/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Cryptographic scatter and gather helpers.
 *
 * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
 * Copyright (c) 2002 Adam J. Richter <adam@yggdrasil.com>
 * Copyright (c) 2004 Jean-Luc Cooke <jlcooke@certainkey.com>
 * Copyright (c) 2007 Herbert Xu <herbert@gondor.apana.org.au>
 */

#ifndef _CRYPTO_SCATTERWALK_H
#define _CRYPTO_SCATTERWALK_H

#include <crypto/algapi.h>

#include <linux/highmem.h>
#include <linux/mm.h>
#include <linux/scatterlist.h>

static inline void scatterwalk_crypto_chain(struct scatterlist *head,
                                            struct scatterlist *sg, int num)
{
        if (sg)
                sg_chain(head, num, sg);
        else
                sg_mark_end(head);
}

static inline void scatterwalk_start(struct scatter_walk *walk,
                                     struct scatterlist *sg)
{
        walk->sg = sg;
        walk->offset = sg->offset;
}

/*
 * This is equivalent to scatterwalk_start(walk, sg) followed by
 * scatterwalk_skip(walk, pos).
 */
static inline void scatterwalk_start_at_pos(struct scatter_walk *walk,
                                            struct scatterlist *sg,
                                            unsigned int pos)
{
        while (pos > sg->length) {
                pos -= sg->length;
                sg = sg_next(sg);
        }
        walk->sg = sg;
        walk->offset = sg->offset + pos;
}

static inline unsigned int scatterwalk_clamp(struct scatter_walk *walk,
                                             unsigned int nbytes)
{
        unsigned int len_this_sg;
        unsigned int limit;

        if (walk->offset >= walk->sg->offset + walk->sg->length)
                scatterwalk_start(walk, sg_next(walk->sg));
        len_this_sg = walk->sg->offset + walk->sg->length - walk->offset;

        /*
         * HIGHMEM case: the page may have to be mapped into memory.  To avoid
         * the complexity of having to map multiple pages at once per sg entry,
         * clamp the returned length to not cross a page boundary.
         *
         * !HIGHMEM case: no mapping is needed; all pages of the sg entry are
         * already mapped contiguously in the kernel's direct map.  For improved
         * performance, allow the walker to return data segments that cross a
         * page boundary.  Do still cap the length to PAGE_SIZE, since some
         * users rely on that to avoid disabling preemption for too long when
         * using SIMD.  It's also needed for when skcipher_walk uses a bounce
         * page due to the data not being aligned to the algorithm's alignmask.
         */
        if (IS_ENABLED(CONFIG_HIGHMEM))
                limit = PAGE_SIZE - offset_in_page(walk->offset);
        else
                limit = PAGE_SIZE;

        return min3(nbytes, len_this_sg, limit);
}

/*
 * Create a scatterlist that represents the remaining data in a walk.  Uses
 * chaining to reference the original scatterlist, so this uses at most two
 * entries in @sg_out regardless of the number of entries in the original list.
 * Assumes that sg_init_table() was already done.
 */
static inline void scatterwalk_get_sglist(struct scatter_walk *walk,
                                          struct scatterlist sg_out[2])
{
        if (walk->offset >= walk->sg->offset + walk->sg->length)
                scatterwalk_start(walk, sg_next(walk->sg));
        sg_set_page(sg_out, sg_page(walk->sg),
                    walk->sg->offset + walk->sg->length - walk->offset,
                    walk->offset);
        scatterwalk_crypto_chain(sg_out, sg_next(walk->sg), 2);
}

static inline void scatterwalk_map(struct scatter_walk *walk)
{
        struct page *base_page = sg_page(walk->sg);
        unsigned int offset = walk->offset;
        void *addr;

        if (IS_ENABLED(CONFIG_HIGHMEM)) {
                struct page *page;

                page = base_page + (offset >> PAGE_SHIFT);
                offset = offset_in_page(offset);
                addr = kmap_local_page(page) + offset;
        } else {
                /*
                 * When !HIGHMEM we allow the walker to return segments that
                 * span a page boundary; see scatterwalk_clamp().  To make it
                 * clear that in this case we're working in the linear buffer of
                 * the whole sg entry in the kernel's direct map rather than
                 * within the mapped buffer of a single page, compute the
                 * address as an offset from the page_address() of the first
                 * page of the sg entry.  Either way the result is the address
                 * in the direct map, but this makes it clearer what is really
                 * going on.
                 */
                addr = page_address(base_page) + offset;
        }

        walk->__addr = addr;
}

/**
 * scatterwalk_next() - Get the next data buffer in a scatterlist walk
 * @walk: the scatter_walk
 * @total: the total number of bytes remaining, > 0
 *
 * A virtual address for the next segment of data from the scatterlist will
 * be placed into @walk->addr.  The caller must call scatterwalk_done_src()
 * or scatterwalk_done_dst() when it is done using this virtual address.
 *
 * Returns: the next number of bytes available, <= @total
 */
static inline unsigned int scatterwalk_next(struct scatter_walk *walk,
                                            unsigned int total)
{
        unsigned int nbytes = scatterwalk_clamp(walk, total);

        scatterwalk_map(walk);
        return nbytes;
}

static inline void scatterwalk_unmap(struct scatter_walk *walk)
{
        if (IS_ENABLED(CONFIG_HIGHMEM))
                kunmap_local(walk->__addr);
}

static inline void scatterwalk_advance(struct scatter_walk *walk,
                                       unsigned int nbytes)
{
        walk->offset += nbytes;
}

/**
 * scatterwalk_done_src() - Finish one step of a walk of source scatterlist
 * @walk: the scatter_walk
 * @nbytes: the number of bytes processed this step, less than or equal to the
 *          number of bytes that scatterwalk_next() returned.
 *
 * Use this if the mapped address was not written to, i.e. it is source data.
 */
static inline void scatterwalk_done_src(struct scatter_walk *walk,
                                        unsigned int nbytes)
{
        scatterwalk_unmap(walk);
        scatterwalk_advance(walk, nbytes);
}

/*
 * Flush the dcache of any pages that overlap the region
 * [offset, offset + nbytes) relative to base_page.
 *
 * This should be called only when ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE, to ensure
 * that all relevant code (including the call to sg_page() in the caller, if
 * applicable) gets fully optimized out when !ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE.
 */
static inline void __scatterwalk_flush_dcache_pages(struct page *base_page,
                                                    unsigned int offset,
                                                    unsigned int nbytes)
{
        unsigned int num_pages;

        base_page += offset / PAGE_SIZE;
        offset %= PAGE_SIZE;

        /*
         * This is an overflow-safe version of
         * num_pages = DIV_ROUND_UP(offset + nbytes, PAGE_SIZE).
         */
        num_pages = nbytes / PAGE_SIZE;
        num_pages += DIV_ROUND_UP(offset + (nbytes % PAGE_SIZE), PAGE_SIZE);

        for (unsigned int i = 0; i < num_pages; i++)
                flush_dcache_page(base_page + i);
}

/**
 * scatterwalk_done_dst() - Finish one step of a walk of destination scatterlist
 * @walk: the scatter_walk
 * @nbytes: the number of bytes processed this step, less than or equal to the
 *          number of bytes that scatterwalk_next() returned.
 *
 * Use this if the mapped address may have been written to, i.e. it is
 * destination data.
 */
static inline void scatterwalk_done_dst(struct scatter_walk *walk,
                                        unsigned int nbytes)
{
        scatterwalk_unmap(walk);
        if (ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE)
                __scatterwalk_flush_dcache_pages(sg_page(walk->sg),
                                                 walk->offset, nbytes);
        scatterwalk_advance(walk, nbytes);
}

void scatterwalk_skip(struct scatter_walk *walk, unsigned int nbytes);

void memcpy_from_scatterwalk(void *buf, struct scatter_walk *walk,
                             unsigned int nbytes);

void memcpy_to_scatterwalk(struct scatter_walk *walk, const void *buf,
                           unsigned int nbytes);

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

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

void memcpy_sglist(struct scatterlist *dst, struct scatterlist *src,
                   unsigned int nbytes);

/* In new code, please use memcpy_{from,to}_sglist() directly instead. */
static inline void scatterwalk_map_and_copy(void *buf, struct scatterlist *sg,
                                            unsigned int start,
                                            unsigned int nbytes, int out)
{
        if (out)
                memcpy_to_sglist(sg, start, buf, nbytes);
        else
                memcpy_from_sglist(buf, sg, start, nbytes);
}

struct scatterlist *scatterwalk_ffwd(struct scatterlist dst[2],
                                     struct scatterlist *src,
                                     unsigned int len);

#endif  /* _CRYPTO_SCATTERWALK_H */