maccess.c

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/*
 * Access kernel memory without faulting -- s390 specific implementation.
 *
 * Copyright IBM Corp. 2009
 *
 *   Author(s): Heiko Carstens <[email protected]>,
 *
 */

#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/cpu.h>
#include <asm/ctl_reg.h>

/*
 * This function writes to kernel memory bypassing DAT and possible
 * write protection. It copies one to four bytes from src to dst
 * using the stura instruction.
 * Returns the number of bytes copied or -EFAULT.
 */
static long probe_kernel_write_odd(void *dst, const void *src, size_t size)
{
    unsigned long count, aligned;
    int offset, mask;
    int rc = -EFAULT;

    aligned = (unsigned long) dst & ~3UL;
    offset = (unsigned long) dst & 3;
    count = min_t(unsigned long, 4 - offset, size);
    mask = (0xf << (4 - count)) & 0xf;
    mask >>= offset;
    asm volatile(
        "   bras    1,0f\n"
        "   icm 0,0,0(%3)\n"
        "0: l   0,0(%1)\n"
        "   lra %1,0(%1)\n"
        "1: ex  %2,0(1)\n"
        "2: stura   0,%1\n"
        "   la  %0,0\n"
        "3:\n"
        EX_TABLE(0b,3b) EX_TABLE(1b,3b) EX_TABLE(2b,3b)
        : "+d" (rc), "+a" (aligned)
        : "a" (mask), "a" (src) : "cc", "memory", "0", "1");
    return rc ? rc : count;
}

long probe_kernel_write(void *dst, const void *src, size_t size)
{
    long copied = 0;

    while (size) {
        copied = probe_kernel_write_odd(dst, src, size);
        if (copied < 0)
            break;
        dst += copied;
        src += copied;
        size -= copied;
    }
    return copied < 0 ? -EFAULT : 0;
}

static int __memcpy_real(void *dest, void *src, size_t count)
{
    register unsigned long _dest asm("2") = (unsigned long) dest;
    register unsigned long _len1 asm("3") = (unsigned long) count;
    register unsigned long _src  asm("4") = (unsigned long) src;
    register unsigned long _len2 asm("5") = (unsigned long) count;
    int rc = -EFAULT;

    asm volatile (
        "0: mvcle   %1,%2,0x0\n"
        "1: jo  0b\n"
        "   lhi %0,0x0\n"
        "2:\n"
        EX_TABLE(1b,2b)
        : "+d" (rc), "+d" (_dest), "+d" (_src), "+d" (_len1),
          "+d" (_len2), "=m" (*((long *) dest))
        : "m" (*((long *) src))
        : "cc", "memory");
    return rc;
}

/*
 * Copy memory in real mode (kernel to kernel)
 */
int memcpy_real(void *dest, void *src, size_t count)
{
    unsigned long flags;
    int rc;

    if (!count)
        return 0;
    local_irq_save(flags);
    __arch_local_irq_stnsm(0xfbUL);
    rc = __memcpy_real(dest, src, count);
    local_irq_restore(flags);
    return rc;
}

/*
 * Copy memory in absolute mode (kernel to kernel)
 */
void memcpy_absolute(void *dest, void *src, size_t count)
{
    unsigned long cr0, flags, prefix;

    flags = arch_local_irq_save();
    __ctl_store(cr0, 0, 0);
    __ctl_clear_bit(0, 28); /* disable lowcore protection */
    prefix = store_prefix();
    if (prefix) {
        local_mcck_disable();
        set_prefix(0);
        memcpy(dest, src, count);
        set_prefix(prefix);
        local_mcck_enable();
    } else {
        memcpy(dest, src, count);
    }
    __ctl_load(cr0, 0, 0);
    arch_local_irq_restore(flags);
}

/*
 * Copy memory from kernel (real) to user (virtual)
 */
int copy_to_user_real(void __user *dest, void *src, size_t count)
{
    int offs = 0, size, rc;
    char *buf;

    buf = (char *) __get_free_page(GFP_KERNEL);
    if (!buf)
        return -ENOMEM;
    rc = -EFAULT;
    while (offs < count) {
        size = min(PAGE_SIZE, count - offs);
        if (memcpy_real(buf, src + offs, size))
            goto out;
        if (copy_to_user(dest + offs, buf, size))
            goto out;
        offs += size;
    }
    rc = 0;
out:
    free_page((unsigned long) buf);
    return rc;
}

/*
 * Copy memory from user (virtual) to kernel (real)
 */
int copy_from_user_real(void *dest, void __user *src, size_t count)
{
    int offs = 0, size, rc;
    char *buf;

    buf = (char *) __get_free_page(GFP_KERNEL);
    if (!buf)
        return -ENOMEM;
    rc = -EFAULT;
    while (offs < count) {
        size = min(PAGE_SIZE, count - offs);
        if (copy_from_user(buf, src + offs, size))
            goto out;
        if (memcpy_real(dest + offs, buf, size))
            goto out;
        offs += size;
    }
    rc = 0;
out:
    free_page((unsigned long) buf);
    return rc;
}

/*
 * Check if physical address is within prefix or zero page
 */
static int is_swapped(unsigned long addr)
{
    unsigned long lc;
    int cpu;

    if (addr < sizeof(struct _lowcore))
        return 1;
    for_each_online_cpu(cpu) {
        lc = (unsigned long) lowcore_ptr[cpu];
        if (addr > lc + sizeof(struct _lowcore) - 1 || addr < lc)
            continue;
        return 1;
    }
    return 0;
}

/*
 * Convert a physical pointer for /dev/mem access
 *
 * For swapped prefix pages a new buffer is returned that contains a copy of
 * the absolute memory. The buffer size is maximum one page large.
 */
void *xlate_dev_mem_ptr(unsigned long addr)
{
    void *bounce = (void *) addr;
    unsigned long size;

    get_online_cpus();
    preempt_disable();
    if (is_swapped(addr)) {
        size = PAGE_SIZE - (addr & ~PAGE_MASK);
        bounce = (void *) __get_free_page(GFP_ATOMIC);
        if (bounce)
            memcpy_absolute(bounce, (void *) addr, size);
    }
    preempt_enable();
    put_online_cpus();
    return bounce;
}

/*
 * Free converted buffer for /dev/mem access (if necessary)
 */
void unxlate_dev_mem_ptr(unsigned long addr, void *buf)
{
    if ((void *) addr != buf)
        free_page((unsigned long) buf);
}