vdso.c

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/*
 * VDSO implementation for AArch64 and vector page setup for AArch32.
 *
 * Copyright (C) 2012 ARM Limited
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Author: Will Deacon <[email protected]>
 */

#include <linux/kernel.h>
#include <linux/clocksource.h>
#include <linux/elf.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/signal.h>
#include <linux/slab.h>
#include <linux/timekeeper_internal.h>
#include <linux/vmalloc.h>

#include <asm/cacheflush.h>
#include <asm/signal32.h>
#include <asm/vdso.h>
#include <asm/vdso_datapage.h>

extern char vdso_start, vdso_end;
static unsigned long vdso_pages;
static struct page **vdso_pagelist;

/*
 * 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;

#ifdef CONFIG_COMPAT
/*
 * Create and map the vectors page for AArch32 tasks.
 */
static struct page *vectors_page[1];

static int alloc_vectors_page(void)
{
    extern char __kuser_helper_start[], __kuser_helper_end[];
    int kuser_sz = __kuser_helper_end - __kuser_helper_start;
    unsigned long vpage;

    vpage = get_zeroed_page(GFP_ATOMIC);

    if (!vpage)
        return -ENOMEM;

    /* kuser helpers */
    memcpy((void *)vpage + 0x1000 - kuser_sz, __kuser_helper_start,
        kuser_sz);

    /* sigreturn code */
    memcpy((void *)vpage + AARCH32_KERN_SIGRET_CODE_OFFSET,
        aarch32_sigret_code, sizeof(aarch32_sigret_code));

    flush_icache_range(vpage, vpage + PAGE_SIZE);
    vectors_page[0] = virt_to_page(vpage);

    return 0;
}
arch_initcall(alloc_vectors_page);

int aarch32_setup_vectors_page(struct linux_binprm *bprm, int uses_interp)
{
    struct mm_struct *mm = current->mm;
    unsigned long addr = AARCH32_VECTORS_BASE;
    int ret;

    down_write(&mm->mmap_sem);
    current->mm->context.vdso = (void *)addr;

    /* Map vectors page at the high address. */
    ret = install_special_mapping(mm, addr, PAGE_SIZE,
                      VM_READ|VM_EXEC|VM_MAYREAD|VM_MAYEXEC,
                      vectors_page);

    up_write(&mm->mmap_sem);

    return ret;
}
#endif /* CONFIG_COMPAT */

static int __init vdso_init(void)
{
    struct page *pg;
    char *vbase;
    int i, ret = 0;

    vdso_pages = (&vdso_end - &vdso_start) >> PAGE_SHIFT;
    pr_info("vdso: %ld pages (%ld code, %ld data) at base %p\n",
        vdso_pages + 1, vdso_pages, 1L, &vdso_start);

    /* Allocate the vDSO pagelist, plus a page for the data. */
    vdso_pagelist = kzalloc(sizeof(struct page *) * (vdso_pages + 1),
                GFP_KERNEL);
    if (vdso_pagelist == NULL) {
        pr_err("Failed to allocate vDSO pagelist!\n");
        return -ENOMEM;
    }

    /* Grab the vDSO code pages. */
    for (i = 0; i < vdso_pages; i++) {
        pg = virt_to_page(&vdso_start + i*PAGE_SIZE);
        ClearPageReserved(pg);
        get_page(pg);
        vdso_pagelist[i] = pg;
    }

    /* Sanity check the shared object header. */
    vbase = vmap(vdso_pagelist, 1, 0, PAGE_KERNEL);
    if (vbase == NULL) {
        pr_err("Failed to map vDSO pagelist!\n");
        return -ENOMEM;
    } else if (memcmp(vbase, "\177ELF", 4)) {
        pr_err("vDSO is not a valid ELF object!\n");
        ret = -EINVAL;
        goto unmap;
    }

    /* Grab the vDSO data page. */
    pg = virt_to_page(vdso_data);
    get_page(pg);
    vdso_pagelist[i] = pg;

unmap:
    vunmap(vbase);
    return ret;
}
arch_initcall(vdso_init);

int arch_setup_additional_pages(struct linux_binprm *bprm,
                int uses_interp)
{
    struct mm_struct *mm = current->mm;
    unsigned long vdso_base, vdso_mapping_len;
    int ret;

    /* Be sure to map the data page */
    vdso_mapping_len = (vdso_pages + 1) << PAGE_SHIFT;

    down_write(&mm->mmap_sem);
    vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
    if (IS_ERR_VALUE(vdso_base)) {
        ret = vdso_base;
        goto up_fail;
    }
    mm->context.vdso = (void *)vdso_base;

    ret = install_special_mapping(mm, vdso_base, vdso_mapping_len,
                      VM_READ|VM_EXEC|
                      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
                      vdso_pagelist);
    if (ret) {
        mm->context.vdso = NULL;
        goto up_fail;
    }

up_fail:
    up_write(&mm->mmap_sem);

    return ret;
}

const char *arch_vma_name(struct vm_area_struct *vma)
{
    /*
     * We can re-use the vdso pointer in mm_context_t for identifying
     * the vectors page for compat applications. The vDSO will always
     * sit above TASK_UNMAPPED_BASE and so we don't need to worry about
     * it conflicting with the vectors base.
     */
    if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso) {
#ifdef CONFIG_COMPAT
        if (vma->vm_start == AARCH32_VECTORS_BASE)
            return "[vectors]";
#endif
        return "[vdso]";
    }

    return NULL;
}

/*
 * We define AT_SYSINFO_EHDR, so we need these function stubs to keep
 * Linux happy.
 */
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;
}

/*
 * Update the vDSO data page to keep in sync with kernel timekeeping.
 */
void update_vsyscall(struct timekeeper *tk)
{
    struct timespec xtime_coarse;
    u32 use_syscall = strcmp(tk->clock->name, "arch_sys_counter");

    ++vdso_data->tb_seq_count;
    smp_wmb();

    xtime_coarse = __current_kernel_time();
    vdso_data->use_syscall          = use_syscall;
    vdso_data->xtime_coarse_sec     = xtime_coarse.tv_sec;
    vdso_data->xtime_coarse_nsec        = xtime_coarse.tv_nsec;

    if (!use_syscall) {
        vdso_data->cs_cycle_last    = tk->clock->cycle_last;
        vdso_data->xtime_clock_sec  = tk->xtime_sec;
        vdso_data->xtime_clock_nsec = tk->xtime_nsec >> tk->shift;
        vdso_data->cs_mult      = tk->mult;
        vdso_data->cs_shift     = tk->shift;
        vdso_data->wtm_clock_sec    = tk->wall_to_monotonic.tv_sec;
        vdso_data->wtm_clock_nsec   = tk->wall_to_monotonic.tv_nsec;
    }

    smp_wmb();
    ++vdso_data->tb_seq_count;
}

void update_vsyscall_tz(void)
{
    ++vdso_data->tb_seq_count;
    smp_wmb();
    vdso_data->tz_minuteswest   = sys_tz.tz_minuteswest;
    vdso_data->tz_dsttime       = sys_tz.tz_dsttime;
    smp_wmb();
    ++vdso_data->tb_seq_count;
}