1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 *  linux/arch/arm/lib/uaccess_with_memcpy.c
4 *
5 *  Written by: Lennert Buytenhek and Nicolas Pitre
6 *  Copyright (C) 2009 Marvell Semiconductor
7 */
8
9#include <linux/kernel.h>
10#include <linux/ctype.h>
11#include <linux/uaccess.h>
12#include <linux/rwsem.h>
13#include <linux/mm.h>
14#include <linux/sched.h>
15#include <linux/hardirq.h> /* for in_atomic() */
16#include <linux/gfp.h>
17#include <linux/highmem.h>
18#include <linux/hugetlb.h>
19#include <asm/current.h>
20#include <asm/page.h>
21
22static int
23pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
24{
25	unsigned long addr = (unsigned long)_addr;
26	pgd_t *pgd;
27	p4d_t *p4d;
28	pmd_t *pmd;
29	pte_t *pte;
30	pud_t *pud;
31	spinlock_t *ptl;
32
33	pgd = pgd_offset(current->mm, addr);
34	if (unlikely(pgd_none(*pgd) || pgd_bad(*pgd)))
35		return 0;
36
37	p4d = p4d_offset(pgd, addr);
38	if (unlikely(p4d_none(*p4d) || p4d_bad(*p4d)))
39		return 0;
40
41	pud = pud_offset(p4d, addr);
42	if (unlikely(pud_none(*pud) || pud_bad(*pud)))
43		return 0;
44
45	pmd = pmd_offset(pud, addr);
46	if (unlikely(pmd_none(*pmd)))
47		return 0;
48
49	/*
50	 * A pmd can be bad if it refers to a HugeTLB or THP page.
51	 *
52	 * Both THP and HugeTLB pages have the same pmd layout
53	 * and should not be manipulated by the pte functions.
54	 *
55	 * Lock the page table for the destination and check
56	 * to see that it's still huge and whether or not we will
57	 * need to fault on write.
58	 */
59	if (unlikely(pmd_thp_or_huge(*pmd))) {
60		ptl = &current->mm->page_table_lock;
61		spin_lock(ptl);
62		if (unlikely(!pmd_thp_or_huge(*pmd)
63			|| pmd_hugewillfault(*pmd))) {
64			spin_unlock(ptl);
65			return 0;
66		}
67
68		*ptep = NULL;
69		*ptlp = ptl;
70		return 1;
71	}
72
73	if (unlikely(pmd_bad(*pmd)))
74		return 0;
75
76	pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
77	if (unlikely(!pte))
78		return 0;
79
80	if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
81	    !pte_write(*pte) || !pte_dirty(*pte))) {
82		pte_unmap_unlock(pte, ptl);
83		return 0;
84	}
85
86	*ptep = pte;
87	*ptlp = ptl;
88
89	return 1;
90}
91
92static unsigned long noinline
93__copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
94{
95	unsigned long ua_flags;
96	int atomic;
97
98	/* the mmap semaphore is taken only if not in an atomic context */
99	atomic = faulthandler_disabled();
100
101	if (!atomic)
102		mmap_read_lock(current->mm);
103	while (n) {
104		pte_t *pte;
105		spinlock_t *ptl;
106		int tocopy;
107
108		while (!pin_page_for_write(to, &pte, &ptl)) {
109			if (!atomic)
110				mmap_read_unlock(current->mm);
111			if (__put_user(0, (char __user *)to))
112				goto out;
113			if (!atomic)
114				mmap_read_lock(current->mm);
115		}
116
117		tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
118		if (tocopy > n)
119			tocopy = n;
120
121		ua_flags = uaccess_save_and_enable();
122		__memcpy((void *)to, from, tocopy);
123		uaccess_restore(ua_flags);
124		to += tocopy;
125		from += tocopy;
126		n -= tocopy;
127
128		if (pte)
129			pte_unmap_unlock(pte, ptl);
130		else
131			spin_unlock(ptl);
132	}
133	if (!atomic)
134		mmap_read_unlock(current->mm);
135
136out:
137	return n;
138}
139
140unsigned long
141arm_copy_to_user(void __user *to, const void *from, unsigned long n)
142{
143	/*
144	 * This test is stubbed out of the main function above to keep
145	 * the overhead for small copies low by avoiding a large
146	 * register dump on the stack just to reload them right away.
147	 * With frame pointer disabled, tail call optimization kicks in
148	 * as well making this test almost invisible.
149	 */
150	if (n < 64) {
151		unsigned long ua_flags = uaccess_save_and_enable();
152		n = __copy_to_user_std(to, from, n);
153		uaccess_restore(ua_flags);
154	} else {
155		n = __copy_to_user_memcpy(uaccess_mask_range_ptr(to, n),
156					  from, n);
157	}
158	return n;
159}
160
161static unsigned long noinline
162__clear_user_memset(void __user *addr, unsigned long n)
163{
164	unsigned long ua_flags;
165
166	mmap_read_lock(current->mm);
167	while (n) {
168		pte_t *pte;
169		spinlock_t *ptl;
170		int tocopy;
171
172		while (!pin_page_for_write(addr, &pte, &ptl)) {
173			mmap_read_unlock(current->mm);
174			if (__put_user(0, (char __user *)addr))
175				goto out;
176			mmap_read_lock(current->mm);
177		}
178
179		tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
180		if (tocopy > n)
181			tocopy = n;
182
183		ua_flags = uaccess_save_and_enable();
184		__memset((void *)addr, 0, tocopy);
185		uaccess_restore(ua_flags);
186		addr += tocopy;
187		n -= tocopy;
188
189		if (pte)
190			pte_unmap_unlock(pte, ptl);
191		else
192			spin_unlock(ptl);
193	}
194	mmap_read_unlock(current->mm);
195
196out:
197	return n;
198}
199
200unsigned long arm_clear_user(void __user *addr, unsigned long n)
201{
202	/* See rational for this in __copy_to_user() above. */
203	if (n < 64) {
204		unsigned long ua_flags = uaccess_save_and_enable();
205		n = __clear_user_std(addr, n);
206		uaccess_restore(ua_flags);
207	} else {
208		n = __clear_user_memset(addr, n);
209	}
210	return n;
211}
212
213#if 0
214
215/*
216 * This code is disabled by default, but kept around in case the chosen
217 * thresholds need to be revalidated.  Some overhead (small but still)
218 * would be implied by a runtime determined variable threshold, and
219 * so far the measurement on concerned targets didn't show a worthwhile
220 * variation.
221 *
222 * Note that a fairly precise sched_clock() implementation is needed
223 * for results to make some sense.
224 */
225
226#include <linux/vmalloc.h>
227
228static int __init test_size_treshold(void)
229{
230	struct page *src_page, *dst_page;
231	void *user_ptr, *kernel_ptr;
232	unsigned long long t0, t1, t2;
233	int size, ret;
234
235	ret = -ENOMEM;
236	src_page = alloc_page(GFP_KERNEL);
237	if (!src_page)
238		goto no_src;
239	dst_page = alloc_page(GFP_KERNEL);
240	if (!dst_page)
241		goto no_dst;
242	kernel_ptr = page_address(src_page);
243	user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__PAGE_COPY));
244	if (!user_ptr)
245		goto no_vmap;
246
247	/* warm up the src page dcache */
248	ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
249
250	for (size = PAGE_SIZE; size >= 4; size /= 2) {
251		t0 = sched_clock();
252		ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
253		t1 = sched_clock();
254		ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
255		t2 = sched_clock();
256		printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
257	}
258
259	for (size = PAGE_SIZE; size >= 4; size /= 2) {
260		t0 = sched_clock();
261		ret |= __clear_user_memset(user_ptr, size);
262		t1 = sched_clock();
263		ret |= __clear_user_std(user_ptr, size);
264		t2 = sched_clock();
265		printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
266	}
267
268	if (ret)
269		ret = -EFAULT;
270
271	vunmap(user_ptr);
272no_vmap:
273	put_page(dst_page);
274no_dst:
275	put_page(src_page);
276no_src:
277	return ret;
278}
279
280subsys_initcall(test_size_treshold);
281
282#endif
283