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 <asm/asm-extable.h>
17 #include <asm/ctl_reg.h>
18 #include <asm/io.h>
19 #include <asm/abs_lowcore.h>
20 #include <asm/stacktrace.h>
21 #include <asm/maccess.h>
22
23 unsigned long __bootdata_preserved(__memcpy_real_area);
24 pte_t *__bootdata_preserved(memcpy_real_ptep);
25 static DEFINE_MUTEX(memcpy_real_mutex);
26
s390_kernel_write_odd(void * dst,const void * src,size_t size)27 static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t size)
28 {
29 unsigned long aligned, offset, count;
30 char tmp[8];
31
32 aligned = (unsigned long) dst & ~7UL;
33 offset = (unsigned long) dst & 7UL;
34 size = min(8UL - offset, size);
35 count = size - 1;
36 asm volatile(
37 " bras 1,0f\n"
38 " mvc 0(1,%4),0(%5)\n"
39 "0: mvc 0(8,%3),0(%0)\n"
40 " ex %1,0(1)\n"
41 " lg %1,0(%3)\n"
42 " lra %0,0(%0)\n"
43 " sturg %1,%0\n"
44 : "+&a" (aligned), "+&a" (count), "=m" (tmp)
45 : "a" (&tmp), "a" (&tmp[offset]), "a" (src)
46 : "cc", "memory", "1");
47 return size;
48 }
49
50 /*
51 * s390_kernel_write - write to kernel memory bypassing DAT
52 * @dst: destination address
53 * @src: source address
54 * @size: number of bytes to copy
55 *
56 * This function writes to kernel memory bypassing DAT and possible page table
57 * write protection. It writes to the destination using the sturg instruction.
58 * Therefore we have a read-modify-write sequence: the function reads eight
59 * bytes from destination at an eight byte boundary, modifies the bytes
60 * requested and writes the result back in a loop.
61 */
62 static DEFINE_SPINLOCK(s390_kernel_write_lock);
63
s390_kernel_write(void * dst,const void * src,size_t size)64 notrace void *s390_kernel_write(void *dst, const void *src, size_t size)
65 {
66 void *tmp = dst;
67 unsigned long flags;
68 long copied;
69
70 spin_lock_irqsave(&s390_kernel_write_lock, flags);
71 while (size) {
72 copied = s390_kernel_write_odd(tmp, src, size);
73 tmp += copied;
74 src += copied;
75 size -= copied;
76 }
77 spin_unlock_irqrestore(&s390_kernel_write_lock, flags);
78
79 return dst;
80 }
81
memcpy_real_iter(struct iov_iter * iter,unsigned long src,size_t count)82 size_t memcpy_real_iter(struct iov_iter *iter, unsigned long src, size_t count)
83 {
84 size_t len, copied, res = 0;
85 unsigned long phys, offset;
86 void *chunk;
87 pte_t pte;
88
89 while (count) {
90 phys = src & PAGE_MASK;
91 offset = src & ~PAGE_MASK;
92 chunk = (void *)(__memcpy_real_area + offset);
93 len = min(count, PAGE_SIZE - offset);
94 pte = mk_pte_phys(phys, PAGE_KERNEL_RO);
95
96 mutex_lock(&memcpy_real_mutex);
97 if (pte_val(pte) != pte_val(*memcpy_real_ptep)) {
98 __ptep_ipte(__memcpy_real_area, memcpy_real_ptep, 0, 0, IPTE_GLOBAL);
99 set_pte(memcpy_real_ptep, pte);
100 }
101 copied = copy_to_iter(chunk, len, iter);
102 mutex_unlock(&memcpy_real_mutex);
103
104 count -= copied;
105 src += copied;
106 res += copied;
107 if (copied < len)
108 break;
109 }
110 return res;
111 }
112
memcpy_real(void * dest,unsigned long src,size_t count)113 int memcpy_real(void *dest, unsigned long src, size_t count)
114 {
115 struct iov_iter iter;
116 struct kvec kvec;
117
118 kvec.iov_base = dest;
119 kvec.iov_len = count;
120 iov_iter_kvec(&iter, ITER_DEST, &kvec, 1, count);
121 if (memcpy_real_iter(&iter, src, count) < count)
122 return -EFAULT;
123 return 0;
124 }
125
126 /*
127 * Find CPU that owns swapped prefix page
128 */
get_swapped_owner(phys_addr_t addr)129 static int get_swapped_owner(phys_addr_t addr)
130 {
131 phys_addr_t lc;
132 int cpu;
133
134 for_each_online_cpu(cpu) {
135 lc = virt_to_phys(lowcore_ptr[cpu]);
136 if (addr > lc + sizeof(struct lowcore) - 1 || addr < lc)
137 continue;
138 return cpu;
139 }
140 return -1;
141 }
142
143 /*
144 * Convert a physical pointer for /dev/mem access
145 *
146 * For swapped prefix pages a new buffer is returned that contains a copy of
147 * the absolute memory. The buffer size is maximum one page large.
148 */
xlate_dev_mem_ptr(phys_addr_t addr)149 void *xlate_dev_mem_ptr(phys_addr_t addr)
150 {
151 void *ptr = phys_to_virt(addr);
152 void *bounce = ptr;
153 struct lowcore *abs_lc;
154 unsigned long size;
155 int this_cpu, cpu;
156
157 cpus_read_lock();
158 this_cpu = get_cpu();
159 if (addr >= sizeof(struct lowcore)) {
160 cpu = get_swapped_owner(addr);
161 if (cpu < 0)
162 goto out;
163 }
164 bounce = (void *)__get_free_page(GFP_ATOMIC);
165 if (!bounce)
166 goto out;
167 size = PAGE_SIZE - (addr & ~PAGE_MASK);
168 if (addr < sizeof(struct lowcore)) {
169 abs_lc = get_abs_lowcore();
170 ptr = (void *)abs_lc + addr;
171 memcpy(bounce, ptr, size);
172 put_abs_lowcore(abs_lc);
173 } else if (cpu == this_cpu) {
174 ptr = (void *)(addr - virt_to_phys(lowcore_ptr[cpu]));
175 memcpy(bounce, ptr, size);
176 } else {
177 memcpy(bounce, ptr, size);
178 }
179 out:
180 put_cpu();
181 cpus_read_unlock();
182 return bounce;
183 }
184
185 /*
186 * Free converted buffer for /dev/mem access (if necessary)
187 */
unxlate_dev_mem_ptr(phys_addr_t addr,void * ptr)188 void unxlate_dev_mem_ptr(phys_addr_t addr, void *ptr)
189 {
190 if (addr != virt_to_phys(ptr))
191 free_page((unsigned long)ptr);
192 }
193