linux-kernel - Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot

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Message-ID: <20201201002157.GT643756@sasha-vm>
Date:   Mon, 30 Nov 2020 19:21:57 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Maurizio Drocco <maurizio.drocco@....com>,
        Bruno Meneguele <bmeneg@...hat.com>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel
 measurements

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@....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.
>>
>> 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