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

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Date:   Tue, 8 Aug 2023 23:32:10 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "dionnaglaze@...gle.com" <dionnaglaze@...gle.com>
CC:     "sameo@...osinc.com" <sameo@...osinc.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "James.Bottomley@...senpartnership.com" 
        <James.Bottomley@...senpartnership.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>
Subject: Re: [PATCH 0/4] keys: Introduce a keys frontend for attestation
 reports

On Tue, 2023-08-08 at 11:17 -0700, Dan Williams wrote:
> Dionna Amalie Glaze wrote:
> > > 
> > > I do not see sysfs precluding a use case like that. If the kernel can
> > > call out to userspace for TLS connection setup [1], then advanced user
> > > can call out to a daemon for workload provenance setup. Recall that TDX
> > > will round trip through the quoting enclave for these reports and,
> > > without measuring, that seems to have the potential to dominate the
> > > setup time vs the communication to ask a daemon to convey a report.
> > > 
> > 
> > It's rather hard to get new daemons approved for container
> > distributions since they end up as resource hogs.
> > I really don't think it's appropriate to delegate to a daemon to
> > single-thread use of a kernel interface when the interface could
> > provide functional semantics to begin with.
> 
> That's fair, it's also not without precedence for the kernel to await a
> strong motivation of a use case before taking on a higher maintenance
> burden. Unifying kernel interfaces is important for maintainability and
> difficult / needs care. sysfs simplifies maintainability (but exports
> complexity to userspace), keyring simplifies that (but there is a valid
> argument that this is not a key), ioctl complicates that (it is not as
> amenable to transport unification as the above options).
> 

I don't quite follow why ioctl() is not amenable to transport unification as the
/sysfs?  IIUC both are new ABI(s) to the userspace thus userspace needs to adopt
anyway.  

On the other hand, ioctl() seems to be able to handle concurrent requests better
than /sysfs, if we want to support the case that integrating attestation to the
handshake protocols.