uaccess_pt.c

Go to the documentation of this file.

/*
 *  User access functions based on page table walks for enhanced
 *  system layout without hardware support.
 *
 *    Copyright IBM Corp. 2006, 2012
 *    Author(s): Gerald Schaefer ([email protected])
 */

#include <linux/errno.h>
#include <linux/hardirq.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <asm/uaccess.h>
#include <asm/futex.h>
#include "uaccess.h"


/*
 * Returns kernel address for user virtual address. If the returned address is
 * >= -4095 (IS_ERR_VALUE(x) returns true), a fault has occured and the address
 * contains the (negative) exception code.
 */
static __always_inline unsigned long follow_table(struct mm_struct *mm,
                          unsigned long addr, int write)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *ptep;

    pgd = pgd_offset(mm, addr);
    if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
        return -0x3aUL;

    pud = pud_offset(pgd, addr);
    if (pud_none(*pud) || unlikely(pud_bad(*pud)))
        return -0x3bUL;

    pmd = pmd_offset(pud, addr);
    if (pmd_none(*pmd))
        return -0x10UL;
    if (pmd_large(*pmd)) {
        if (write && (pmd_val(*pmd) & _SEGMENT_ENTRY_RO))
            return -0x04UL;
        return (pmd_val(*pmd) & HPAGE_MASK) + (addr & ~HPAGE_MASK);
    }
    if (unlikely(pmd_bad(*pmd)))
        return -0x10UL;

    ptep = pte_offset_map(pmd, addr);
    if (!pte_present(*ptep))
        return -0x11UL;
    if (write && !pte_write(*ptep))
        return -0x04UL;

    return (pte_val(*ptep) & PAGE_MASK) + (addr & ~PAGE_MASK);
}

static __always_inline size_t __user_copy_pt(unsigned long uaddr, void *kptr,
                         size_t n, int write_user)
{
    struct mm_struct *mm = current->mm;
    unsigned long offset, done, size, kaddr;
    void *from, *to;

    done = 0;
retry:
    spin_lock(&mm->page_table_lock);
    do {
        kaddr = follow_table(mm, uaddr, write_user);
        if (IS_ERR_VALUE(kaddr))
            goto fault;

        offset = uaddr & ~PAGE_MASK;
        size = min(n - done, PAGE_SIZE - offset);
        if (write_user) {
            to = (void *) kaddr;
            from = kptr + done;
        } else {
            from = (void *) kaddr;
            to = kptr + done;
        }
        memcpy(to, from, size);
        done += size;
        uaddr += size;
    } while (done < n);
    spin_unlock(&mm->page_table_lock);
    return n - done;
fault:
    spin_unlock(&mm->page_table_lock);
    if (__handle_fault(uaddr, -kaddr, write_user))
        return n - done;
    goto retry;
}

/*
 * Do DAT for user address by page table walk, return kernel address.
 * This function needs to be called with current->mm->page_table_lock held.
 */
static __always_inline unsigned long __dat_user_addr(unsigned long uaddr,
                             int write)
{
    struct mm_struct *mm = current->mm;
    unsigned long kaddr;
    int rc;

retry:
    kaddr = follow_table(mm, uaddr, write);
    if (IS_ERR_VALUE(kaddr))
        goto fault;

    return kaddr;
fault:
    spin_unlock(&mm->page_table_lock);
    rc = __handle_fault(uaddr, -kaddr, write);
    spin_lock(&mm->page_table_lock);
    if (!rc)
        goto retry;
    return 0;
}

size_t copy_from_user_pt(size_t n, const void __user *from, void *to)
{
    size_t rc;

    if (segment_eq(get_fs(), KERNEL_DS)) {
        memcpy(to, (void __kernel __force *) from, n);
        return 0;
    }
    rc = __user_copy_pt((unsigned long) from, to, n, 0);
    if (unlikely(rc))
        memset(to + n - rc, 0, rc);
    return rc;
}

size_t copy_to_user_pt(size_t n, void __user *to, const void *from)
{
    if (segment_eq(get_fs(), KERNEL_DS)) {
        memcpy((void __kernel __force *) to, from, n);
        return 0;
    }
    return __user_copy_pt((unsigned long) to, (void *) from, n, 1);
}

static size_t clear_user_pt(size_t n, void __user *to)
{
    long done, size, ret;

    if (segment_eq(get_fs(), KERNEL_DS)) {
        memset((void __kernel __force *) to, 0, n);
        return 0;
    }
    done = 0;
    do {
        if (n - done > PAGE_SIZE)
            size = PAGE_SIZE;
        else
            size = n - done;
        ret = __user_copy_pt((unsigned long) to + done,
                      &empty_zero_page, size, 1);
        done += size;
        if (ret)
            return ret + n - done;
    } while (done < n);
    return 0;
}

static size_t strnlen_user_pt(size_t count, const char __user *src)
{
    unsigned long uaddr = (unsigned long) src;
    struct mm_struct *mm = current->mm;
    unsigned long offset, done, len, kaddr;
    size_t len_str;

    if (segment_eq(get_fs(), KERNEL_DS))
        return strnlen((const char __kernel __force *) src, count) + 1;
    done = 0;
retry:
    spin_lock(&mm->page_table_lock);
    do {
        kaddr = follow_table(mm, uaddr, 0);
        if (IS_ERR_VALUE(kaddr))
            goto fault;

        offset = uaddr & ~PAGE_MASK;
        len = min(count - done, PAGE_SIZE - offset);
        len_str = strnlen((char *) kaddr, len);
        done += len_str;
        uaddr += len_str;
    } while ((len_str == len) && (done < count));
    spin_unlock(&mm->page_table_lock);
    return done + 1;
fault:
    spin_unlock(&mm->page_table_lock);
    if (__handle_fault(uaddr, -kaddr, 0))
        return 0;
    goto retry;
}

static size_t strncpy_from_user_pt(size_t count, const char __user *src,
                   char *dst)
{
    size_t n = strnlen_user_pt(count, src);

    if (!n)
        return -EFAULT;
    if (n > count)
        n = count;
    if (segment_eq(get_fs(), KERNEL_DS)) {
        memcpy(dst, (const char __kernel __force *) src, n);
        if (dst[n-1] == '\0')
            return n-1;
        else
            return n;
    }
    if (__user_copy_pt((unsigned long) src, dst, n, 0))
        return -EFAULT;
    if (dst[n-1] == '\0')
        return n-1;
    else
        return n;
}

static size_t copy_in_user_pt(size_t n, void __user *to,
                  const void __user *from)
{
    struct mm_struct *mm = current->mm;
    unsigned long offset_max, uaddr, done, size, error_code;
    unsigned long uaddr_from = (unsigned long) from;
    unsigned long uaddr_to = (unsigned long) to;
    unsigned long kaddr_to, kaddr_from;
    int write_user;

    if (segment_eq(get_fs(), KERNEL_DS)) {
        memcpy((void __force *) to, (void __force *) from, n);
        return 0;
    }
    done = 0;
retry:
    spin_lock(&mm->page_table_lock);
    do {
        write_user = 0;
        uaddr = uaddr_from;
        kaddr_from = follow_table(mm, uaddr_from, 0);
        error_code = kaddr_from;
        if (IS_ERR_VALUE(error_code))
            goto fault;

        write_user = 1;
        uaddr = uaddr_to;
        kaddr_to = follow_table(mm, uaddr_to, 1);
        error_code = (unsigned long) kaddr_to;
        if (IS_ERR_VALUE(error_code))
            goto fault;

        offset_max = max(uaddr_from & ~PAGE_MASK,
                 uaddr_to & ~PAGE_MASK);
        size = min(n - done, PAGE_SIZE - offset_max);

        memcpy((void *) kaddr_to, (void *) kaddr_from, size);
        done += size;
        uaddr_from += size;
        uaddr_to += size;
    } while (done < n);
    spin_unlock(&mm->page_table_lock);
    return n - done;
fault:
    spin_unlock(&mm->page_table_lock);
    if (__handle_fault(uaddr, -error_code, write_user))
        return n - done;
    goto retry;
}

#define __futex_atomic_op(insn, ret, oldval, newval, uaddr, oparg)  \
    asm volatile("0: l   %1,0(%6)\n"                \
             "1: " insn                     \
             "2: cs  %1,%2,0(%6)\n"             \
             "3: jl  1b\n"                  \
             "   lhi %0,0\n"                    \
             "4:\n"                     \
             EX_TABLE(0b,4b) EX_TABLE(2b,4b) EX_TABLE(3b,4b)    \
             : "=d" (ret), "=&d" (oldval), "=&d" (newval),  \
               "=m" (*uaddr)                    \
             : "0" (-EFAULT), "d" (oparg), "a" (uaddr),     \
               "m" (*uaddr) : "cc" );

static int __futex_atomic_op_pt(int op, u32 __user *uaddr, int oparg, int *old)
{
    int oldval = 0, newval, ret;

    switch (op) {
    case FUTEX_OP_SET:
        __futex_atomic_op("lr %2,%5\n",
                  ret, oldval, newval, uaddr, oparg);
        break;
    case FUTEX_OP_ADD:
        __futex_atomic_op("lr %2,%1\nar %2,%5\n",
                  ret, oldval, newval, uaddr, oparg);
        break;
    case FUTEX_OP_OR:
        __futex_atomic_op("lr %2,%1\nor %2,%5\n",
                  ret, oldval, newval, uaddr, oparg);
        break;
    case FUTEX_OP_ANDN:
        __futex_atomic_op("lr %2,%1\nnr %2,%5\n",
                  ret, oldval, newval, uaddr, oparg);
        break;
    case FUTEX_OP_XOR:
        __futex_atomic_op("lr %2,%1\nxr %2,%5\n",
                  ret, oldval, newval, uaddr, oparg);
        break;
    default:
        ret = -ENOSYS;
    }
    if (ret == 0)
        *old = oldval;
    return ret;
}

int futex_atomic_op_pt(int op, u32 __user *uaddr, int oparg, int *old)
{
    int ret;

    if (segment_eq(get_fs(), KERNEL_DS))
        return __futex_atomic_op_pt(op, uaddr, oparg, old);
    spin_lock(&current->mm->page_table_lock);
    uaddr = (u32 __force __user *)
        __dat_user_addr((__force unsigned long) uaddr, 1);
    if (!uaddr) {
        spin_unlock(&current->mm->page_table_lock);
        return -EFAULT;
    }
    get_page(virt_to_page(uaddr));
    spin_unlock(&current->mm->page_table_lock);
    ret = __futex_atomic_op_pt(op, uaddr, oparg, old);
    put_page(virt_to_page(uaddr));
    return ret;
}

static int __futex_atomic_cmpxchg_pt(u32 *uval, u32 __user *uaddr,
                     u32 oldval, u32 newval)
{
    int ret;

    asm volatile("0: cs   %1,%4,0(%5)\n"
             "1: la   %0,0\n"
             "2:\n"
             EX_TABLE(0b,2b) EX_TABLE(1b,2b)
             : "=d" (ret), "+d" (oldval), "=m" (*uaddr)
             : "0" (-EFAULT), "d" (newval), "a" (uaddr), "m" (*uaddr)
             : "cc", "memory" );
    *uval = oldval;
    return ret;
}

int futex_atomic_cmpxchg_pt(u32 *uval, u32 __user *uaddr,
                u32 oldval, u32 newval)
{
    int ret;

    if (segment_eq(get_fs(), KERNEL_DS))
        return __futex_atomic_cmpxchg_pt(uval, uaddr, oldval, newval);
    spin_lock(&current->mm->page_table_lock);
    uaddr = (u32 __force __user *)
        __dat_user_addr((__force unsigned long) uaddr, 1);
    if (!uaddr) {
        spin_unlock(&current->mm->page_table_lock);
        return -EFAULT;
    }
    get_page(virt_to_page(uaddr));
    spin_unlock(&current->mm->page_table_lock);
    ret = __futex_atomic_cmpxchg_pt(uval, uaddr, oldval, newval);
    put_page(virt_to_page(uaddr));
    return ret;
}

struct uaccess_ops uaccess_pt = {
    .copy_from_user     = copy_from_user_pt,
    .copy_from_user_small   = copy_from_user_pt,
    .copy_to_user       = copy_to_user_pt,
    .copy_to_user_small = copy_to_user_pt,
    .copy_in_user       = copy_in_user_pt,
    .clear_user     = clear_user_pt,
    .strnlen_user       = strnlen_user_pt,
    .strncpy_from_user  = strncpy_from_user_pt,
    .futex_atomic_op    = futex_atomic_op_pt,
    .futex_atomic_cmpxchg   = futex_atomic_cmpxchg_pt,
};