scatterwalk.h

  1/* SPDX-License-Identifier: GPL-2.0-or-later */
  2/*
  3 * Cryptographic scatter and gather helpers.
  4 *
  5 * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
  6 * Copyright (c) 2002 Adam J. Richter <adam@yggdrasil.com>
  7 * Copyright (c) 2004 Jean-Luc Cooke <jlcooke@certainkey.com>
  8 * Copyright (c) 2007 Herbert Xu <herbert@gondor.apana.org.au>
  9 */
 10
 11#ifndef _CRYPTO_SCATTERWALK_H
 12#define _CRYPTO_SCATTERWALK_H
 13
 14#include <crypto/algapi.h>
 15
 16#include <linux/highmem.h>
 17#include <linux/mm.h>
 18#include <linux/scatterlist.h>
 19
 20static inline void scatterwalk_crypto_chain(struct scatterlist *head,
 21					    struct scatterlist *sg, int num)
 22{
 23	if (sg)
 24		sg_chain(head, num, sg);
 25	else
 26		sg_mark_end(head);
 27}
 28
 29static inline void scatterwalk_start(struct scatter_walk *walk,
 30				     struct scatterlist *sg)
 31{
 32	walk->sg = sg;
 33	walk->offset = sg->offset;
 34}
 35
 36/*
 37 * This is equivalent to scatterwalk_start(walk, sg) followed by
 38 * scatterwalk_skip(walk, pos).
 39 */
 40static inline void scatterwalk_start_at_pos(struct scatter_walk *walk,
 41					    struct scatterlist *sg,
 42					    unsigned int pos)
 43{
 44	while (pos > sg->length) {
 45		pos -= sg->length;
 46		sg = sg_next(sg);
 47	}
 48	walk->sg = sg;
 49	walk->offset = sg->offset + pos;
 50}
 51
 52static inline unsigned int scatterwalk_clamp(struct scatter_walk *walk,
 53					     unsigned int nbytes)
 54{
 55	unsigned int len_this_sg;
 56	unsigned int limit;
 57
 58	if (walk->offset >= walk->sg->offset + walk->sg->length)
 59		scatterwalk_start(walk, sg_next(walk->sg));
 60	len_this_sg = walk->sg->offset + walk->sg->length - walk->offset;
 61
 62	/*
 63	 * HIGHMEM case: the page may have to be mapped into memory.  To avoid
 64	 * the complexity of having to map multiple pages at once per sg entry,
 65	 * clamp the returned length to not cross a page boundary.
 66	 *
 67	 * !HIGHMEM case: no mapping is needed; all pages of the sg entry are
 68	 * already mapped contiguously in the kernel's direct map.  For improved
 69	 * performance, allow the walker to return data segments that cross a
 70	 * page boundary.  Do still cap the length to PAGE_SIZE, since some
 71	 * users rely on that to avoid disabling preemption for too long when
 72	 * using SIMD.  It's also needed for when skcipher_walk uses a bounce
 73	 * page due to the data not being aligned to the algorithm's alignmask.
 74	 */
 75	if (IS_ENABLED(CONFIG_HIGHMEM))
 76		limit = PAGE_SIZE - offset_in_page(walk->offset);
 77	else
 78		limit = PAGE_SIZE;
 79
 80	return min3(nbytes, len_this_sg, limit);
 81}
 82
 83/*
 84 * Create a scatterlist that represents the remaining data in a walk.  Uses
 85 * chaining to reference the original scatterlist, so this uses at most two
 86 * entries in @sg_out regardless of the number of entries in the original list.
 87 * Assumes that sg_init_table() was already done.
 88 */
 89static inline void scatterwalk_get_sglist(struct scatter_walk *walk,
 90					  struct scatterlist sg_out[2])
 91{
 92	if (walk->offset >= walk->sg->offset + walk->sg->length)
 93		scatterwalk_start(walk, sg_next(walk->sg));
 94	sg_set_page(sg_out, sg_page(walk->sg),
 95		    walk->sg->offset + walk->sg->length - walk->offset,
 96		    walk->offset);
 97	scatterwalk_crypto_chain(sg_out, sg_next(walk->sg), 2);
 98}
 99
100static inline void scatterwalk_map(struct scatter_walk *walk)
101{
102	struct page *base_page = sg_page(walk->sg);
103	unsigned int offset = walk->offset;
104	void *addr;
105
106	if (IS_ENABLED(CONFIG_HIGHMEM)) {
107		struct page *page;
108
109		page = base_page + (offset >> PAGE_SHIFT);
110		offset = offset_in_page(offset);
111		addr = kmap_local_page(page) + offset;
112	} else {
113		/*
114		 * When !HIGHMEM we allow the walker to return segments that
115		 * span a page boundary; see scatterwalk_clamp().  To make it
116		 * clear that in this case we're working in the linear buffer of
117		 * the whole sg entry in the kernel's direct map rather than
118		 * within the mapped buffer of a single page, compute the
119		 * address as an offset from the page_address() of the first
120		 * page of the sg entry.  Either way the result is the address
121		 * in the direct map, but this makes it clearer what is really
122		 * going on.
123		 */
124		addr = page_address(base_page) + offset;
125	}
126
127	walk->__addr = addr;
128}
129
130/**
131 * scatterwalk_next() - Get the next data buffer in a scatterlist walk
132 * @walk: the scatter_walk
133 * @total: the total number of bytes remaining, > 0
134 *
135 * A virtual address for the next segment of data from the scatterlist will
136 * be placed into @walk->addr.  The caller must call scatterwalk_done_src()
137 * or scatterwalk_done_dst() when it is done using this virtual address.
138 *
139 * Returns: the next number of bytes available, <= @total
140 */
141static inline unsigned int scatterwalk_next(struct scatter_walk *walk,
142					    unsigned int total)
143{
144	unsigned int nbytes = scatterwalk_clamp(walk, total);
145
146	scatterwalk_map(walk);
147	return nbytes;
148}
149
150static inline void scatterwalk_unmap(struct scatter_walk *walk)
151{
152	if (IS_ENABLED(CONFIG_HIGHMEM))
153		kunmap_local(walk->__addr);
154}
155
156static inline void scatterwalk_advance(struct scatter_walk *walk,
157				       unsigned int nbytes)
158{
159	walk->offset += nbytes;
160}
161
162/**
163 * scatterwalk_done_src() - Finish one step of a walk of source scatterlist
164 * @walk: the scatter_walk
165 * @nbytes: the number of bytes processed this step, less than or equal to the
166 *	    number of bytes that scatterwalk_next() returned.
167 *
168 * Use this if the mapped address was not written to, i.e. it is source data.
169 */
170static inline void scatterwalk_done_src(struct scatter_walk *walk,
171					unsigned int nbytes)
172{
173	scatterwalk_unmap(walk);
174	scatterwalk_advance(walk, nbytes);
175}
176
177/*
178 * Flush the dcache of any pages that overlap the region
179 * [offset, offset + nbytes) relative to base_page.
180 *
181 * This should be called only when ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE, to ensure
182 * that all relevant code (including the call to sg_page() in the caller, if
183 * applicable) gets fully optimized out when !ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE.
184 */
185static inline void __scatterwalk_flush_dcache_pages(struct page *base_page,
186						    unsigned int offset,
187						    unsigned int nbytes)
188{
189	unsigned int num_pages;
190
191	base_page += offset / PAGE_SIZE;
192	offset %= PAGE_SIZE;
193
194	/*
195	 * This is an overflow-safe version of
196	 * num_pages = DIV_ROUND_UP(offset + nbytes, PAGE_SIZE).
197	 */
198	num_pages = nbytes / PAGE_SIZE;
199	num_pages += DIV_ROUND_UP(offset + (nbytes % PAGE_SIZE), PAGE_SIZE);
200
201	for (unsigned int i = 0; i < num_pages; i++)
202		flush_dcache_page(base_page + i);
203}
204
205/**
206 * scatterwalk_done_dst() - Finish one step of a walk of destination scatterlist
207 * @walk: the scatter_walk
208 * @nbytes: the number of bytes processed this step, less than or equal to the
209 *	    number of bytes that scatterwalk_next() returned.
210 *
211 * Use this if the mapped address may have been written to, i.e. it is
212 * destination data.
213 */
214static inline void scatterwalk_done_dst(struct scatter_walk *walk,
215					unsigned int nbytes)
216{
217	scatterwalk_unmap(walk);
218	if (ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE)
219		__scatterwalk_flush_dcache_pages(sg_page(walk->sg),
220						 walk->offset, nbytes);
221	scatterwalk_advance(walk, nbytes);
222}
223
224void scatterwalk_skip(struct scatter_walk *walk, unsigned int nbytes);
225
226void memcpy_from_scatterwalk(void *buf, struct scatter_walk *walk,
227			     unsigned int nbytes);
228
229void memcpy_to_scatterwalk(struct scatter_walk *walk, const void *buf,
230			   unsigned int nbytes);
231
232void memcpy_from_sglist(void *buf, struct scatterlist *sg,
233			unsigned int start, unsigned int nbytes);
234
235void memcpy_to_sglist(struct scatterlist *sg, unsigned int start,
236		      const void *buf, unsigned int nbytes);
237
238void memcpy_sglist(struct scatterlist *dst, struct scatterlist *src,
239		   unsigned int nbytes);
240
241/* In new code, please use memcpy_{from,to}_sglist() directly instead. */
242static inline void scatterwalk_map_and_copy(void *buf, struct scatterlist *sg,
243					    unsigned int start,
244					    unsigned int nbytes, int out)
245{
246	if (out)
247		memcpy_to_sglist(sg, start, buf, nbytes);
248	else
249		memcpy_from_sglist(buf, sg, start, nbytes);
250}
251
252struct scatterlist *scatterwalk_ffwd(struct scatterlist dst[2],
253				     struct scatterlist *src,
254				     unsigned int len);
255
256#endif  /* _CRYPTO_SCATTERWALK_H */