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 */
8
9#include <linux/uaccess.h>
10#include <linux/kernel.h>
11#include <linux/types.h>
12#include <linux/errno.h>
13#include <linux/gfp.h>
14#include <linux/cpu.h>
15#include <linux/uio.h>
16#include <linux/io.h>
17#include <asm/asm-extable.h>
18#include <asm/abs_lowcore.h>
19#include <asm/stacktrace.h>
20#include <asm/sections.h>
21#include <asm/maccess.h>
22#include <asm/ctlreg.h>
23
24unsigned long __bootdata_preserved(__memcpy_real_area);
25pte_t *__bootdata_preserved(memcpy_real_ptep);
26static DEFINE_MUTEX(memcpy_real_mutex);
27
28static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t size)
29{
30 unsigned long aligned, offset, count;
31 char tmp[8];
32
33 aligned = (unsigned long) dst & ~7UL;
34 offset = (unsigned long) dst & 7UL;
35 size = min(8UL - offset, size);
36 count = size - 1;
37 asm volatile(
38 " bras 1,0f\n"
39 " mvc 0(1,%4),0(%5)\n"
40 "0: mvc 0(8,%3),0(%0)\n"
41 " ex %1,0(1)\n"
42 " lg %1,0(%3)\n"
43 " lra %0,0(%0)\n"
44 " sturg %1,%0"
45 : "+&a" (aligned), "+&a" (count), "=m" (tmp)
46 : "a" (&tmp), "a" (&tmp[offset]), "a" (src)
47 : "cc", "memory", "1");
48 return size;
49}
50
51/*
52 * __s390_kernel_write - write to kernel memory bypassing DAT
53 * @dst: destination address
54 * @src: source address
55 * @size: number of bytes to copy
56 *
57 * This function writes to kernel memory bypassing DAT and possible page table
58 * write protection. It writes to the destination using the sturg instruction.
59 * Therefore we have a read-modify-write sequence: the function reads eight
60 * bytes from destination at an eight byte boundary, modifies the bytes
61 * requested and writes the result back in a loop.
62 */
63static DEFINE_SPINLOCK(s390_kernel_write_lock);
64
65notrace void *__s390_kernel_write(void *dst, const void *src, size_t size)
66{
67 void *tmp = dst;
68 unsigned long flags;
69 long copied;
70
71 spin_lock_irqsave(&s390_kernel_write_lock, flags);
72 while (size) {
73 copied = s390_kernel_write_odd(dst: tmp, src, size);
74 tmp += copied;
75 src += copied;
76 size -= copied;
77 }
78 spin_unlock_irqrestore(lock: &s390_kernel_write_lock, flags);
79
80 return dst;
81}
82
83size_t memcpy_real_iter(struct iov_iter *iter, unsigned long src, size_t count)
84{
85 size_t len, copied, res = 0;
86 unsigned long phys, offset;
87 void *chunk;
88 pte_t pte;
89
90 BUILD_BUG_ON(MEMCPY_REAL_SIZE != PAGE_SIZE);
91 while (count) {
92 phys = src & MEMCPY_REAL_MASK;
93 offset = src & ~MEMCPY_REAL_MASK;
94 chunk = (void *)(__memcpy_real_area + offset);
95 len = min(count, MEMCPY_REAL_SIZE - offset);
96 pte = mk_pte_phys(phys, PAGE_KERNEL_RO);
97
98 mutex_lock(&memcpy_real_mutex);
99 if (pte_val(pte) != pte_val(pte: *memcpy_real_ptep)) {
100 __ptep_ipte(__memcpy_real_area, memcpy_real_ptep, 0, 0, IPTE_GLOBAL);
101 set_pte(ptep: memcpy_real_ptep, pte);
102 }
103 copied = copy_to_iter(addr: chunk, bytes: len, i: iter);
104 mutex_unlock(lock: &memcpy_real_mutex);
105
106 count -= copied;
107 src += copied;
108 res += copied;
109 if (copied < len)
110 break;
111 }
112 return res;
113}
114
115int memcpy_real(void *dest, unsigned long src, size_t count)
116{
117 struct iov_iter iter;
118 struct kvec kvec;
119
120 kvec.iov_base = dest;
121 kvec.iov_len = count;
122 iov_iter_kvec(i: &iter, ITER_DEST, kvec: &kvec, nr_segs: 1, count);
123 if (memcpy_real_iter(iter: &iter, src, count) < count)
124 return -EFAULT;
125 return 0;
126}
127
128/*
129 * Find CPU that owns swapped prefix page
130 */
131static int get_swapped_owner(phys_addr_t addr)
132{
133 phys_addr_t lc;
134 int cpu;
135
136 for_each_online_cpu(cpu) {
137 lc = virt_to_phys(lowcore_ptr[cpu]);
138 if (addr > lc + sizeof(struct lowcore) - 1 || addr < lc)
139 continue;
140 return cpu;
141 }
142 return -1;
143}
144
145/*
146 * Convert a physical pointer for /dev/mem access
147 *
148 * For swapped prefix pages a new buffer is returned that contains a copy of
149 * the absolute memory. The buffer size is maximum one page large.
150 */
151void *xlate_dev_mem_ptr(phys_addr_t addr)
152{
153 void *ptr = phys_to_virt(address: addr);
154 void *bounce = ptr;
155 struct lowcore *abs_lc;
156 unsigned long size;
157 int this_cpu, cpu;
158
159 cpus_read_lock();
160 this_cpu = get_cpu();
161 if (addr >= sizeof(struct lowcore)) {
162 cpu = get_swapped_owner(addr);
163 if (cpu < 0)
164 goto out;
165 }
166 bounce = (void *)__get_free_page(GFP_ATOMIC);
167 if (!bounce)
168 goto out;
169 size = PAGE_SIZE - (addr & ~PAGE_MASK);
170 if (addr < sizeof(struct lowcore)) {
171 abs_lc = get_abs_lowcore();
172 ptr = (void *)abs_lc + addr;
173 memcpy(bounce, ptr, size);
174 put_abs_lowcore(abs_lc);
175 } else if (cpu == this_cpu) {
176 ptr = (void *)(addr - virt_to_phys(lowcore_ptr[cpu]));
177 memcpy(bounce, ptr, size);
178 } else {
179 memcpy(bounce, ptr, size);
180 }
181out:
182 put_cpu();
183 cpus_read_unlock();
184 return bounce;
185}
186
187/*
188 * Free converted buffer for /dev/mem access (if necessary)
189 */
190void unxlate_dev_mem_ptr(phys_addr_t addr, void *ptr)
191{
192 if (addr != virt_to_phys(address: ptr))
193 free_page((unsigned long)ptr);
194}
195

source code of linux/arch/s390/mm/maccess.c