Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

Mimi Zohar
2020-07-08T16:13:22Z

Hi Sasha,

On Wed, 2020-07-08 at 11:40 -0400, Sasha Levin wrote:
> From: Maurizio Drocco <maurizio.drocco@ibm.com>
>
> [ Upstream commit 20c59ce010f84300f6c655d32db2610d3433f85c ]
>
> Registers 8-9 are used to store measurements of the kernel and its
> command line (e.g., grub2 bootloader with tpm module enabled). IMA
> should include them in the boot aggregate. Registers 8-9 should be
> only included in non-SHA1 digests to avoid ambiguity.

Prior to Linux 5.8, the SHA1 template data hashes were padded before
being extended into the TPM.  Support for calculating and extending
the per TPM bank template data digests is only being upstreamed in
Linux 5.8.

How will attestation servers know whether to include PCRs 8 & 9 in the
the boot_aggregate calculation?  Now, there is a direct relationship
between the template data SHA1 padded digest not including PCRs 8 & 9,
and the new per TPM bank template data digest including them.

Mimi