On 8/28/2026 2:42 AM, Eric Biggers wrote:
> On Thu, Aug 27, 2026 at 09:07:09AM -0700, Linlin Zhang wrote:
>> From: linlzhan <[email protected]>
>>
>> Current virtio-blk does not provide a mechanism for a guest to
>> program hardware keys or submit encrypted I/O using pre-programmed
>> keyslots. It drops the crypto context when issuing a bio request
>> to the virtio-blk queue, preventing inline-encryption-based FBE
>> on virtio block devices.
>>
>> This series enables File-Based Encryption in guest VMs on Qualcomm
>> GVM platforms where the ICE inline encryption hardware is shared
>> between the host and guests. In this environment the guest kernel
>> has no access to the ICE hardware directly; it supplies a virtual
>> keyslot index and data unit number with each encrypted I/O request
>> via VIRTIO_BLK_F_INLINE_ENCRYPTION, and the host must translate the
>> virtual slot to a physical ICE keyslot and submit the bio — without
>> transferring raw key material across the VM boundary.
>
> This seems to be designed incorrectly by not making virtio-blk itself
> support key programming and eviction. That complicates things
> significantly by then having to handle the key programming and eviction
> out-of-band using Qualcomm-specific SCM calls. It also means that
> adding other implementations of this would be very difficult.
>
> There are some claims that not transmitting keys across the VM boundary
> is desirable. But that doesn't seem meaningful, given that all the I/O
> is transmitted across that boundary in plaintext anyway, and also it
> seems that hardware-wrapped keys will be supported too.
>
> Please make virtio-blk support the key programming, eviction, and
> HW-wrapped key management operations that are needed for this to work.
>
> - Eric
Thanks for your comments!
Not making virtio-blk itself support key programming and eviction is
something done deliberately. Based on that HW-wrapped key management
operations are also handled in the out-of-band path.
There are bellow 2 approaches I investigated to let virtio-blk programming
the key.
1. virtio_blk implements blk_crypto_ll_ops interfaces, including program
key and evict key interfaces.(Same to 'the virtio-blk interface
standardized
blk_crypto_ll_ops requests' mentioned by Stefan in the virtio SPEC thread)
The guest's block crypto profile manages the keyslot in virtual slot
format in this scenario.
- block crypto key and virt_slot index it passed to the hypervisor's
(EL2) device emulation (QEMU, using QEMU in the following) which
runs in userspace of the host. Besides of transferring the virtual
slot to the physical slot, a programming block crypto key UAPI need
be added. Follow current blk-crypto design, it may be like
BLKCRYPTOGENERATEKEY. I thought this results in a security risk that
allows userspace process a key into a key slot.
- For key eviction, it's similar to above key programming handling, also
need a key eviction in blk IOCTLs, but leads to the security risk
that allow userspace client to evict a key in a key slot.
virt_slot, DUN and DUSize is appended to virtblk request during crypto
I/O.
2. virtio_blk implements blk_crypto_ll_ops interfaces, excluding program
key and evict key interfaces.
The guest's block crypto profile doesn't manage keyslot for the guest,
the host's block crypto profile manages keyslot for both the guest and
the host. The trigger of key programming operation is moved from the
guest to the host.
- The whole block crypto key (key size, key bytes, blk_crypto_config)
and DUN are appended to the virtblk request during IO, a little
high payload.
The backend parses the crypto message in the virtio queue and
construct a block crypto key and DUN for the bio_crypto_ctx
set to the BIO. So that the IO flow in the host can program
the key.
The question is that the blk-crypto-profile distinguishs the
block crypto key via the key's address. But the host has
different key addresses for the programming and eviction key
operations of the same block crypto key from GVM, because the
key is re-constructed in the host for the key program and
eviction operations.
To fix it, the approach I thought is maintaining a new key
hash table in the backend, and comparing the block crypto key
content and DUN parsed from virtio queue with that in the key
hash table.
My major concern is that this need keep the keys synchronization
b/w this new hash table and the blk-crypto-profile's hash table
carefully, avoiding that key is still present in the
blk-crypto-profile's hash table, but removed in backend hash
table. Another point is that the whole block crypto key and
DUN are appended into virtio block request per crypto I/O.
- For key eviction, adding a key eviction in blk IOCTLs allows
userspace client to evict a key in a key slot. I thought this
is a security concern.
This option doesn't need map virt_slot to physical one.
Taking all the above into account, I made a compromise to implement
blk_crypto_ll_ops interfaces in a out-of-band path, which lets the virtio
blk only need focus on the data path. I agree that it is complex than
the second option mentioned in the above, but small payload (only
virt_slot, DUN, DUSize) in the virtio block request and no security
risk of key eviction from userspace.
I would like to hear your thoughts about the above and am appreciated
if you could share your insights about the design of inline
encryption in virtio block.
Regards,
Linlin
