linux/crypto/scatterwalk.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Cryptographic API.
 *
 * Cipher operations.
 *
 * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
 *               2002 Adam J. Richter <adam@yggdrasil.com>
 *               2004 Jean-Luc Cooke <jlcooke@certainkey.com>
 */

#include <crypto/scatterwalk.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/scatterlist.h>

void scatterwalk_skip(struct scatter_walk *walk, unsigned int nbytes)
{
	struct scatterlist *sg = walk->sg;

	nbytes += walk->offset - sg->offset;

	while (nbytes > sg->length) {
		nbytes -= sg->length;
		sg = sg_next(sg);
	}
	walk->sg = sg;
	walk->offset = sg->offset + nbytes;
}
EXPORT_SYMBOL_GPL(scatterwalk_skip);

inline void memcpy_from_scatterwalk(void *buf, struct scatter_walk *walk,
				    unsigned int nbytes)
{
	do {
		unsigned int to_copy;

		to_copy = scatterwalk_next(walk, nbytes);
		memcpy(buf, walk->addr, to_copy);
		scatterwalk_done_src(walk, to_copy);
		buf += to_copy;
		nbytes -= to_copy;
	} while (nbytes);
}
EXPORT_SYMBOL_GPL(memcpy_from_scatterwalk);

inline void memcpy_to_scatterwalk(struct scatter_walk *walk, const void *buf,
				  unsigned int nbytes)
{
	do {
		unsigned int to_copy;

		to_copy = scatterwalk_next(walk, nbytes);
		memcpy(walk->addr, buf, to_copy);
		scatterwalk_done_dst(walk, to_copy);
		buf += to_copy;
		nbytes -= to_copy;
	} while (nbytes);
}
EXPORT_SYMBOL_GPL(memcpy_to_scatterwalk);

void memcpy_from_sglist(void *buf, struct scatterlist *sg,
			unsigned int start, unsigned int nbytes)
{
	struct scatter_walk walk;

	if (unlikely(nbytes == 0)) /* in case sg == NULL */
		return;

	scatterwalk_start_at_pos(&walk, sg, start);
	memcpy_from_scatterwalk(buf, &walk, nbytes);
}
EXPORT_SYMBOL_GPL(memcpy_from_sglist);

void memcpy_to_sglist(struct scatterlist *sg, unsigned int start,
		      const void *buf, unsigned int nbytes)
{
	struct scatter_walk walk;

	if (unlikely(nbytes == 0)) /* in case sg == NULL */
		return;

	scatterwalk_start_at_pos(&walk, sg, start);
	memcpy_to_scatterwalk(&walk, buf, nbytes);
}
EXPORT_SYMBOL_GPL(memcpy_to_sglist);

/**
 * memcpy_sglist() - Copy data from one scatterlist to another
 * @dst: The destination scatterlist.  Can be NULL if @nbytes == 0.
 * @src: The source scatterlist.  Can be NULL if @nbytes == 0.
 * @nbytes: Number of bytes to copy
 *
 * The scatterlists can describe exactly the same memory, in which case this
 * function is a no-op.  No other overlaps are supported.
 *
 * Context: Any context
 */
void memcpy_sglist(struct scatterlist *dst, struct scatterlist *src,
		   unsigned int nbytes)
{
	unsigned int src_offset, dst_offset;

	if (unlikely(nbytes == 0)) /* in case src and/or dst is NULL */
		return;

	src_offset = src->offset;
	dst_offset = dst->offset;
	for (;;) {
		/* Compute the length to copy this step. */
		unsigned int len = min3(src->offset + src->length - src_offset,
					dst->offset + dst->length - dst_offset,
					nbytes);
		struct page *src_page = sg_page(src);
		struct page *dst_page = sg_page(dst);
		const void *src_virt;
		void *dst_virt;

		if (IS_ENABLED(CONFIG_HIGHMEM)) {
			/* HIGHMEM: we may have to actually map the pages. */
			const unsigned int src_oip = offset_in_page(src_offset);
			const unsigned int dst_oip = offset_in_page(dst_offset);
			const unsigned int limit = PAGE_SIZE;

			/* Further limit len to not cross a page boundary. */
			len = min3(len, limit - src_oip, limit - dst_oip);

			/* Compute the source and destination pages. */
			src_page += src_offset / PAGE_SIZE;
			dst_page += dst_offset / PAGE_SIZE;

			if (src_page != dst_page) {
				/* Copy between different pages. */
				memcpy_page(dst_page, dst_oip,
					    src_page, src_oip, len);
				flush_dcache_page(dst_page);
			} else if (src_oip != dst_oip) {
				/* Copy between different parts of same page. */
				dst_virt = kmap_local_page(dst_page);
				memcpy(dst_virt + dst_oip, dst_virt + src_oip,
				       len);
				kunmap_local(dst_virt);
				flush_dcache_page(dst_page);
			} /* Else, it's the same memory.  No action needed. */
		} else {
			/*
			 * !HIGHMEM: no mapping needed.  Just work in the linear
			 * buffer of each sg entry.  Note that we can cross page
			 * boundaries, as they are not significant in this case.
			 */
			src_virt = page_address(src_page) + src_offset;
			dst_virt = page_address(dst_page) + dst_offset;
			if (src_virt != dst_virt) {
				memcpy(dst_virt, src_virt, len);
				if (ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE)
					__scatterwalk_flush_dcache_pages(
						dst_page, dst_offset, len);
			} /* Else, it's the same memory.  No action needed. */
		}
		nbytes -= len;
		if (nbytes == 0) /* No more to copy? */
			break;

		/*
		 * There's more to copy.  Advance the offsets by the length
		 * copied this step, and advance the sg entries as needed.
		 */
		src_offset += len;
		if (src_offset >= src->offset + src->length) {
			src = sg_next(src);
			src_offset = src->offset;
		}
		dst_offset += len;
		if (dst_offset >= dst->offset + dst->length) {
			dst = sg_next(dst);
			dst_offset = dst->offset;
		}
	}
}
EXPORT_SYMBOL_GPL(memcpy_sglist);

struct scatterlist *scatterwalk_ffwd(struct scatterlist dst[2],
				     struct scatterlist *src,
				     unsigned int len)
{
	for (;;) {
		if (!len)
			return src;

		if (src->length > len)
			break;

		len -= src->length;
		src = sg_next(src);
	}

	sg_init_table(dst, 2);
	sg_set_page(dst, sg_page(src), src->length - len, src->offset + len);
	scatterwalk_crypto_chain(dst, sg_next(src), 2);

	return dst;
}
EXPORT_SYMBOL_GPL(scatterwalk_ffwd);