Re: [Qemu-devel] [PATCH v2 11/13] qcrypto-luks: refactoring: simplify the math used for keyslot locations

[Maxim Levitsky]

On Fri, 2019-09-06 at 14:17 +0100, Daniel P. Berrangé wrote:
> On Mon, Aug 26, 2019 at 04:51:01PM +0300, Maxim Levitsky wrote:
> > Signed-off-by: Maxim Levitsky <address@hidden>
> > ---
> >  crypto/block-luks.c | 64 +++++++++++++++++++++++++++++----------------
> >  1 file changed, 41 insertions(+), 23 deletions(-)
> > 
> > diff --git a/crypto/block-luks.c b/crypto/block-luks.c
> > index d713125925..6a43d97ce5 100644
> > --- a/crypto/block-luks.c
> > +++ b/crypto/block-luks.c
> > @@ -409,6 +409,32 @@ qcrypto_block_luks_essiv_cipher(QCryptoCipherAlgorithm 
> > cipher,
> >      }
> >  }
> >  
> > +/*
> > + * Returns number of sectors needed to store the key material
> > + * given number of anti forensic stripes
> > + */
> > +static int
> > +qcrypto_block_luks_splitkeylen_sectors(const QCryptoBlockLUKS *luks,
> > +                                       unsigned int stripes)
> > +{
> > +    /*
> > +     * This calculation doesn't match that shown in the spec,
> > +     * but instead follows the cryptsetup implementation.
> > +     */
> > +
> > +    size_t header_sectors = QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> > +        QCRYPTO_BLOCK_LUKS_SECTOR_SIZE;
> 
> The caller already calculated that so just pass it in

All right, no problem.

> 
> > +
> > +    size_t splitkeylen = luks->header.master_key_len * stripes;
> > +
> > +    /* First align the key material size to block size*/
> > +    size_t splitkeylen_sectors =
> > +        DIV_ROUND_UP(splitkeylen, QCRYPTO_BLOCK_LUKS_SECTOR_SIZE);
> > +
> > +    /* Then also align the key material size to the size of the header */
> > +    return ROUND_UP(splitkeylen_sectors, header_sectors);
> > +}
> > +
> >  /*
> >   * Stores the main LUKS header, taking care of endianess
> >   */
> > @@ -1151,7 +1177,8 @@ qcrypto_block_luks_create(QCryptoBlock *block,
> >      QCryptoBlockCreateOptionsLUKS luks_opts;
> >      Error *local_err = NULL;
> >      g_autofree uint8_t *masterkey = NULL;
> > -    size_t splitkeylen = 0;
> > +    size_t header_sectors;
> > +    size_t split_key_sectors;
> >      size_t i;
> >      g_autofree char *password;
> >      const char *cipher_alg;
> > @@ -1370,37 +1397,28 @@ qcrypto_block_luks_create(QCryptoBlock *block,
> >          goto error;
> >      }
> >  
> > +    /* start with the sector that follows the header*/
> > +    header_sectors = QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> > +        QCRYPTO_BLOCK_LUKS_SECTOR_SIZE;
> > +
> > +    split_key_sectors =
> > +        qcrypto_block_luks_splitkeylen_sectors(luks,
> > +                                               QCRYPTO_BLOCK_LUKS_STRIPES);
> >  
> > -    /* Although LUKS has multiple key slots, we're just going
> > -     * to use the first key slot */
> > -    splitkeylen = luks->header.master_key_len * QCRYPTO_BLOCK_LUKS_STRIPES;
> >      for (i = 0; i < QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS; i++) {
> > -        luks->header.key_slots[i].active = 
> > QCRYPTO_BLOCK_LUKS_KEY_SLOT_DISABLED;
> > -        luks->header.key_slots[i].stripes = QCRYPTO_BLOCK_LUKS_STRIPES;
> > +        QCryptoBlockLUKSKeySlot *slot = &luks->header.key_slots[i];
> > +        slot->active = QCRYPTO_BLOCK_LUKS_KEY_SLOT_DISABLED;
> >  
> > -        /* This calculation doesn't match that shown in the spec,
> > -         * but instead follows the cryptsetup implementation.
> > -         */
> > -        luks->header.key_slots[i].key_offset_sector =
> > -            (QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> > -             QCRYPTO_BLOCK_LUKS_SECTOR_SIZE) +
> > -            (ROUND_UP(DIV_ROUND_UP(splitkeylen, 
> > QCRYPTO_BLOCK_LUKS_SECTOR_SIZE),
> > -                      (QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> > -                       QCRYPTO_BLOCK_LUKS_SECTOR_SIZE)) * i);
> > +        slot->key_offset_sector = header_sectors + i * split_key_sectors;
> > +        slot->stripes = QCRYPTO_BLOCK_LUKS_STRIPES;
> >      }
> >  
> > -
> >      /* The total size of the LUKS headers is the partition header + key
> >       * slot headers, rounded up to the nearest sector, combined with
> >       * the size of each master key material region, also rounded up
> >       * to the nearest sector */
> > -    luks->header.payload_offset_sector =
> > -        (QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> > -         QCRYPTO_BLOCK_LUKS_SECTOR_SIZE) +
> > -        (ROUND_UP(DIV_ROUND_UP(splitkeylen, 
> > QCRYPTO_BLOCK_LUKS_SECTOR_SIZE),
> > -                  (QCRYPTO_BLOCK_LUKS_KEY_SLOT_OFFSET /
> > -                   QCRYPTO_BLOCK_LUKS_SECTOR_SIZE)) *
> > -         QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS);
> > +    luks->header.payload_offset_sector = header_sectors +
> > +            QCRYPTO_BLOCK_LUKS_NUM_KEY_SLOTS * split_key_sectors;
> >  
> >      block->sector_size = QCRYPTO_BLOCK_LUKS_SECTOR_SIZE;
> >      block->payload_offset = luks->header.payload_offset_sector *
> 
> Reviewed-by: Daniel P. Berrangé <address@hidden>
> 
> Regards,
> Daniel

Best regards,
        Maxim Levitsky