linux-kernel - Re: One question about trusted key of keyring in Linux kernel.

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Message-ID: <1574877977.3551.5.camel@linux.ibm.com>
Date:   Wed, 27 Nov 2019 10:06:17 -0800
From:   James Bottomley <jejb@...ux.ibm.com>
To:     "Zhao, Shirley" <shirley.zhao@...el.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>
Cc:     "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "'Mauro Carvalho Chehab'" <mchehab+samsung@...nel.org>,
        "Zhu, Bing" <bing.zhu@...el.com>,
        "Chen, Luhai" <luhai.chen@...el.com>
Subject: Re: One question about trusted key of keyring in Linux kernel.

On Tue, 2019-11-26 at 07:32 +0000, Zhao, Shirley wrote:
> Thanks for your feedback, Mimi. 
> But the document of dracut can't solve my problem. 
> 
> I did more test these days and try to descript my question in more
> detail. 
> 
> In my scenario, the trusted key will be sealed into TPM with PCR
> policy. 
> And there are some related options in manual like 
>        hash=         hash algorithm name as a string. For TPM 1.x the
> only
>                      allowed value is sha1. For TPM 2.x the allowed
> values
>                      are sha1, sha256, sha384, sha512 and sm3-256.
>        policydigest= digest for the authorization policy. must be
> calculated
>                      with the same hash algorithm as specified by the
> 'hash='
>                      option.
>        policyhandle= handle to an authorization policy session that
> defines the
>                      same policy and with the same hash algorithm as
> was used to
>                      seal the key. 
> 
> Here is my test step. 
> Firstly, the pcr policy is generated as below: 
> $ tpm2_createpolicy --policy-pcr --pcr-list sha256:7 --policy
> pcr7_bin.policy > pcr7.policy
> 
> Pcr7.policy is the ascii hex of policy:
> $ cat pcr7.policy
> 321fbd28b60fcc23017d501b133bd5dbf2889814588e8a23510fe10105cb2cc9
> 
> Then generate the trusted key and configure policydigest and get the
> key ID: 
> $ keyctl add trusted kmk "new 32 keyhandle=0x81000001 hash=sha256
> policydigest=`cat pcr7.policy`" @u
> 874117045
> 
> Save the trusted key. 
> $ keyctl pipe 874117045 > kmk.blob
> 
> Reboot and load the key. 
> Start a auth session to generate the policy:
> $ tpm2_startauthsession -S session.ctx
> session-handle: 0x3000000
> $ tpm2_pcrlist -L sha256:7 -o pcr7.sha256
> $ tpm2_policypcr -S session.ctx -L sha256:7 -F pcr7.sha256 -f
> pcr7.policy
> policy-digest:
> 0x321FBD28B60FCC23017D501B133BD5DBF2889814588E8A23510FE10105CB2CC9
> 
> Input the policy handle to load trusted key:
> $ keyctl add trusted kmk "load `cat kmk.blob` keyhandle=0x81000001
> policyhandle=0x3000000" @u
> add_key: Operation not permitted
> 
> The error should be policy check failed, because I use TPM command to
> unseal directly with error of policy check failed. 
> $ tpm2_unseal -c 0x81000001 -L sha256:7
> ERROR on line: "81" in file: "./lib/log.h": Tss2_Sys_Unseal(0x99D) -
> tpm:session(1):a policy check failed
> ERROR on line: "213" in file: "tools/tpm2_unseal.c": Unseal failed!
> ERROR on line: "166" in file: "tools/tpm2_tool.c": Unable to run
> tpm2_unseal

I think there's a miscommunication here: you're complaining about the
error returned from a trusted key unseal operation that *should* fail,
correct?  You think it should return a TPM error but instead it returns
-EPERM.  That's completely correct: we translate all TPM errors into
linux ones as we pass them up to userspace, so the best we can do is
operation not permitted.

James