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/maccess.h>
21#include <asm/ctlreg.h>
22
23unsigned long __bootdata_preserved(__memcpy_real_area);
24pte_t *__bootdata_preserved(memcpy_real_ptep);
25static DEFINE_MUTEX(memcpy_real_mutex);
26
27static 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 */
62static DEFINE_SPINLOCK(s390_kernel_write_lock);
63
64notrace 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
82size_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
114int 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 */
130static 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 */
150void *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	}
180out:
181	put_cpu();
182	cpus_read_unlock();
183	return bounce;
184}
185
186/*
187 * Free converted buffer for /dev/mem access (if necessary)
188 */
189void 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