On Fri, 21 Jun 2024 at 07:47, Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > On Thu, Jun 20, 2024 at 02:57:40PM +0300, Dmitry Baryshkov wrote: > > > > > > > > > > > Is it possible to use both kind of keys when working on standard mode? > > > > > > If not, it should be the user who selects what type of keys to be used. > > > > > > Enforcing this via DT is not a way to go. > > > > > > > > > > > > > > > > Unfortunately, that support is not there yet. When you say user, do > > > > > you mean to have it as a filesystem mount option? > > > > > > > > During cryptsetup time. When running e.g. cryptsetup I, as a user, would like > > > > to be able to use either a hardware-wrapped key or a standard key. > > > > > > > > > > What we are looking for with these patches is for per-file/folder encryption using fscrypt policies. > > > Cryptsetup to my understanding supports only full-disk , and does not support FBE (File-Based) > > > > I must admit, I mostly used dm-crypt beforehand, so I had to look at > > fscrypt now. Some of my previous comments might not be fully > > applicable. > > > > > Hence the idea here is that we mount an unencrypted device (with the inlinecrypt option that indicates inline encryption is supported) > > > And specify policies (links to keys) for different folders. > > > > > > > > The way the UFS/EMMC crypto layer is designed currently is that, this > > > > > information is needed when the modules are loaded. > > > > > > > > > > https://lore.kernel.org/all/20231104211259.17448-2-ebiggers@xxxxxxxxxx > > > > > /#Z31drivers:ufs:core:ufshcd-crypto.c > > > > > > > > I see that the driver lists capabilities here. E.g. that it supports HW-wrapped > > > > keys. But the line doesn't specify that standard keys are not supported. > > > > > > > > > > Those are capabilities that are read from the storage controller. However, wrapped keys > > > Are not a standard in the ICE JEDEC specification, and in most cases, is a value add coming > > > from the SoC. > > > > > > QCOM SOC and firmware currently does not support both kinds of keys in the HWKM mode. > > > That is something we are internally working on, but not available yet. > > > > I'd say this is a significant obstacle, at least from my point of > > view. I understand that the default might be to use hw-wrapped keys, > > but it should be possible for the user to select non-HW keys if the > > ability to recover the data is considered to be important. Note, I'm > > really pointing to the user here, not to the system integrator. So > > using DT property or specifying kernel arguments to switch between > > these modes is not really an option. > > > > But I'd really love to hear some feedback from linux-security and/or > > linux-fscrypt here. > > > > In my humble opinion the user should be able to specify that the key > > is wrapped using the hardware KMK. Then if the hardware has already > > started using the other kind of keys, it should be able to respond > > with -EINVAL / whatever else. Then the user can evict previously > > programmed key and program a desired one. > > > > > > Also, I'd have expected that hw-wrapped keys are handled using trusted > > > > keys mechanism (see security/keys/trusted-keys/). Could you please point > > > > out why that's not the case? > > > > > > > > > > I will evaluate this. > > > But my initial response is that we currently cannot communicate to our TPM directly from HLOS, but > > > goes through QTEE, and I don't think our qtee currently interfaces with the open source tee > > > driver. The interface is through QCOM SCM driver. > > > > Note, this is just an API interface, see how it is implemented for the > > CAAM hardware. > > > > The problem is that this patchset was sent out without the patches that add the > block and filesystem-level framework for hardware-wrapped inline encryption > keys, which it depends on. So it's lacking context. The proposed framework can > be found at > https://lore.kernel.org/linux-block/20231104211259.17448-1-ebiggers@xxxxxxxxxx/T/#u Thank you. I have quickly skimmed through the patches, but I didn't review them thoroughly. Maybe the patchset already implements the interfaces that I'm thinking about. In such a case please excuse me. I will give it a more thorough look later today. > As for why "trusted keys" aren't used, they just aren't helpful here. "Trusted > keys" are based around a model where the kernel can request that keys be sealed > and unsealed using a trust source, and the kernel gets access to the raw > unsealed keys. Hardware-wrapped inline encryption keys use a different model > where the kernel never gets access to the raw keys. They also have the concept > of ephemeral wrapping which does not exist in "trusted keys". And they need to > be properly integrated with the inline encryption framework in the block layer. Then what exactly does qcom_scm_derive_sw_secret() do? Does it rewrap the key under some other key? I had the feeling that there are two separate pieces of functionality being stuffed into a single patchset and into a single solution. First one is handling the keys. I keep on thinking that there should be a separate software interface to unseal the key and rewrap it under an ephemeral key. Some hardware might permit importing raw keys. Other hardware might insist on generating the keys on-chip so that raw keys can never be used. Anyway, the net result is the binary blob + cookie for the ephemeral key. Second part is the actual block interface. Gaurav wrote about targeting fscrypt, but there should be no actual difference between crypto targets. FDE or having a single partition encrypted should probably work in the same way. Convert the key into blk_crypto_key (including the cookie for the ephemeral key), program the key into the slot, use the slot to en/decrypt hardware blocks. My main point is that the decision on the key type should be coming from the user. I can easily imagine a user, which wants to use password / raw key for documents storage so that it is possible to recover the data, hw-wrapped long-term key for app & data storage and generated one-time random key for the swap, so that memory contents can never be recovered after reboot / device capture. -- With best wishes Dmitry
