Re: [PATCH v7 2/8] blk-crypto: don't require user buffer alignment

Eric Biggers
2020-11-17T23:51:52Z

On Tue, Nov 17, 2020 at 02:07:02PM +0000, Satya Tangirala wrote:
> Previously, blk-crypto-fallback required the offset and length of each bvec
> in a bio to be aligned to the crypto data unit size. This patch enables
> blk-crypto-fallback to work even if that's not the case - the requirement
> now is only that the total length of the data in the bio is aligned to
> the crypto data unit size.
>
> Now that blk-crypto-fallback can handle bvecs not aligned to crypto data
> units, and we've ensured that bios are not split in the middle of a
> crypto data unit, we can relax the alignment check done by blk-crypto.

I think the blk-crypto.c and blk-crypto-fallback.c changes belong in different
patches.

There should also be a brief explanation of why this is needed (make the
alignment requirements on direct I/O to encrypted files somewhat more similar to
standard unencrypted files, right)?.

Also, how were the blk-crypto-fallback changes tested?

> @@ -305,45 +374,57 @@ static bool blk_crypto_fallback_encrypt_bio(struct bio **bio_ptr)
> }
>
> memcpy(curr_dun, bc->bc_dun, sizeof(curr_dun));
> - sg_init_table(&src, 1);
> - sg_init_table(&dst, 1);
>
> - skcipher_request_set_crypt(ciph_req, &src, &dst, data_unit_size,
> + skcipher_request_set_crypt(ciph_req, src, dst, data_unit_size,
> iv.bytes);
>
> - /* Encrypt each page in the bounce bio */
> + /*
> + * Encrypt each data unit in the bounce bio.
> + *
> + * Take care to handle the case where a data unit spans bio segments.
> + * This can happen when data_unit_size > logical_block_size.
> + */
> for (i = 0; i < enc_bio->bi_vcnt; i++) {
> - struct bio_vec *enc_bvec = &enc_bio->bi_io_vec[i];
> - struct page *plaintext_page = enc_bvec->bv_page;
> + struct bio_vec *bv = &enc_bio->bi_io_vec[i];
> + struct page *plaintext_page = bv->bv_page;
> struct page *ciphertext_page =
> mempool_alloc(blk_crypto_bounce_page_pool, GFP_NOIO);
> + unsigned int offset_in_bv = 0;
>
> - enc_bvec->bv_page = ciphertext_page;
> + bv->bv_page = ciphertext_page;
>
> if (!ciphertext_page) {
> src_bio->bi_status = BLK_STS_RESOURCE;
> goto out_free_bounce_pages;
> }
>
> - sg_set_page(&src, plaintext_page, data_unit_size,
> - enc_bvec->bv_offset);
> - sg_set_page(&dst, ciphertext_page, data_unit_size,
> - enc_bvec->bv_offset);
> -
> - /* Encrypt each data unit in this page */
> - for (j = 0; j < enc_bvec->bv_len; j += data_unit_size) {
> - blk_crypto_dun_to_iv(curr_dun, &iv);
> - if (crypto_wait_req(crypto_skcipher_encrypt(ciph_req),
> - &wait)) {
> - i++;
> - src_bio->bi_status = BLK_STS_IOERR;
> - goto out_free_bounce_pages;
> + while (offset_in_bv < bv->bv_len) {
> + unsigned int n = min(bv->bv_len - offset_in_bv,
> + data_unit_size - du_filled);
> + sg_set_page(&src[sg_idx], plaintext_page, n,
> + bv->bv_offset + offset_in_bv);
> + sg_set_page(&dst[sg_idx], ciphertext_page, n,
> + bv->bv_offset + offset_in_bv);
> + sg_idx++;
> + offset_in_bv += n;
> + du_filled += n;
> + if (du_filled == data_unit_size) {
> + blk_crypto_dun_to_iv(curr_dun, &iv);
> + if (crypto_wait_req(crypto_skcipher_encrypt(ciph_req),
> + &wait)) {
> + src_bio->bi_status = BLK_STS_IOERR;
> + goto out_free_bounce_pages;
> + }
> + bio_crypt_dun_increment(curr_dun, 1);
> + sg_idx = 0;
> + du_filled = 0;

This is leaking a bounce page if crypto_skcipher_encrypt() fails. This can be
fixed either by keeping the 'i++' that was on the error path before, or by
moving the i++ in the for statement to just below to where the bounce page was
successfully allocated.

- Eric