On Fri, 21 Jun 2024 at 19:31, Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > On Fri, Jun 21, 2024 at 07:06:25PM +0300, Dmitry Baryshkov wrote: > > On Fri, 21 Jun 2024 at 18:39, Eric Biggers <ebiggers@xxxxxxxxxx> wrote: > > > > > > On Fri, Jun 21, 2024 at 06:16:37PM +0300, Dmitry Baryshkov wrote: > > > > 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? > > > > > > It derives a secret for functionality such as filenames encryption that can't > > > use inline encryption. > > > > > > > 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. > > > > > > There is. That's what the BLKCRYPTOPREPAREKEY ioctl is for. > > > > > > > Some hardware might permit importing raw keys. > > > > > > That's what BLKCRYPTOIMPORTKEY is for. > > > > > > > Other hardware might insist on generating the keys on-chip so that raw keys > > > > can never be used. > > > > > > And that's what BLKCRYPTOGENERATEKEY is for. > > > > Again, this might be answered somewhere, but why can't we use keyctl > > for handling the keys and then use a single IOCTL to point the block > > device to the key in the keyring? > > All the same functionality would need to be supported, and I think that > shoehorning it into the keyrings service instead of just adding new ioctls would > be more difficult. The keyrings service was not designed for this use case. > We've already had a lot of problems trying to take advantage of the keyrings > service in fscrypt previously. The keyrings service is something that sounds > useful but really isn't all that useful. I would be really interested in reading or listening to any kind of summary or parts of the issues. I'm slightly pushy towards keyctl / keyrings, because it already provides support for different kinds of key wrapping and key management. Encrypted keys, trusted keys - those are all kinds of key management, which either will be missing or will have to be reimplemented for block layers. I know that keyrings are clumsy and not that logical, but then their API needs to be improved. Just ignoring the existing mechanisms sounds like a bad idea. > > By "a single IOCTL to point the block device to the key in the keyring", you > seem to be referring to configuring full block device encryption with a single > key. That's not something that's supported by the upstream kernel yet, and it's > not related to this patchset; currently only fscrypt supports inline encryption. I see that dm has at least some provisioning and hooks for CONFIG_BLK_INLINE_ENCRYPTION. Thus I thought that it's possible to use inline encryption through DM. > Support for it will be added at some point, which will likely indeed take the > form of an ioctl to set a key on a block device. But that would be the case > even without HW-wrapped keys. And *requiring* the key to be given in a keyring > (instead of just in a byte array passed to the ioctl) isn't very helpful, as it > just makes the API harder to use. We've learned this from the fscrypt API > already where we actually had to move away from the keyrings service in order to > fix all the issues caused by it (see FS_IOC_ADD_ENCRYPTION_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. > > > > > > That's exactly how it works. There is a block interface for specifying an > > > inline encryption key along with each bio. The submitter of the bio can specify > > > either a standard key or a HW-wrapped key. > > > > Not in this patchset. The ICE driver decides whether it can support > > HW-wrapped keys or not and then fails to support other type of keys. > > > > Sure, that's just a matter of hardware capabilities though, right? The block > layer provides a way for drivers to declare which inline encryption capabilities > they support. They can declare they support standard keys, HW-wrapped keys, > both, or neither. If Qualcomm SoCs can't support both types of keys at the same > time, that's unfortunate, but I'm not sure what your poitnt is. The user (e.g. > fscrypt) still has control over whether they use the functionality that the > hardware provides. It's a matter of policy. Harware / firmware doesn't support using both kinds of keys concurrently, if I understood Gaurav's explanations correctly. But the user should be able to make a judgement and use non-hw-wrapped keys if it fits their requirements. The driver should not make this kind of judgement. Note, this is not an issue of your original patchset, but it's a driver flaw in this patchset. -- With best wishes Dmitry
