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[199.106.103.254]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-32e5ce04233sm2901973eec.22.2026.09.01.01.45.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Sep 2026 01:45:35 -0700 (PDT) Message-ID: Date: Tue, 1 Sep 2026 16:45:19 +0800 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 00/11] FBE virtualization: inline encryption for virtio-blk guests From: Linlin Zhang To: Eric Biggers Cc: axboe@kernel.dk, mst@redhat.com, jasowangio@gmail.com, James.Bottomley@hansenpartnership.com, martin.petersen@oracle.com, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, linux-block@vger.kernel.org, linux-crypto@vger.kernel.org, linux-scsi@vger.kernel.org, virtualization@lists.linux.dev, devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org, neeraj.soni@oss.qualcomm.com, gaurav.kashyap@oss.qualcomm.com, mani@kernel.org, andersson@kernel.org, konradybcio@kernel.org, bvanassche@acm.org, alim.akhtar@samsung.com, avri.altman@sandisk.com, stefanha@redhat.com, pbonzini@redhat.com, eperezma@redhat.com, xuanzhuo@linux.alibaba.com, linux-kernel@vger.kernel.org References: <20260827160806.1295313-1-linlin.zhang@oss.qualcomm.com> <20260827184219.GB2137493@google.com> <20260831210759.GE86114@quark> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-GUID: ZR8Tyr3D8y5sV2r8Qm836PKnh1rr6eOI X-Proofpoint-ORIG-GUID: ZR8Tyr3D8y5sV2r8Qm836PKnh1rr6eOI X-Proofpoint-Spam-Info: AW1haW4tMjYwOTAxMDA3NyBTYWx0ZWRfX8szrvM3kEFUQ KCreYRlOvFw1/1BWv3ATnAQeUiyq1G7c8IGfGYFxfvebxsPG2IjX0BWXLueUjZ1m8ic9rz1Bw72 cqFBO3Sso28rT6YlRIUE8dcOT7+QLaE= X-Authority-Analysis: v=2.4 cv=U8eiy+ru c=1 sm=1 tr=0 ts=6a9690b4 cx=c_pps a=MTSHoo12Qbhz2p7MsH1ifg==:117 a=JYp8KDb2vCoCEuGobkYCKw==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yx91gb_oNiZeI1HMLzn7:22 a=urKErBX1ud2WTkT0OPcA:9 a=QEXdDO2ut3YA:10 a=GvdueXVYPmCkWapjIL-Q:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTAxMDA3NyBTYWx0ZWRfX2efXMVEdiGpr GKDPuSDxPmUXn7R3RSvKxiQwNfjeL4GqNG0iGhGDxoXwLhJqR8SKSbR09syTvNaEgV0F2gAp4XZ m8h/Qxvdl9YS38b98KG3Cc/FKJrkWB6Izk65nS95mWdfKUOLllqY1y5q9JyGoDAbjiH7tIx2ynR 9H4TODv0VlXDYT1dlIRGU+LUHXRSj9L/sDb3H+bcKdgNVt/hebUQ2X27ZHXeQxoD60bzwlHHOhi sG2Ev77EJe+SVF+qm7jgHlrcdB9ePsaOYJo8GfrNKOesx91R2iYRtNL3vhahUf41GO4rV9NrZcr YHYUamnN+7BkMB7JBtzmLjcbNMXmJWwiD5RK+sCv6AabfmdSPAP3oAcMptoU+pzwgMlgOlL5CfR eU1BlPQoM+NUNmJRrJH1IThORwqYtwmyxzkI0aT1WwmTSdh9zD7UFeh7DRKZXOU9XrVdpFR8Unk QQuBfOrX7WZpd+tJYeQ== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-01_02,2026-08-31_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 spamscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609010077 On 9/1/2026 4:22 PM, Linlin Zhang wrote: > > > On 9/1/2026 5:07 AM, Eric Biggers wrote: >> On Fri, Aug 28, 2026 at 11:37:57PM +0800, Linlin Zhang wrote: >>> 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. >> >> Well, the way it should work is that each virtio-blk device should have >> its own set of *virtual* keyslots on the host side. From the guest's >> perspective it would act very similarly to UFS / eMMC inline encryption, >> and it would be easy to integrate into the existing stack. >> >> Then to process encrypted I/O, the host would use the keyslot number in >> the I/O to look up the blk_crypto_key it previously saved, and issue I/O >> using that key (using bio_crypt_set_ctx()). The existing keyslot >> management logic in the block layer would allocate or wait for a >> physical keyslot as needed, so it should just work. >> >> Eviction would similarly be passed through to blk_crypto_evict_key(). >> >> Note that with this design, there would be no static partitioning of the >> physical keyslots. The host would just allocate and release them as >> needed, similar to memory allocation. The total number of virtual >> keyslots could be greater than the number of physical keyslots. >> >> This design would also work with hardware-wrapped keys. >> >> The hardest part is still the UAPIs for the VMM to do what it needs to >> do (assuming that it even needs to support physical inline encryption >> hardware at all, and not simply use the AES acceleration on the CPU), >> but that is the case with any of the proposals. >> >> - Eric > > Thanks for your insights and clarification. > > This is a very clear architecture for virtio-blk inline encryption support > and is quite similar to what I referred to as approach 1, with a few notable > differences: > > - The host maintains a set of virtual keyslots per virtio-blk device. > - Physical keyslots are not statically partitioned. > - The virtual-to-physical slot mapping is managed as part of the virtio-blk > device implementation rather than being tied to a VM-wide slot table. > > With this design, I believe there would be two VM exits associated with > encrypted I/O: > 1. Key programming > Before encrypted I/O can be submitted, the guest needs to program a key > into a virtual keyslot: > > Guest virtio-blk driver > -> VM exit > -> virtio-blk backend (e.g. QEMU) > -> ioctl > -> host virtio-blk proxy driver > (stores the blk_crypto_key in a virtual keyslot) > > 2. Encrypted I/O submission > The I/O request carries the virtual keyslot number and DUN: > > Guest virtio-blk driver > -> VM exit > -> virtio-blk backend (e.g. QEMU) > -> ioctl > -> host virtio-blk proxy driver > (looks up the blk_crypto_key associated with the virtual keyslot > and submits I/O using bio_crypt_set_ctx()) Supplementation. This may be a potential security concern. The host virtio-blk proxy driver exposes API for key programming, the input parameters are blk_crypto key and virtual slot. If a malicious program replace the key in a specific virtual slot between key program call and I/O submission via this API, the data would be encrypted by the unintentional key. > > I have been wondering whether a model similar to the passthrough > blk-crypto-profile used by certain dm targets could be applicable here. > > In such a design, ownership of keyslot management would effectively and totally > move to the host. The guest would no longer manage virtual keyslots, and the > host block layer would continue using its existing keyslot manager to allocate, > reuse, and evict physical keyslots as needed. > > This corresponds to what I previously described as approach 2. > With this approach, encrypted I/O would require only a single VM exit: > 1. Encrypted I/O submission > The I/O request carries the blk_crypto_key and DUN: > > Guest virtio-blk driver > -> VM exit > -> virtio-blk backend (e.g. QEMU) > -> ioctl > -> host virtio-blk proxy driver > (receives the blk_crypto_key and DUN, then submits I/O using > bio_crypt_set_ctx()) > > Regardless of which approach is used, the host would still need to maintain a > key lookup table so that the host blk-crypto layer consistently sees the same > blk_crypto_key object for a guest key until that key is evicted. > > Note that, the key table format is > - approach 1: > - approach 2: > > Therefore, if transferring blk_crypto_key material from the guest to the host > (and from userspace to kernel space) is considered acceptable, I wonder whether > approach 2 might be preferable because it avoids virtual keyslots entirely and > reduces the encrypted I/O path to a single VM exit. > > Do you see any major drawbacks with such an approach? In particular, do you > think reducing the number of VM exits by eliminating virtual keyslots is a > worthwhile direction for virtio-blk inline encryption support? > > - Linlin