On Sun, Nov 29, 2020 at 08:17:38AM -0500, Mimi Zohar wrote:
Hi Sasha,
On Wed, 2020-07-08 at 21:27 -0400, Sasha Levin wrote:
On Wed, Jul 08, 2020 at 12:13:13PM -0400, Mimi Zohar wrote:
>Hi Sasha,
>
>On Wed, 2020-07-08 at 11:40 -0400, Sasha Levin wrote:
>> From: Maurizio Drocco <maurizio.drocco@xxxxxxx>
>>
>> [ 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.
Got it, I'll drop it then, thank you!
After re-thinking this over, I realized that the attestation server can
verify the "boot_aggregate" based on the quoted PCRs without knowing
whether padded SHA1 hashes or per TPM bank hash values were extended
into the TPM[1], but non-SHA1 boot aggregate values [2] should always
include PCRs 8 & 9.
Any place commit 6f1a1d103b48 was backported [2], this commit
20c59ce010f8 ("ima: extend boot_aggregate with kernel measurements")
should be backported as well.
Which kernels should it apply to? 5.7 is EOL now, so I looked at 5.4 but
it doesn't apply cleanly there.
--
Thanks,
Sasha
