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 */
  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(tmp, src, size);
 74		tmp += copied;
 75		src += copied;
 76		size -= copied;
 77	}
 78	spin_unlock_irqrestore(&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(*memcpy_real_ptep)) {
100			__ptep_ipte(__memcpy_real_area, memcpy_real_ptep, 0, 0, IPTE_GLOBAL);
101			set_pte(memcpy_real_ptep, pte);
102		}
103		copied = copy_to_iter(chunk, len, iter);
104		mutex_unlock(&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(&iter, ITER_DEST, &kvec, 1, count);
123	if (memcpy_real_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(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(ptr))
193		free_page((unsigned long)ptr);
194}