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_present(*pte) || !pte_young(*pte) ||
78 	    !pte_write(*pte) || !pte_dirty(*pte))) {
79 		pte_unmap_unlock(pte, ptl);
80 		return 0;
81 	}
82 
83 	*ptep = pte;
84 	*ptlp = ptl;
85 
86 	return 1;
87 }
88 
89 static unsigned long noinline
90 __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
91 {
92 	unsigned long ua_flags;
93 	int atomic;
94 
95 	/* the mmap semaphore is taken only if not in an atomic context */
96 	atomic = faulthandler_disabled();
97 
98 	if (!atomic)
99 		mmap_read_lock(current->mm);
100 	while (n) {
101 		pte_t *pte;
102 		spinlock_t *ptl;
103 		int tocopy;
104 
105 		while (!pin_page_for_write(to, &pte, &ptl)) {
106 			if (!atomic)
107 				mmap_read_unlock(current->mm);
108 			if (__put_user(0, (char __user *)to))
109 				goto out;
110 			if (!atomic)
111 				mmap_read_lock(current->mm);
112 		}
113 
114 		tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
115 		if (tocopy > n)
116 			tocopy = n;
117 
118 		ua_flags = uaccess_save_and_enable();
119 		memcpy((void *)to, from, tocopy);
120 		uaccess_restore(ua_flags);
121 		to += tocopy;
122 		from += tocopy;
123 		n -= tocopy;
124 
125 		if (pte)
126 			pte_unmap_unlock(pte, ptl);
127 		else
128 			spin_unlock(ptl);
129 	}
130 	if (!atomic)
131 		mmap_read_unlock(current->mm);
132 
133 out:
134 	return n;
135 }
136 
137 unsigned long
138 arm_copy_to_user(void __user *to, const void *from, unsigned long n)
139 {
140 	/*
141 	 * This test is stubbed out of the main function above to keep
142 	 * the overhead for small copies low by avoiding a large
143 	 * register dump on the stack just to reload them right away.
144 	 * With frame pointer disabled, tail call optimization kicks in
145 	 * as well making this test almost invisible.
146 	 */
147 	if (n < 64) {
148 		unsigned long ua_flags = uaccess_save_and_enable();
149 		n = __copy_to_user_std(to, from, n);
150 		uaccess_restore(ua_flags);
151 	} else {
152 		n = __copy_to_user_memcpy(uaccess_mask_range_ptr(to, n),
153 					  from, n);
154 	}
155 	return n;
156 }
157 
158 static unsigned long noinline
159 __clear_user_memset(void __user *addr, unsigned long n)
160 {
161 	unsigned long ua_flags;
162 
163 	mmap_read_lock(current->mm);
164 	while (n) {
165 		pte_t *pte;
166 		spinlock_t *ptl;
167 		int tocopy;
168 
169 		while (!pin_page_for_write(addr, &pte, &ptl)) {
170 			mmap_read_unlock(current->mm);
171 			if (__put_user(0, (char __user *)addr))
172 				goto out;
173 			mmap_read_lock(current->mm);
174 		}
175 
176 		tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
177 		if (tocopy > n)
178 			tocopy = n;
179 
180 		ua_flags = uaccess_save_and_enable();
181 		memset((void *)addr, 0, tocopy);
182 		uaccess_restore(ua_flags);
183 		addr += tocopy;
184 		n -= tocopy;
185 
186 		if (pte)
187 			pte_unmap_unlock(pte, ptl);
188 		else
189 			spin_unlock(ptl);
190 	}
191 	mmap_read_unlock(current->mm);
192 
193 out:
194 	return n;
195 }
196 
197 unsigned long arm_clear_user(void __user *addr, unsigned long n)
198 {
199 	/* See rational for this in __copy_to_user() above. */
200 	if (n < 64) {
201 		unsigned long ua_flags = uaccess_save_and_enable();
202 		n = __clear_user_std(addr, n);
203 		uaccess_restore(ua_flags);
204 	} else {
205 		n = __clear_user_memset(addr, n);
206 	}
207 	return n;
208 }
209 
210 #if 0
211 
212 /*
213  * This code is disabled by default, but kept around in case the chosen
214  * thresholds need to be revalidated.  Some overhead (small but still)
215  * would be implied by a runtime determined variable threshold, and
216  * so far the measurement on concerned targets didn't show a worthwhile
217  * variation.
218  *
219  * Note that a fairly precise sched_clock() implementation is needed
220  * for results to make some sense.
221  */
222 
223 #include <linux/vmalloc.h>
224 
225 static int __init test_size_treshold(void)
226 {
227 	struct page *src_page, *dst_page;
228 	void *user_ptr, *kernel_ptr;
229 	unsigned long long t0, t1, t2;
230 	int size, ret;
231 
232 	ret = -ENOMEM;
233 	src_page = alloc_page(GFP_KERNEL);
234 	if (!src_page)
235 		goto no_src;
236 	dst_page = alloc_page(GFP_KERNEL);
237 	if (!dst_page)
238 		goto no_dst;
239 	kernel_ptr = page_address(src_page);
240 	user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
241 	if (!user_ptr)
242 		goto no_vmap;
243 
244 	/* warm up the src page dcache */
245 	ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
246 
247 	for (size = PAGE_SIZE; size >= 4; size /= 2) {
248 		t0 = sched_clock();
249 		ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
250 		t1 = sched_clock();
251 		ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
252 		t2 = sched_clock();
253 		printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
254 	}
255 
256 	for (size = PAGE_SIZE; size >= 4; size /= 2) {
257 		t0 = sched_clock();
258 		ret |= __clear_user_memset(user_ptr, size);
259 		t1 = sched_clock();
260 		ret |= __clear_user_std(user_ptr, size);
261 		t2 = sched_clock();
262 		printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
263 	}
264 
265 	if (ret)
266 		ret = -EFAULT;
267 
268 	vunmap(user_ptr);
269 no_vmap:
270 	put_page(dst_page);
271 no_dst:
272 	put_page(src_page);
273 no_src:
274 	return ret;
275 }
276 
277 subsys_initcall(test_size_treshold);
278 
279 #endif
280