[tpm2] Re: CMP error: cannot duplicate context:2306 tpm:warn(2.0): out of memory for object contexts

> From: Petr Gotthard <petr.gotthard(a)centrum.cz>
> Sent: Friday, October 8, 2021 11:44 AM
> To: Roberts, William C <william.c.roberts(a)intel.com>; Chris Newman <chris(a)mode51.software>; tpm2(a)lists.01.org <tpm2(a)lists.01.org>
> Subject: Re: [tpm2] Re: CMP error: cannot duplicate context:2306 tpm:warn(2.0): out of memory for object contexts 
 
> Bill,
> we solved this particular issue, but I expect more resource-related troubles are yet to come.

Oh, how exciting :-p
 
> Example 1: OpenSSL often duplicates hash sequences: To hash sequences A,B,C1 and then A,B,C2 they first hash A,B, then duplicate/fork the hash sequence and then complete the hash first for C1 and then for C2. This is a great performance optimization, but when too many dup (forks) are made, the TPM runs out of objects.
 
Why are we doing hashing with the TPM? If we're in an OpenSSL provider cant we just use software provided hashing routines? I see hashing is configurable, but I would imagine off be default is what you want. Do we use validation tickets or anything like that or just the resulting digest? If all we use are the digests, I would make TPM not hash and make that option a nop.

> Example 2: The CMP key update needs 4 objects to operate (old client key, new client key, server key and hash sequence), but the kernel RM (tpm_space.context_tbl) allows only 3 objects. (If I am right.)
 
It does seem that way, but TPM commands only ever need 3 objects alive at once, so that's likely why that was chosen.

https://github.com/torvalds/linux/commit/6c4e79d99e6f42b79040f1a33cd4018f5425030b#diff-7c47a49cbd705c6edb19c967c22c296f00d2391a3483ba849097e908c6513585

Does CMP key really need all 4 of those things in the TPM at once, because currently today that's not actually happening as abrmd is just swapping them in and out.
Also, doesn't CMP use public objects (x509 certs) for some of it?

Looking at the code here:
  - https://github.com/tpm2-software/tpm2-openssl/blob/34c62521a359455b6c4c2bdf6b4e5e149b1a39ba/test/rsa_genpkey_x509_cmp.sh#L41

Are public key operations implemented in software? In tpm2-pkcs11 we implement them in software and hash in software and I have yet to have someone hit a limit but perhaps they are all using abrmd but I thought some were using in-kernel RM.

> In general, the OpenSSL code often pre-loads or caches objects, which will be used later, which causes troubles with the space-constrained TPM. I was not sure whether the tpm2-openssl provider should act as another level of a resource manager and swap the objects to simulate more space than available on the TPM hardware, or whether this is something the resource manager could/should do.

It's something the RM should do, but the in-kernel RM will always be tightly constrained by the amount of kernel memory space it can swap to. I wonder if we could give it a real swap space :-p

> It's definitely a nice problem to think about and most likely something which will need to be addressed in the tpm2-openssl 2.0
 
 
Petr

______________________________________________________________
> Od: "Roberts, William C" <william.c.roberts(a)intel.com>
> Komu: "Chris Newman" <chris(a)mode51.software>, "tpm2(a)lists.01.org" <tpm2(a)lists.01.org>, "Petr Gotthard" <petr.gotthard(a)centrum.cz>
> Datum: 08.10.2021 17:46
> Předmět: [tpm2] Re: CMP error: cannot duplicate context:2306 tpm:warn(2.0): out of memory for object contexts
>
Thats:
tpm2_rc_decode 0x00000902
tpm:warn(2.0): out of memory for object contexts
Are you running against a resource manager? You should probably either use /dev/tpmrm0 or tpm2-abrmd.
You can set the TCTI via the TPM2OPENSSL_TCTI which AFAICT takes strings like tpm2-tools, so something like:
"device:/dev/tpmrm0" or "abrmd".

This also might be a bug, the provider is pretty new. Petr any other ideas I am missing?

Bill


From: Chris Newman <chris(a)mode51.software>
Sent: Sunday, October 3, 2021 6:40 PM
To: tpm2(a)lists.01.org <tpm2(a)lists.01.org>
Subject: [tpm2] CMP error: cannot duplicate context:2306 tpm:warn(2.0): out of memory for object contexts 
 
Hi,
I create an EK and AK using tpm2_createek, tpm2_createak and tpm2_evictcontrol to persist the AK in 0x81010002. The I use the following command with DigiCert's CMPv2 server:
openssl cmp -config /opt/sdk/openssl/current/ssl/openssl.cnf -provider tpm2 -provider default -propquery ?provider=tpm2,tpm2.digest!=yes -cmd ir -server https://demo.one.digicert.com/iot/api/v1/cmp/IOT_1234 -ref 1234 -secret pass:1234 -recipient "/CN=mode51.software" -key handle:0x81010002 -subject "/CN=TestTest" -cacertsout ./capubs.pem -certout ./cl_cert.pem -tls_used -verbosity 8
I get the following error:
DIGEST NEW
DIGEST INIT
DIGEST UPDATE
DIGEST DUP
DIGEST FINAL
DIGEST FREE
DIGEST NEW
DIGEST INIT
DIGEST UPDATE
DIGEST NEW
DIGEST INIT
DIGEST UPDATE
DIGEST DUP
WARNING:esys:src/tss2-esys/api/Esys_ContextLoad.c:279:Esys_ContextLoad_Finish() Received TPM Error
ERROR:esys:src/tss2-esys/api/Esys_ContextLoad.c:93:Esys_ContextLoad() Esys Finish ErrorCode (0x00000902)
DIGEST FREE
DIGEST FREE
DIGEST FREE
CMP DEBUG: disconnected from CMP server
CMP error: cannot duplicate context:2306 tpm:warn(2.0): out of memory for object contexts
CMP error: not able to copy ctx
CMP error: internal error
CMP error: error sending
CMP error: shutdown while in init
CMP error: transfer error:request sent: IR, expected response: IP
RSA FREE
RAND FREE
RAND FREE
RAND FREE
PROVIDER TEARDOWN
 
I've tried tpm2_flushcontext -t.
I recompiled tpm2-openssl with the following option and that appears to have worked around the issue:
--disable-op-digest
Is this what "?provider=tpm2,tpm2.digest!=yes" should effectively do?
 
-- 

Chris Newman 
https://mode51.software 
@mode51software