xref: /openbmc/linux/arch/s390/mm/maccess.c (revision a984f27e)
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/ctl_reg.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 	BUILD_BUG_ON(MEMCPY_REAL_SIZE != PAGE_SIZE);
90 	while (count) {
91 		phys = src & MEMCPY_REAL_MASK;
92 		offset = src & ~MEMCPY_REAL_MASK;
93 		chunk = (void *)(__memcpy_real_area + offset);
94 		len = min(count, MEMCPY_REAL_SIZE - offset);
95 		pte = mk_pte_phys(phys, PAGE_KERNEL_RO);
96 
97 		mutex_lock(&memcpy_real_mutex);
98 		if (pte_val(pte) != pte_val(*memcpy_real_ptep)) {
99 			__ptep_ipte(__memcpy_real_area, memcpy_real_ptep, 0, 0, IPTE_GLOBAL);
100 			set_pte(memcpy_real_ptep, pte);
101 		}
102 		copied = copy_to_iter(chunk, len, iter);
103 		mutex_unlock(&memcpy_real_mutex);
104 
105 		count -= copied;
106 		src += copied;
107 		res += copied;
108 		if (copied < len)
109 			break;
110 	}
111 	return res;
112 }
113 
memcpy_real(void * dest,unsigned long src,size_t count)114 int memcpy_real(void *dest, unsigned long src, size_t count)
115 {
116 	struct iov_iter iter;
117 	struct kvec kvec;
118 
119 	kvec.iov_base = dest;
120 	kvec.iov_len = count;
121 	iov_iter_kvec(&iter, ITER_DEST, &kvec, 1, count);
122 	if (memcpy_real_iter(&iter, src, count) < count)
123 		return -EFAULT;
124 	return 0;
125 }
126 
127 /*
128  * Find CPU that owns swapped prefix page
129  */
get_swapped_owner(phys_addr_t addr)130 static int get_swapped_owner(phys_addr_t addr)
131 {
132 	phys_addr_t lc;
133 	int cpu;
134 
135 	for_each_online_cpu(cpu) {
136 		lc = virt_to_phys(lowcore_ptr[cpu]);
137 		if (addr > lc + sizeof(struct lowcore) - 1 || addr < lc)
138 			continue;
139 		return cpu;
140 	}
141 	return -1;
142 }
143 
144 /*
145  * Convert a physical pointer for /dev/mem access
146  *
147  * For swapped prefix pages a new buffer is returned that contains a copy of
148  * the absolute memory. The buffer size is maximum one page large.
149  */
xlate_dev_mem_ptr(phys_addr_t addr)150 void *xlate_dev_mem_ptr(phys_addr_t addr)
151 {
152 	void *ptr = phys_to_virt(addr);
153 	void *bounce = ptr;
154 	struct lowcore *abs_lc;
155 	unsigned long size;
156 	int this_cpu, cpu;
157 
158 	cpus_read_lock();
159 	this_cpu = get_cpu();
160 	if (addr >= sizeof(struct lowcore)) {
161 		cpu = get_swapped_owner(addr);
162 		if (cpu < 0)
163 			goto out;
164 	}
165 	bounce = (void *)__get_free_page(GFP_ATOMIC);
166 	if (!bounce)
167 		goto out;
168 	size = PAGE_SIZE - (addr & ~PAGE_MASK);
169 	if (addr < sizeof(struct lowcore)) {
170 		abs_lc = get_abs_lowcore();
171 		ptr = (void *)abs_lc + addr;
172 		memcpy(bounce, ptr, size);
173 		put_abs_lowcore(abs_lc);
174 	} else if (cpu == this_cpu) {
175 		ptr = (void *)(addr - virt_to_phys(lowcore_ptr[cpu]));
176 		memcpy(bounce, ptr, size);
177 	} else {
178 		memcpy(bounce, ptr, size);
179 	}
180 out:
181 	put_cpu();
182 	cpus_read_unlock();
183 	return bounce;
184 }
185 
186 /*
187  * Free converted buffer for /dev/mem access (if necessary)
188  */
unxlate_dev_mem_ptr(phys_addr_t addr,void * ptr)189 void unxlate_dev_mem_ptr(phys_addr_t addr, void *ptr)
190 {
191 	if (addr != virt_to_phys(ptr))
192 		free_page((unsigned long)ptr);
193 }
194