Re: [PATCH 0/4] keys: Introduce a keys frontend for attestation reports

[Dan Williams]

Jarkko Sakkinen wrote:
> On Fri Jul 28, 2023 at 7:44 PM UTC, Dan Williams wrote:
> > Jarkko Sakkinen wrote:
> > > On Fri Jul 28, 2023 at 7:30 PM UTC, Dan Williams wrote:
> > > > The bulk of the justification for this patch kit is in "[PATCH 1/4]
> > > 
> > > /patch kit/patch set/
> > > 
> > > > keys: Introduce tsm keys". The short summary is that the current
> > > > approach of adding new char devs and new ioctls, for what amounts to the
> > > > same functionality with minor formatting differences across vendors, is
> > > > untenable. Common concepts and the community benefit from common
> > > > infrastructure.
> > > >
> > > > Use Keys to build common infrastructure for confidential computing
> > > 
> > > /Keys/Linux keyring/
> > > 
> > > > attestation report blobs, convert sevguest to use it (leaving the
> > > > deprecation question alone for now), and pave the way for tdx-guest and
> > > > the eventual risc-v equivalent to use it in lieu of new ioctls.
> > > >
> > > > The sevguest conversion is only compile-tested.
> > > >
> > > > This submission is To:David since he needs to sign-off on the idea of a
> > > > new Keys type, the rest is up to the confidential-computing driver
> > > > maintainers to adopt.
> > > >
> > > > Changes from / credit for internal review:
> > > > - highlight copy_{to,from}_sockptr() as a common way to mix
> > > >   copy_user() and memcpy() paths (Andy)
> > > > - add MODULE_DESCRIPTION() (Andy)
> > > > - clarify how the user-defined portion blob might be used (Elena)
> > > > - clarify the key instantiation options (Sathya)
> > > > - drop usage of a list for registering providers (Sathya)
> > > > - drop list.h include from tsm.h (Andy)
> > > > - add a comment for how TSM_DATA_MAX was derived (Andy)
> > > > - stop open coding kmemdup_nul() (Andy)
> > > > - add types.h to tsm.h (Andy)
> > > > - fix punctuation in comment (Andy)
> > > > - reorder security/keys/Makefile (Andy)
> > > > - add some missing includes to tsm.c (Andy)
> > > > - undo an 81 column clang-format line break (Andy)
> > > > - manually reflow tsm_token indentation (Andy)
> > > > - move allocations after input validation in tsm_instantiate() (Andy)
> > > > - switch to bin2hex() in tsm_read() (Andy)
> > > > - move init/exit declarations next to their functions (Andy)
> > > >
> > > >
> > > > ---
> > > >
> > > > Dan Williams (4):
> > > >       keys: Introduce tsm keys
> > > >       virt: sevguest: Prep for kernel internal {get,get_ext}_report()
> > > >       mm/slab: Add __free() support for kvfree
> > > >       virt: sevguest: Add TSM key support for SNP_{GET,GET_EXT}_REPORT
> > > >
> > > >
> > > >  drivers/virt/coco/sev-guest/Kconfig     |    2 
> > > >  drivers/virt/coco/sev-guest/sev-guest.c |  135 ++++++++++++++-
> > > >  include/keys/tsm.h                      |   71 ++++++++
> > > >  include/linux/slab.h                    |    2 
> > > >  security/keys/Kconfig                   |   12 +
> > > >  security/keys/Makefile                  |    1 
> > > >  security/keys/tsm.c                     |  282 +++++++++++++++++++++++++++++++
> > > >  7 files changed, 494 insertions(+), 11 deletions(-)
> > > >  create mode 100644 include/keys/tsm.h
> > > >  create mode 100644 security/keys/tsm.c
> > > >
> > > > base-commit: 06c2afb862f9da8dc5efa4b6076a0e48c3fbaaa5
> > > 
> > > So how does this scale? Does it scale to TDX, SGX, TPM's or even TEE's
> > > (ARM SM, RISC-V Keystone etc.). I'm not sure about the scope but we want
> > > of course something that adapts to multiple use cases, right?
> >
> > TPMs and TEEs are covered by trusted-keys. I do think a "TSM" flavor of
> > trusted-keys is in scope for where some of these implementations are
> > headed, but that comes later. I talk about that in the changelog that
> > functionality like SNP_GET_DERIVED_KEY likely wants to have a
> > trusted-keys frontend and not isolated behind a vendor-specific ioctl
> > interface.
> 
> TEE's and TPM's are not the exact same thing. Are we sure that any
> future ARM SMC like TEE interface what you say will hold?

Agree, they are not the same thing, I assume that's why trusted-keys has
a TEE and a TPM backend. Also that's the point of common interface
proposals for the per vendor experts to take a look and make sure it
fits their needs. If you have contacts there, please highlight this
thread to them.

> Why do we need a new key type, when we have already trusted keys?

As I mentioned to James to the comment from him about vTPM, if that ends
up just looking like a standard TPM to Linux then nothing new is needed.

> This whole territory should be better defined so that everything
> will fit together.

Yes, the per-vendor differentiation in this space is an impediment to
kernel interface design.

> > This facility is different, it is just aiming to unify this attestation
> > report flow. It scales to any driver that can provide the ->auth_new()
> > operation. I have the sev-guest conversion in this set, and Sathya has
> > tested this with tdx-guest. I am hoping Samuel can evaluate it for
> > cove-guest or whatever that driver ends up being called.
> 
> What about SGX without TDX?

My hope would be that anything that can not be fronted by TPM2_Quote
directly can by frontend by this "TSM" class device (as I will be
switching from Keyring to sysfs).