From: Eric Biggers <ebiggers@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Satya Tangirala <satyat@google.com>,
linux-scsi@vger.kernel.org, Kim Boojin <boojin.kim@samsung.com>,
Kuohong Wang <kuohong.wang@mediatek.com>,
Barani Muthukumaran <bmuthuku@qti.qualcomm.com>,
linux-f2fs-devel@lists.sourceforge.net,
linux-block@vger.kernel.org, linux-fscrypt@vger.kernel.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v5 7/9] fscrypt: add inline encryption support
Date: Mon, 4 Nov 2019 19:12:22 -0800 [thread overview]
Message-ID: <20191105031222.GE692@sol.localdomain> (raw)
In-Reply-To: <20191031212103.GA6244@infradead.org>
On Thu, Oct 31, 2019 at 02:21:03PM -0700, Christoph Hellwig wrote:
> > >
> > > Btw, I'm not happy about the 8-byte IV assumptions everywhere here.
> > > That really should be a parameter, not hardcoded.
> >
> > To be clear, the 8-byte IV assumption doesn't really come from fs/crypto/, but
> > rather in what the blk-crypto API provides. If blk-crypto were to provide
> > longer IV support, fs/crypto/ would pretty easily be able to make use of it.
>
> That's what I meant - we hardcode the value in fscrypt. Instead we need
> to expose the size from blk-crypt and check for it.
>
> >
> > (And if IVs >= 24 bytes were supported and we added AES-128-CBC-ESSIV and
> > Adiantum support to blk-crypto.c, then inline encryption would be able to do
> > everything that the existing filesystem-layer contents encryption can do.)
> >
> > Do you have anything in mind for how to make the API support longer IVs in a
> > clean way? Are you thinking of something like:
> >
> > #define BLK_CRYPTO_MAX_DUN_SIZE 24
> >
> > u8 dun[BLK_CRYPTO_MAX_DUN_SIZE];
> > int dun_size;
> >
> > We do have to perform arithmetic operations on it, so a byte array would make it
> > ugly and slower, but it should be possible...
>
> Well, we could make it an array of u64s, which means we can do all the
> useful arithmetics on components on one of them. But I see the point,
> this adds significant complexity for no real short term gain, and we
> should probably postponed it until needed. Maybe just document the
> assumptions a little better.
Just in case it's not obvious to anyone, I should also mention that being
limited to specifying a 64-bit DUN doesn't prevent hardware that accepts a
longer IV (e.g. 128 bits) from being used. It would just be a matter of
zero-padding the IV in the driver rather than in hardware.
The actual limitation we're talking about here is in the range of IVs that can
be specified. A 64-bit DUN only allows the first 64 bits of the IV to be
nonzero. That works for fscrypt in all cases except DIRECT_KEY policies, and it
would work for dm-crypt using the usual dm-crypt IV generator (plain64).
But for inline encryption to be compatible with DIRECT_KEY fscrypt policies or
with certain other dm-crypt IV generators, we'd need the ability to specify more
IV bits.
- Eric
next prev parent reply other threads:[~2019-11-05 3:12 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-28 7:20 [PATCH v5 0/9] Inline Encryption Support Satya Tangirala
2019-10-28 7:20 ` [PATCH v5 1/9] block: Keyslot Manager for Inline Encryption Satya Tangirala
2019-10-31 18:04 ` Christoph Hellwig
2019-10-28 7:20 ` [PATCH v5 2/9] block: Add encryption context to struct bio Satya Tangirala
2019-10-31 18:16 ` Christoph Hellwig
2019-10-28 7:20 ` [PATCH v5 3/9] block: blk-crypto for Inline Encryption Satya Tangirala
2019-10-31 17:57 ` Christoph Hellwig
2019-10-31 20:50 ` Theodore Y. Ts'o
2019-10-31 21:22 ` Christoph Hellwig
2019-11-05 2:01 ` Eric Biggers
2019-11-05 15:39 ` Christoph Hellwig
2019-10-28 7:20 ` [PATCH v5 4/9] scsi: ufs: UFS driver v2.1 spec crypto additions Satya Tangirala
2019-10-28 7:20 ` [PATCH v5 5/9] scsi: ufs: UFS crypto API Satya Tangirala
2019-10-31 18:23 ` Christoph Hellwig
2019-10-28 7:20 ` [PATCH v5 6/9] scsi: ufs: Add inline encryption support to UFS Satya Tangirala
2019-10-31 18:26 ` Christoph Hellwig
2019-10-28 7:20 ` [PATCH v5 7/9] fscrypt: add inline encryption support Satya Tangirala
2019-10-31 18:32 ` Christoph Hellwig
2019-10-31 20:21 ` Eric Biggers
2019-10-31 21:21 ` Christoph Hellwig
2019-10-31 22:25 ` Eric Biggers
2019-11-05 0:15 ` Christoph Hellwig
2019-11-05 1:03 ` Eric Biggers
2019-11-05 3:12 ` Eric Biggers [this message]
2019-10-28 7:20 ` [PATCH v5 8/9] f2fs: " Satya Tangirala
2019-10-31 17:14 ` Jaegeuk Kim
2019-10-28 7:20 ` [PATCH v5 9/9] ext4: " Satya Tangirala
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