linux-kernel - Re: [GIT PULL] TPM DEVICE DRIVER changes for v5.14

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Date:   Mon, 28 Jun 2021 15:21:18 -0400
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jarkko Sakkinen <jarkko@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        James Morris James Morris <jmorris@...ei.org>,
        David Howells <dhowells@...hat.com>,
        Peter Huewe <peterhuewe@....de>
Subject: Re: [GIT PULL] TPM DEVICE DRIVER changes for v5.14


On 6/28/21 3:11 PM, Linus Torvalds wrote:
> On Mon, Jun 28, 2021 at 11:33 AM Stefan Berger <stefanb@...ux.ibm.com> wrote:
>> The removal is triggered by the user changing the type of key from what
>> is in the keyfile.
>
>
> So no. No backups either. Because there is not a single valid
> situation where you'd want a backup - because the kernel build should
> never EVER modify the original.
>
> Maybe I misunderstand what is going on, but I think the whole thing is
> completely wrongly designed. The _only_ key that the kernel build
> should touchn is the auto-generated throw-away one (ie
> "certs/signing_key.pem"), not CONFIG_MODULE_SIG_KEY in general.

Correct, and the code (certs/Makefile) is surrounded by the check for 
this particular file here, so it won't touch anything else:

[...]

ifeq ($(CONFIG_MODULE_SIG_KEY),"certs/signing_key.pem")

ifeq ($(openssl_available),yes)
X509TEXT=$(shell openssl x509 -in $(CONFIG_MODULE_SIG_KEY) -text)
endif

# Support user changing key type
ifdef CONFIG_MODULE_SIG_KEY_TYPE_ECDSA
keytype_openssl = -newkey ec -pkeyopt ec_paramgen_curve:secp384r1
ifeq ($(openssl_available),yes)
$(if $(findstring id-ecPublicKey,$(X509TEXT)),,$(shell rm -f 
$(CONFIG_MODULE_SIG_KEY)))
endif
endif # CONFIG_MODULE_SIG_KEY_TYPE_ECDSA

ifdef CONFIG_MODULE_SIG_KEY_TYPE_RSA
ifeq ($(openssl_available),yes)
$(if $(findstring rsaEncryption,$(X509TEXT)),,$(shell rm -f 
$(CONFIG_MODULE_SIG_KEY)))
endif
endif # CONFIG_MODULE_SIG_KEY_TYPE_RSA

[...]


There's one dent in this patch series that requires suppressing an error 
output:  https://lkml.org/lkml/2021/6/25/452


   Stefan


>
>                   Linus