Re: [PATCH v7 12/21] tpm: Add NULL primary creation

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Sat Mar 30, 2024 at 8:48 PM EET, Gabríel Arthúr Pétursson wrote:
> On Tue, 2024-02-13 at 12:13 -0500, James Bottomley wrote:
> > +	/* unique: key specific; for ECC it is two points */
> > +	tpm_buf_append_u16(&template, 0);
> > +	tpm_buf_append_u16(&template, 0);
>
> Shouldn't the points be 32 bytes each in size, filled with zeros?
>
> The TCP TPM 2.0 Provisioning Guidance defines the SRK Template as a
> diff on top of Template L-2 (for ECC keys) as defined in the EK
> Credential Profile 2.0 document.
>
> Template L-2 calls for the X and Y points to be of 32 bytes each,
> filled with zeros. The Provisioning Guidance does not call for zero-
> sized points.
>
> For example, let's create an ECC Endorsement Key using the standard
> template then print its name:
>
>    tpm2_createek -G ecc -c /dev/null -u ./ek.pub
>    tpm2_loadexternal -c n -u ./ek.pub
>
> Equivalently using tpm2_createprimary:
>
>    perl -e 'print "\0"x64' | tpm2_createprimary -C e -o ./ek.pub -G ecc -a 'fixedtpm|fixedparent|sensitivedataorigin|adminwithpolicy|restricted|decrypt' -L 837197674484b3f81a90cc8d46a5d724fd52d76e06520b64f2a1da1b331469aa -u -
>    tpm2_loadexternal -c n -u ./ek.pub
>
> You'll find that the key's public modulus matches that of the EK
> Certificate imprinted by the manufacturer, indicating we got the
> template correct.
>
> To generate a standard SRK key, the TCG TPM2 Provisioning Guidance
> states we should:
>
> 	1. set userWithAuth,
> 	2. clear adminWithPolicy
> 	3. set noDA, and
> 	4. clear the authorization policy.
>
> There's no mention of alterations to the unique field.
>
> Let's also create the key in the null hierarchy:
>
>    perl -e 'print "\0"x64' | tpm2_createprimary -C n -o ./null.pub -G ecc -a 'fixedtpm|fixedparent|sensitivedataorigin|userwithauth|noda|restricted|decrypt' -u -
>    tpm2_loadexternal -c n -u ./null.pub
>
> The name does not match the kernel's name for the null key.

Null key is not provisioned, what is the motivation here?

Not saying no, just asking for details...

There's couple of things that lack in this patch set ATM:

1. Neither kselftest additions nor not even proper testing
   instructions. Why 21 patches and zero tests? How one should
   decide when the work is "complete"?
2. I still don't know what version of QEMU I should patch to
   test corner cases from an URL, which I cannot recall :-)
   Highlights the first issue.

So for the time being the patch set is NAK just because we lack
clear definition of done here. I revisit it only when I know how
to test it.

BR, Jarkko