On Tue, Sep 01, 2026 at 05:21:53PM +0800, Linlin Zhang wrote: > > > On 9/1/2026 4:41 AM, Stefan Hajnoczi wrote: > > On Fri, Aug 28, 2026 at 11:37:57PM +0800, Linlin Zhang wrote: > >> > >> > >> 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. > > > > Yes, userspace shouldn't have access to the entire physical key slot > > range. The host kernel or other VMs may need key slots and an untrusted > > QEMU process must not be able to modify those key slots or use them for > > I/O. > > > > The uapi design should include a solution for this. For example, there > > could be an ioctl like BLKCRYPTOSEALKEYS that permanently restricts the > > key range on this block device file descriptor and cannot be undone. > > Libvirt or other management tooling would call this ioctl with > > CAP_SYS_ADMIN before passing the file descriptor when launching QEMU > > without CAP_SYS_ADMIN. This prevents QEMU from ever having access to the > > full physical key range. > > > > Just an idea. Those familiar with blk-crypto may have a better one. It > > seems likely that we can find a design that matches the level of > > security of the out-of-band approach. > > Thanks for your comment! > > Eric mentioned a proposal that each virtio block device has its own *virtual* > keyslots in the host, which is not static partitioning of the physical > keyslots. > I have concerns about the new key programing UAPI and 2 VM exits per encrypted > I/O. I'll confirm with Eric if that needs be considered and if we need pass > through the crypto to the host blk-crypto-profile (which means the max slots > of blk-crypto-profile in the guest is 0, and virtio block driver only doesn't > implement the key program interface in blk_crypto_ll_ops). > > > > >> > >> 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. > > > > This sounds like an approach that skips key programming and instead > > sends the keys along with each I/O request. The device implementation is > > responsible for managing key slots on the physical ICE. My main concern > > with this would be whether the blk_crypto_ll_ops semantics can be > > faithfully replicated (e.g. error reporting) without explicit key > > programming operations. > > > > Stefan > > You're right. When the virtio-blk device processes encrypted I/O, it > would be responsible for extracting the blk_crypto_key and DUN from the > virtqueue and attaching them to the bio (via bio_crypt_set_ctx()). The > existing keyslot management logic in the block layer would then handle > physical keyslot allocation and waiting as needed, so the rest of the > blk-crypto infrastructure should continue to work unchanged. > > Regarding your concern, there is already a somewhat similar > implementation in the device-mapper layer ( > dm_table_construct_crypto_profile() implements a passthrough > blk_crypto_ll_ops profile. See > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/md/dm-table.c?h=v7.3-rc1 > ). > > Based on my current understanding, I don't see any obvious > architectural issues with this approach. However, I may be missing > something, so I'd appreciate any feedback if you see flaws in the > design or potential problems that should be taken into account.
I don't have enough blk-crypto knowledge to give good feedback on the details of this approach, but Eric and others could help with that. Stefan
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