mmu.c

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/*
 * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <asm/pgalloc.h>
#include <asm/pgtable.h>
#include <as-layout.h>
#include <os.h>
#include <skas.h>

extern int __syscall_stub_start;

static int init_stub_pte(struct mm_struct *mm, unsigned long proc,
             unsigned long kernel)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *pte;

    pgd = pgd_offset(mm, proc);
    pud = pud_alloc(mm, pgd, proc);
    if (!pud)
        goto out;

    pmd = pmd_alloc(mm, pud, proc);
    if (!pmd)
        goto out_pmd;

    pte = pte_alloc_map(mm, NULL, pmd, proc);
    if (!pte)
        goto out_pte;

    *pte = mk_pte(virt_to_page(kernel), __pgprot(_PAGE_PRESENT));
    *pte = pte_mkread(*pte);
    return 0;

 out_pte:
    pmd_free(mm, pmd);
 out_pmd:
    pud_free(mm, pud);
 out:
    return -ENOMEM;
}

int init_new_context(struct task_struct *task, struct mm_struct *mm)
{
    struct mm_context *from_mm = NULL;
    struct mm_context *to_mm = &mm->context;
    unsigned long stack = 0;
    int ret = -ENOMEM;

    if (skas_needs_stub) {
        stack = get_zeroed_page(GFP_KERNEL);
        if (stack == 0)
            goto out;
    }

    to_mm->id.stack = stack;
    if (current->mm != NULL && current->mm != &init_mm)
        from_mm = &current->mm->context;

    if (proc_mm) {
        ret = new_mm(stack);
        if (ret < 0) {
            printk(KERN_ERR "init_new_context_skas - "
                   "new_mm failed, errno = %d\n", ret);
            goto out_free;
        }
        to_mm->id.u.mm_fd = ret;
    }
    else {
        if (from_mm)
            to_mm->id.u.pid = copy_context_skas0(stack,
                                 from_mm->id.u.pid);
        else to_mm->id.u.pid = start_userspace(stack);

        if (to_mm->id.u.pid < 0) {
            ret = to_mm->id.u.pid;
            goto out_free;
        }
    }

    ret = init_new_ldt(to_mm, from_mm);
    if (ret < 0) {
        printk(KERN_ERR "init_new_context_skas - init_ldt"
               " failed, errno = %d\n", ret);
        goto out_free;
    }

    return 0;

 out_free:
    if (to_mm->id.stack != 0)
        free_page(to_mm->id.stack);
 out:
    return ret;
}

void uml_setup_stubs(struct mm_struct *mm)
{
    int err, ret;

    if (!skas_needs_stub)
        return;

    ret = init_stub_pte(mm, STUB_CODE,
                (unsigned long) &__syscall_stub_start);
    if (ret)
        goto out;

    ret = init_stub_pte(mm, STUB_DATA, mm->context.id.stack);
    if (ret)
        goto out;

    mm->context.stub_pages[0] = virt_to_page(&__syscall_stub_start);
    mm->context.stub_pages[1] = virt_to_page(mm->context.id.stack);

    /* dup_mmap already holds mmap_sem */
    err = install_special_mapping(mm, STUB_START, STUB_END - STUB_START,
                      VM_READ | VM_MAYREAD | VM_EXEC |
                      VM_MAYEXEC | VM_DONTCOPY,
                      mm->context.stub_pages);
    if (err) {
        printk(KERN_ERR "install_special_mapping returned %d\n", err);
        goto out;
    }
    return;

out:
    force_sigsegv(SIGSEGV, current);
}

void arch_exit_mmap(struct mm_struct *mm)
{
    pte_t *pte;

    pte = virt_to_pte(mm, STUB_CODE);
    if (pte != NULL)
        pte_clear(mm, STUB_CODE, pte);

    pte = virt_to_pte(mm, STUB_DATA);
    if (pte == NULL)
        return;

    pte_clear(mm, STUB_DATA, pte);
}

void destroy_context(struct mm_struct *mm)
{
    struct mm_context *mmu = &mm->context;

    if (proc_mm)
        os_close_file(mmu->id.u.mm_fd);
    else {
        /*
         * If init_new_context wasn't called, this will be
         * zero, resulting in a kill(0), which will result in the
         * whole UML suddenly dying.  Also, cover negative and
         * 1 cases, since they shouldn't happen either.
         */
        if (mmu->id.u.pid < 2) {
            printk(KERN_ERR "corrupt mm_context - pid = %d\n",
                   mmu->id.u.pid);
            return;
        }
        os_kill_ptraced_process(mmu->id.u.pid, 1);
    }

    if (skas_needs_stub)
        free_page(mmu->id.stack);

    free_ldt(mmu);
}