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Date: Fri, 21 Jun 2024 15:35:40 +0000
From: Gaurav Kashyap <gaurkash@....qualcomm.com>
To: Eric Biggers <ebiggers@...nel.org>,
        "dmitry.baryshkov@...aro.org"
	<dmitry.baryshkov@...aro.org>
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Subject: RE: [PATCH v5 04/15] soc: qcom: ice: add hwkm support in ice

Hello Eric

On 06/20/2024, 9:48 PM PDT, Eric Biggers 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@kern
> > > > > el.org /#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@...nel.org/T/#u
> 

I have only been adding the fscryp patch link as part of the cover letter - as a dependency.
https://lore.kernel.org/all/20240617005825.1443206-1-quic_gaurkash@quicinc.com/
If you would like me to include it in the patch series itself, I can do that as well.

> 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.
> 
> - Eric

Regards,
Gaurav

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