subpage-prot.c

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/*
 * Copyright 2007-2008 Paul Mackerras, IBM Corp.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>

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

/*
 * Free all pages allocated for subpage protection maps and pointers.
 * Also makes sure that the subpage_prot_table structure is
 * reinitialized for the next user.
 */
void subpage_prot_free(struct mm_struct *mm)
{
    struct subpage_prot_table *spt = &mm->context.spt;
    unsigned long i, j, addr;
    u32 **p;

    for (i = 0; i < 4; ++i) {
        if (spt->low_prot[i]) {
            free_page((unsigned long)spt->low_prot[i]);
            spt->low_prot[i] = NULL;
        }
    }
    addr = 0;
    for (i = 0; i < 2; ++i) {
        p = spt->protptrs[i];
        if (!p)
            continue;
        spt->protptrs[i] = NULL;
        for (j = 0; j < SBP_L2_COUNT && addr < spt->maxaddr;
             ++j, addr += PAGE_SIZE)
            if (p[j])
                free_page((unsigned long)p[j]);
        free_page((unsigned long)p);
    }
    spt->maxaddr = 0;
}

void subpage_prot_init_new_context(struct mm_struct *mm)
{
    struct subpage_prot_table *spt = &mm->context.spt;

    memset(spt, 0, sizeof(*spt));
}

static void hpte_flush_range(struct mm_struct *mm, unsigned long addr,
                 int npages)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *pte;
    spinlock_t *ptl;

    pgd = pgd_offset(mm, addr);
    if (pgd_none(*pgd))
        return;
    pud = pud_offset(pgd, addr);
    if (pud_none(*pud))
        return;
    pmd = pmd_offset(pud, addr);
    if (pmd_none(*pmd))
        return;
    pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
    arch_enter_lazy_mmu_mode();
    for (; npages > 0; --npages) {
        pte_update(mm, addr, pte, 0, 0);
        addr += PAGE_SIZE;
        ++pte;
    }
    arch_leave_lazy_mmu_mode();
    pte_unmap_unlock(pte - 1, ptl);
}

/*
 * Clear the subpage protection map for an address range, allowing
 * all accesses that are allowed by the pte permissions.
 */
static void subpage_prot_clear(unsigned long addr, unsigned long len)
{
    struct mm_struct *mm = current->mm;
    struct subpage_prot_table *spt = &mm->context.spt;
    u32 **spm, *spp;
    unsigned long i;
    size_t nw;
    unsigned long next, limit;

    down_write(&mm->mmap_sem);
    limit = addr + len;
    if (limit > spt->maxaddr)
        limit = spt->maxaddr;
    for (; addr < limit; addr = next) {
        next = pmd_addr_end(addr, limit);
        if (addr < 0x100000000) {
            spm = spt->low_prot;
        } else {
            spm = spt->protptrs[addr >> SBP_L3_SHIFT];
            if (!spm)
                continue;
        }
        spp = spm[(addr >> SBP_L2_SHIFT) & (SBP_L2_COUNT - 1)];
        if (!spp)
            continue;
        spp += (addr >> PAGE_SHIFT) & (SBP_L1_COUNT - 1);

        i = (addr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
        nw = PTRS_PER_PTE - i;
        if (addr + (nw << PAGE_SHIFT) > next)
            nw = (next - addr) >> PAGE_SHIFT;

        memset(spp, 0, nw * sizeof(u32));

        /* now flush any existing HPTEs for the range */
        hpte_flush_range(mm, addr, nw);
    }
    up_write(&mm->mmap_sem);
}

/*
 * Copy in a subpage protection map for an address range.
 * The map has 2 bits per 4k subpage, so 32 bits per 64k page.
 * Each 2-bit field is 0 to allow any access, 1 to prevent writes,
 * 2 or 3 to prevent all accesses.
 * Note that the normal page protections also apply; the subpage
 * protection mechanism is an additional constraint, so putting 0
 * in a 2-bit field won't allow writes to a page that is otherwise
 * write-protected.
 */
long sys_subpage_prot(unsigned long addr, unsigned long len, u32 __user *map)
{
    struct mm_struct *mm = current->mm;
    struct subpage_prot_table *spt = &mm->context.spt;
    u32 **spm, *spp;
    unsigned long i;
    size_t nw;
    unsigned long next, limit;
    int err;

    /* Check parameters */
    if ((addr & ~PAGE_MASK) || (len & ~PAGE_MASK) ||
        addr >= TASK_SIZE || len >= TASK_SIZE || addr + len > TASK_SIZE)
        return -EINVAL;

    if (is_hugepage_only_range(mm, addr, len))
        return -EINVAL;

    if (!map) {
        /* Clear out the protection map for the address range */
        subpage_prot_clear(addr, len);
        return 0;
    }

    if (!access_ok(VERIFY_READ, map, (len >> PAGE_SHIFT) * sizeof(u32)))
        return -EFAULT;

    down_write(&mm->mmap_sem);
    for (limit = addr + len; addr < limit; addr = next) {
        next = pmd_addr_end(addr, limit);
        err = -ENOMEM;
        if (addr < 0x100000000) {
            spm = spt->low_prot;
        } else {
            spm = spt->protptrs[addr >> SBP_L3_SHIFT];
            if (!spm) {
                spm = (u32 **)get_zeroed_page(GFP_KERNEL);
                if (!spm)
                    goto out;
                spt->protptrs[addr >> SBP_L3_SHIFT] = spm;
            }
        }
        spm += (addr >> SBP_L2_SHIFT) & (SBP_L2_COUNT - 1);
        spp = *spm;
        if (!spp) {
            spp = (u32 *)get_zeroed_page(GFP_KERNEL);
            if (!spp)
                goto out;
            *spm = spp;
        }
        spp += (addr >> PAGE_SHIFT) & (SBP_L1_COUNT - 1);

        local_irq_disable();
        demote_segment_4k(mm, addr);
        local_irq_enable();

        i = (addr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
        nw = PTRS_PER_PTE - i;
        if (addr + (nw << PAGE_SHIFT) > next)
            nw = (next - addr) >> PAGE_SHIFT;

        up_write(&mm->mmap_sem);
        err = -EFAULT;
        if (__copy_from_user(spp, map, nw * sizeof(u32)))
            goto out2;
        map += nw;
        down_write(&mm->mmap_sem);

        /* now flush any existing HPTEs for the range */
        hpte_flush_range(mm, addr, nw);
    }
    if (limit > spt->maxaddr)
        spt->maxaddr = limit;
    err = 0;
 out:
    up_write(&mm->mmap_sem);
 out2:
    return err;
}