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 
22 static int
23 pin_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 
92 static 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 
136 out:
137 	return n;
138 }
139 
140 unsigned long
141 arm_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 
161 static 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 
196 out:
197 	return n;
198 }
199 
200 unsigned 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 
228 static 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);
272 no_vmap:
273 	put_page(dst_page);
274 no_dst:
275 	put_page(src_page);
276 no_src:
277 	return ret;
278 }
279 
280 subsys_initcall(test_size_treshold);
281 
282 #endif
283