vdso.c

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/*
 * vdso setup for s390
 *
 *  Copyright IBM Corp. 2008
 *  Author(s): Martin Schwidefsky ([email protected])
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License (version 2 only)
 * as published by the Free Software Foundation.
 */

#include <linux/module.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/slab.h>
#include <linux/user.h>
#include <linux/elf.h>
#include <linux/security.h>
#include <linux/bootmem.h>
#include <linux/compat.h>
#include <asm/asm-offsets.h>
#include <asm/pgtable.h>
#include <asm/processor.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
#include <asm/sections.h>
#include <asm/vdso.h>
#include <asm/facility.h>

#if defined(CONFIG_32BIT) || defined(CONFIG_COMPAT)
extern char vdso32_start, vdso32_end;
static void *vdso32_kbase = &vdso32_start;
static unsigned int vdso32_pages;
static struct page **vdso32_pagelist;
#endif

#ifdef CONFIG_64BIT
extern char vdso64_start, vdso64_end;
static void *vdso64_kbase = &vdso64_start;
static unsigned int vdso64_pages;
static struct page **vdso64_pagelist;
#endif /* CONFIG_64BIT */

/*
 * Should the kernel map a VDSO page into processes and pass its
 * address down to glibc upon exec()?
 */
unsigned int __read_mostly vdso_enabled = 1;

static int __init vdso_setup(char *s)
{
    unsigned long val;
    int rc;

    rc = 0;
    if (strncmp(s, "on", 3) == 0)
        vdso_enabled = 1;
    else if (strncmp(s, "off", 4) == 0)
        vdso_enabled = 0;
    else {
        rc = strict_strtoul(s, 0, &val);
        vdso_enabled = rc ? 0 : !!val;
    }
    return !rc;
}
__setup("vdso=", vdso_setup);

/*
 * The vdso data page
 */
static union {
    struct vdso_data    data;
    u8          page[PAGE_SIZE];
} vdso_data_store __page_aligned_data;
struct vdso_data *vdso_data = &vdso_data_store.data;

/*
 * Setup vdso data page.
 */
static void vdso_init_data(struct vdso_data *vd)
{
    vd->ectg_available =
        s390_user_mode != HOME_SPACE_MODE && test_facility(31);
}

#ifdef CONFIG_64BIT
/*
 * Allocate/free per cpu vdso data.
 */
#define SEGMENT_ORDER   2

int vdso_alloc_per_cpu(struct _lowcore *lowcore)
{
    unsigned long segment_table, page_table, page_frame;
    u32 *psal, *aste;
    int i;

    lowcore->vdso_per_cpu_data = __LC_PASTE;

    if (s390_user_mode == HOME_SPACE_MODE || !vdso_enabled)
        return 0;

    segment_table = __get_free_pages(GFP_KERNEL, SEGMENT_ORDER);
    page_table = get_zeroed_page(GFP_KERNEL | GFP_DMA);
    page_frame = get_zeroed_page(GFP_KERNEL);
    if (!segment_table || !page_table || !page_frame)
        goto out;

    clear_table((unsigned long *) segment_table, _SEGMENT_ENTRY_EMPTY,
            PAGE_SIZE << SEGMENT_ORDER);
    clear_table((unsigned long *) page_table, _PAGE_TYPE_EMPTY,
            256*sizeof(unsigned long));

    *(unsigned long *) segment_table = _SEGMENT_ENTRY + page_table;
    *(unsigned long *) page_table = _PAGE_RO + page_frame;

    psal = (u32 *) (page_table + 256*sizeof(unsigned long));
    aste = psal + 32;

    for (i = 4; i < 32; i += 4)
        psal[i] = 0x80000000;

    lowcore->paste[4] = (u32)(addr_t) psal;
    psal[0] = 0x20000000;
    psal[2] = (u32)(addr_t) aste;
    *(unsigned long *) (aste + 2) = segment_table +
        _ASCE_TABLE_LENGTH + _ASCE_USER_BITS + _ASCE_TYPE_SEGMENT;
    aste[4] = (u32)(addr_t) psal;
    lowcore->vdso_per_cpu_data = page_frame;

    return 0;

out:
    free_page(page_frame);
    free_page(page_table);
    free_pages(segment_table, SEGMENT_ORDER);
    return -ENOMEM;
}

void vdso_free_per_cpu(struct _lowcore *lowcore)
{
    unsigned long segment_table, page_table, page_frame;
    u32 *psal, *aste;

    if (s390_user_mode == HOME_SPACE_MODE || !vdso_enabled)
        return;

    psal = (u32 *)(addr_t) lowcore->paste[4];
    aste = (u32 *)(addr_t) psal[2];
    segment_table = *(unsigned long *)(aste + 2) & PAGE_MASK;
    page_table = *(unsigned long *) segment_table;
    page_frame = *(unsigned long *) page_table;

    free_page(page_frame);
    free_page(page_table);
    free_pages(segment_table, SEGMENT_ORDER);
}

static void vdso_init_cr5(void)
{
    unsigned long cr5;

    if (s390_user_mode == HOME_SPACE_MODE || !vdso_enabled)
        return;
    cr5 = offsetof(struct _lowcore, paste);
    __ctl_load(cr5, 5, 5);
}
#endif /* CONFIG_64BIT */

/*
 * This is called from binfmt_elf, we create the special vma for the
 * vDSO and insert it into the mm struct tree
 */
int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
{
    struct mm_struct *mm = current->mm;
    struct page **vdso_pagelist;
    unsigned long vdso_pages;
    unsigned long vdso_base;
    int rc;

    if (!vdso_enabled)
        return 0;
    /*
     * Only map the vdso for dynamically linked elf binaries.
     */
    if (!uses_interp)
        return 0;

#ifdef CONFIG_64BIT
    vdso_pagelist = vdso64_pagelist;
    vdso_pages = vdso64_pages;
#ifdef CONFIG_COMPAT
    if (is_compat_task()) {
        vdso_pagelist = vdso32_pagelist;
        vdso_pages = vdso32_pages;
    }
#endif
#else
    vdso_pagelist = vdso32_pagelist;
    vdso_pages = vdso32_pages;
#endif

    /*
     * vDSO has a problem and was disabled, just don't "enable" it for
     * the process
     */
    if (vdso_pages == 0)
        return 0;

    current->mm->context.vdso_base = 0;

    /*
     * pick a base address for the vDSO in process space. We try to put
     * it at vdso_base which is the "natural" base for it, but we might
     * fail and end up putting it elsewhere.
     */
    down_write(&mm->mmap_sem);
    vdso_base = get_unmapped_area(NULL, 0, vdso_pages << PAGE_SHIFT, 0, 0);
    if (IS_ERR_VALUE(vdso_base)) {
        rc = vdso_base;
        goto out_up;
    }

    /*
     * Put vDSO base into mm struct. We need to do this before calling
     * install_special_mapping or the perf counter mmap tracking code
     * will fail to recognise it as a vDSO (since arch_vma_name fails).
     */
    current->mm->context.vdso_base = vdso_base;

    /*
     * our vma flags don't have VM_WRITE so by default, the process
     * isn't allowed to write those pages.
     * gdb can break that with ptrace interface, and thus trigger COW
     * on those pages but it's then your responsibility to never do that
     * on the "data" page of the vDSO or you'll stop getting kernel
     * updates and your nice userland gettimeofday will be totally dead.
     * It's fine to use that for setting breakpoints in the vDSO code
     * pages though.
     */
    rc = install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
                     VM_READ|VM_EXEC|
                     VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
                     vdso_pagelist);
    if (rc)
        current->mm->context.vdso_base = 0;
out_up:
    up_write(&mm->mmap_sem);
    return rc;
}

const char *arch_vma_name(struct vm_area_struct *vma)
{
    if (vma->vm_mm && vma->vm_start == vma->vm_mm->context.vdso_base)
        return "[vdso]";
    return NULL;
}

static int __init vdso_init(void)
{
    int i;

    if (!vdso_enabled)
        return 0;
    vdso_init_data(vdso_data);
#if defined(CONFIG_32BIT) || defined(CONFIG_COMPAT)
    /* Calculate the size of the 32 bit vDSO */
    vdso32_pages = ((&vdso32_end - &vdso32_start
             + PAGE_SIZE - 1) >> PAGE_SHIFT) + 1;

    /* Make sure pages are in the correct state */
    vdso32_pagelist = kzalloc(sizeof(struct page *) * (vdso32_pages + 1),
                  GFP_KERNEL);
    BUG_ON(vdso32_pagelist == NULL);
    for (i = 0; i < vdso32_pages - 1; i++) {
        struct page *pg = virt_to_page(vdso32_kbase + i*PAGE_SIZE);
        ClearPageReserved(pg);
        get_page(pg);
        vdso32_pagelist[i] = pg;
    }
    vdso32_pagelist[vdso32_pages - 1] = virt_to_page(vdso_data);
    vdso32_pagelist[vdso32_pages] = NULL;
#endif

#ifdef CONFIG_64BIT
    /* Calculate the size of the 64 bit vDSO */
    vdso64_pages = ((&vdso64_end - &vdso64_start
             + PAGE_SIZE - 1) >> PAGE_SHIFT) + 1;

    /* Make sure pages are in the correct state */
    vdso64_pagelist = kzalloc(sizeof(struct page *) * (vdso64_pages + 1),
                  GFP_KERNEL);
    BUG_ON(vdso64_pagelist == NULL);
    for (i = 0; i < vdso64_pages - 1; i++) {
        struct page *pg = virt_to_page(vdso64_kbase + i*PAGE_SIZE);
        ClearPageReserved(pg);
        get_page(pg);
        vdso64_pagelist[i] = pg;
    }
    vdso64_pagelist[vdso64_pages - 1] = virt_to_page(vdso_data);
    vdso64_pagelist[vdso64_pages] = NULL;
    if (vdso_alloc_per_cpu(&S390_lowcore))
        BUG();
    vdso_init_cr5();
#endif /* CONFIG_64BIT */

    get_page(virt_to_page(vdso_data));

    smp_wmb();

    return 0;
}
early_initcall(vdso_init);

int in_gate_area_no_mm(unsigned long addr)
{
    return 0;
}

int in_gate_area(struct mm_struct *mm, unsigned long addr)
{
    return 0;
}

struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
{
    return NULL;
}