arch/s390/mm/maccess.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Access kernel memory without faulting -- s390 specific implementation.
   4  *
   5  * Copyright IBM Corp. 2009, 2015
   6  *
   7  *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
   8  *
   9  */
  10
  11 #include <linux/uaccess.h>
  12 #include <linux/kernel.h>
  13 #include <linux/types.h>
  14 #include <linux/errno.h>
  15 #include <linux/gfp.h>
  16 #include <linux/cpu.h>
  17 #include <asm/ctl_reg.h>
  18 #include <asm/io.h>
  19 #include <asm/stacktrace.h>
  20
  21 static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t size)
  22 {
  23         unsigned long aligned, offset, count;
  24         char tmp[8];
  25
  26         aligned = (unsigned long) dst & ~7UL;
  27         offset = (unsigned long) dst & 7UL;
  28         size = min(8UL - offset, size);
  29         count = size - 1;
  30         asm volatile(
  31                 "       bras    1,0f\n"
  32                 "       mvc     0(1,%4),0(%5)\n"
  33                 "0:     mvc     0(8,%3),0(%0)\n"
  34                 "       ex      %1,0(1)\n"
  35                 "       lg      %1,0(%3)\n"
  36                 "       lra     %0,0(%0)\n"
  37                 "       sturg   %1,%0\n"
  38                 : "+&a" (aligned), "+&a" (count), "=m" (tmp)
  39                 : "a" (&tmp), "a" (&tmp[offset]), "a" (src)
  40                 : "cc", "memory", "1");
  41         return size;
  42 }
  43
  44 /*
  45  * s390_kernel_write - write to kernel memory bypassing DAT
  46  * @dst: destination address
  47  * @src: source address
  48  * @size: number of bytes to copy
  49  *
  50  * This function writes to kernel memory bypassing DAT and possible page table
  51  * write protection. It writes to the destination using the sturg instruction.
  52  * Therefore we have a read-modify-write sequence: the function reads eight
  53  * bytes from destination at an eight byte boundary, modifies the bytes
  54  * requested and writes the result back in a loop.
  55  */
  56 static DEFINE_SPINLOCK(s390_kernel_write_lock);
  57
  58 notrace void *s390_kernel_write(void *dst, const void *src, size_t size)
  59 {
  60         void *tmp = dst;
  61         unsigned long flags;
  62         long copied;
  63
  64         spin_lock_irqsave(&s390_kernel_write_lock, flags);
  65         if (!(flags & PSW_MASK_DAT)) {
  66                 memcpy(dst, src, size);
  67         } else {
  68                 while (size) {
  69                         copied = s390_kernel_write_odd(tmp, src, size);
  70                         tmp += copied;
  71                         src += copied;
  72                         size -= copied;
  73                 }
  74         }
  75         spin_unlock_irqrestore(&s390_kernel_write_lock, flags);
  76
  77         return dst;
  78 }
  79
  80 static int __no_sanitize_address __memcpy_real(void *dest, void *src, size_t count)
  81 {
  82         register unsigned long _dest asm("2") = (unsigned long) dest;
  83         register unsigned long _len1 asm("3") = (unsigned long) count;
  84         register unsigned long _src  asm("4") = (unsigned long) src;
  85         register unsigned long _len2 asm("5") = (unsigned long) count;
  86         int rc = -EFAULT;
  87
  88         asm volatile (
  89                 "0:     mvcle   %1,%2,0x0\n"
  90                 "1:     jo      0b\n"
  91                 "       lhi     %0,0x0\n"
  92                 "2:\n"
  93                 EX_TABLE(1b,2b)
  94                 : "+d" (rc), "+d" (_dest), "+d" (_src), "+d" (_len1),
  95                   "+d" (_len2), "=m" (*((long *) dest))
  96                 : "m" (*((long *) src))
  97                 : "cc", "memory");
  98         return rc;
  99 }
 100
 101 static unsigned long __no_sanitize_address _memcpy_real(unsigned long dest,
 102                                                         unsigned long src,
 103                                                         unsigned long count)
 104 {
 105         int irqs_disabled, rc;
 106         unsigned long flags;
 107
 108         if (!count)
 109                 return 0;
 110         flags = arch_local_irq_save();
 111         irqs_disabled = arch_irqs_disabled_flags(flags);
 112         if (!irqs_disabled)
 113                 trace_hardirqs_off();
 114         __arch_local_irq_stnsm(0xf8); // disable DAT
 115         rc = __memcpy_real((void *) dest, (void *) src, (size_t) count);
 116         if (flags & PSW_MASK_DAT)
 117                 __arch_local_irq_stosm(0x04); // enable DAT
 118         if (!irqs_disabled)
 119                 trace_hardirqs_on();
 120         __arch_local_irq_ssm(flags);
 121         return rc;
 122 }
 123
 124 /*
 125  * Copy memory in real mode (kernel to kernel)
 126  */
 127 int memcpy_real(void *dest, void *src, size_t count)
 128 {
 129         int rc;
 130
 131         if (S390_lowcore.nodat_stack != 0) {
 132                 preempt_disable();
 133                 rc = CALL_ON_STACK(_memcpy_real, S390_lowcore.nodat_stack, 3,
 134                                    dest, src, count);
 135                 preempt_enable();
 136                 return rc;
 137         }
 138         /*
 139          * This is a really early memcpy_real call, the stacks are
 140          * not set up yet. Just call _memcpy_real on the early boot
 141          * stack
 142          */
 143         return _memcpy_real((unsigned long) dest,(unsigned long) src,
 144                             (unsigned long) count);
 145 }
 146
 147 /*
 148  * Copy memory in absolute mode (kernel to kernel)
 149  */
 150 void memcpy_absolute(void *dest, void *src, size_t count)
 151 {
 152         unsigned long cr0, flags, prefix;
 153
 154         flags = arch_local_irq_save();
 155         __ctl_store(cr0, 0, 0);
 156         __ctl_clear_bit(0, 28); /* disable lowcore protection */
 157         prefix = store_prefix();
 158         if (prefix) {
 159                 local_mcck_disable();
 160                 set_prefix(0);
 161                 memcpy(dest, src, count);
 162                 set_prefix(prefix);
 163                 local_mcck_enable();
 164         } else {
 165                 memcpy(dest, src, count);
 166         }
 167         __ctl_load(cr0, 0, 0);
 168         arch_local_irq_restore(flags);
 169 }
 170
 171 /*
 172  * Copy memory from kernel (real) to user (virtual)
 173  */
 174 int copy_to_user_real(void __user *dest, void *src, unsigned long count)
 175 {
 176         int offs = 0, size, rc;
 177         char *buf;
 178
 179         buf = (char *) __get_free_page(GFP_KERNEL);
 180         if (!buf)
 181                 return -ENOMEM;
 182         rc = -EFAULT;
 183         while (offs < count) {
 184                 size = min(PAGE_SIZE, count - offs);
 185                 if (memcpy_real(buf, src + offs, size))
 186                         goto out;
 187                 if (copy_to_user(dest + offs, buf, size))
 188                         goto out;
 189                 offs += size;
 190         }
 191         rc = 0;
 192 out:
 193         free_page((unsigned long) buf);
 194         return rc;
 195 }
 196
 197 /*
 198  * Check if physical address is within prefix or zero page
 199  */
 200 static int is_swapped(unsigned long addr)
 201 {
 202         unsigned long lc;
 203         int cpu;
 204
 205         if (addr < sizeof(struct lowcore))
 206                 return 1;
 207         for_each_online_cpu(cpu) {
 208                 lc = (unsigned long) lowcore_ptr[cpu];
 209                 if (addr > lc + sizeof(struct lowcore) - 1 || addr < lc)
 210                         continue;
 211                 return 1;
 212         }
 213         return 0;
 214 }
 215
 216 /*
 217  * Convert a physical pointer for /dev/mem access
 218  *
 219  * For swapped prefix pages a new buffer is returned that contains a copy of
 220  * the absolute memory. The buffer size is maximum one page large.
 221  */
 222 void *xlate_dev_mem_ptr(phys_addr_t addr)
 223 {
 224         void *bounce = (void *) addr;
 225         unsigned long size;
 226
 227         get_online_cpus();
 228         preempt_disable();
 229         if (is_swapped(addr)) {
 230                 size = PAGE_SIZE - (addr & ~PAGE_MASK);
 231                 bounce = (void *) __get_free_page(GFP_ATOMIC);
 232                 if (bounce)
 233                         memcpy_absolute(bounce, (void *) addr, size);
 234         }
 235         preempt_enable();
 236         put_online_cpus();
 237         return bounce;
 238 }
 239
 240 /*
 241  * Free converted buffer for /dev/mem access (if necessary)
 242  */
 243 void unxlate_dev_mem_ptr(phys_addr_t addr, void *buf)
 244 {
 245         if ((void *) addr != buf)
 246                 free_page((unsigned long) buf);
 247 }