Re: [Qemu-devel] [PATCH v3 4/7] block: don't use constant 512 as sector size in crypto driver

["Daniel P. Berrange" <berrange@redhat.com>]

On Sat, Sep 16, 2017 at 06:24:56PM +0200, Max Reitz wrote:
> On 2017-09-12 13:28, Daniel P. Berrange wrote:
> > Use the qcrypto_block_get_sector_size() value in the block
> > crypto driver instead of hardcoding 512 as the sector size.
> > 
> > Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> > ---
> >  block/crypto.c | 34 ++++++++++++++++++----------------
> >  1 file changed, 18 insertions(+), 16 deletions(-)
> > 
> > diff --git a/block/crypto.c b/block/crypto.c
> > index d68cbac2ac..49d6d4c058 100644
> > --- a/block/crypto.c
> > +++ b/block/crypto.c
> > @@ -392,8 +392,9 @@ block_crypto_co_readv(BlockDriverState *bs, int64_t sector_num,
> >      uint8_t *cipher_data = NULL;
> >      QEMUIOVector hd_qiov;
> >      int ret = 0;
> > +    uint64_t sector_size = qcrypto_block_get_sector_size(crypto->block);
> >      uint64_t payload_offset =
> > -        qcrypto_block_get_payload_offset(crypto->block) / 512;
> > +        qcrypto_block_get_payload_offset(crypto->block) / sector_size;
> >      assert(payload_offset < (INT64_MAX / 512));
> >  
> >      qemu_iovec_init(&hd_qiov, qiov->niov);
> > @@ -401,9 +402,9 @@ block_crypto_co_readv(BlockDriverState *bs, int64_t sector_num,
> >      /* Bounce buffer because we don't wish to expose cipher text
> >       * in qiov which points to guest memory.
> >       */
> > -    cipher_data =
> > -        qemu_try_blockalign(bs->file->bs, MIN(BLOCK_CRYPTO_MAX_SECTORS * 512,
> > -                                              qiov->size));
> > +    cipher_data = qemu_try_blockalign(
> > +        bs->file->bs, MIN(BLOCK_CRYPTO_MAX_SECTORS * sector_size,
> > +                          qiov->size));
> >      if (cipher_data == NULL) {
> >          ret = -ENOMEM;
> >          goto cleanup;
> > @@ -417,7 +418,7 @@ block_crypto_co_readv(BlockDriverState *bs, int64_t sector_num,
> >          }
> >  
> >          qemu_iovec_reset(&hd_qiov);
> > -        qemu_iovec_add(&hd_qiov, cipher_data, cur_nr_sectors * 512);
> > +        qemu_iovec_add(&hd_qiov, cipher_data, cur_nr_sectors * sector_size);
> 
> cur_nr_sectors is based on remaining_sectors; which in turn is a
> parameter to this function and comes from the block layer.  Therefore
> its unit is BDRV_SECTOR_SIZE and not the crypto driver's sector size.
> 
> Same in the hunk below, and in block_crypto_co_writev().
> 
> >  
> >          ret = bdrv_co_readv(bs->file,
> >                              payload_offset + sector_num,
> 
> Same thing here, albeit in a different variation: The unit of this
> parameter of bdrv_co_readv() (start sector index) is a block layer
> sector, whose size is always BDRV_SECTOR_SIZE.
> 
> Therefore you cannot divide the result from
> qcrypto_block_get_payload_offset() by the crypto driver's sector size
> and then use it as a sector index here.
> 
> Same in block_crypto_co_writev().
> 
> 
> I assume that you fix this in the next patch, but for now it's just wrong.

Yeah, in retrospect I should have kept this patch using BDRV_SECTOR_SIZE
throughout as previous versions had it, so I'm going to go back to doing
that. Only use the encryption sector size in a later patch where we have
already switched to doing byte based I/O.


Regards,
Daniel
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