned long addr, int numpages, int enable)
{
        if (enable)
                return __change_memory_common(addr, PAGE_SIZE * numpages,
                                        __pgprot(PTE_VALID),
                                        __pgprot(0));
        else
                return __change_memory_common(addr, PAGE_SIZE * numpages,
                                        __pgprot(0),
                                        __pgprot(PTE_VALID));
}

int set_direct_map_invalid_noflush(struct page *page)
{
        struct page_change_data data = {
                .set_mask = __pgprot(0),
                .clear_mask = __pgprot(PTE_VALID),
        };

        if (!debug_pagealloc_enabled() && !rodata_full)
                return 0;

        return apply_to_page_range(&init_mm,
                                   (unsigned long)page_address(page),
                                   PAGE_SIZE, change_page_range, &data);
}

int set_direct_map_default_noflush(struct page *page)
{
        struct page_change_data data = {
                .set_mask = __pgprot(PTE_VALID | PTE_WRITE),
                .clear_mask = __pgprot(PTE_RDONLY),
        };

        if (!debug_pagealloc_enabled() && !rodata_full)
                return 0;

        return apply_to_page_range(&init_mm,
                                   (unsigned long)page_address(page),
                                   PAGE_SIZE, change_page_range, &data);
}

#ifdef CONFIG_DEBUG_PAGEALLOC
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
        if (!debug_pagealloc_enabled() && !rodata_full)
                return;

        set_memory_valid((unsigned long)page_address(page), numpages, enable);
}
#endif /* CONFIG_DEBUG_PAGEALLOC */

/*
 * This function is used to determine if a linear map page has been marked as
 * not-valid. Walk the page table and check the PTE_VALID bit. This is based
 * on kern_addr_valid(), which almost does what we need.
 *
 * Because this is only called on the kernel linear map,  p?d_sect() implies
 * p?d_present(). When debug_pagealloc is enabled, sections mappings are
 * disabled.
 */
bool kernel_page_present(struct page *page)
{
        pgd_t *pgdp;
        pud_t *pudp, pud;
        pmd_t *pmdp, pmd;
        pte_t *ptep;
        unsigned long addr = (unsigned long)page_address(page);

        if (!debug_pagealloc_enabled() && !rodata_full)
                return true;

        pgdp = pgd_offset_k(addr);
        if (pgd_none(READ_ONCE(*pgdp)))
                return false;

        pudp = pud_offset(pgdp, addr);
        pud = READ_ONCE(*pudp);
        if (pud_none(pud))
                return false;
        if (pud_sect(pud))
                return true;

        pmdp = pmd_offset(pudp, addr);
        pmd = READ_ONCE(*pmdp);
        if (pmd_none(pmd))
                return false;
        if (pmd_sect(pmd))
                return true;

        ptep = pte_offset_kernel(pmdp, addr);
        return pte_valid(READ_ONCE(*ptep));
}