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Tue, 12 Jan 2021 16:56:49 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D1A1E4C04E; Tue, 12 Jan 2021 16:56:46 +0000 (GMT) Received: from sig-9-65-221-171.ibm.com (unknown [9.65.221.171]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 12 Jan 2021 16:56:46 +0000 (GMT) Message-ID: <3a163a1839ff469acfa8dbb889c1b0889ec771bc.camel@linux.ibm.com> Subject: Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements From: Mimi Zohar To: Tyler Hicks , Jerry Snitselaar Cc: Sasha Levin , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Maurizio Drocco , Bruno Meneguele , linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org Date: Tue, 12 Jan 2021 11:56:45 -0500 In-Reply-To: <20210112153534.GA4146@sequoia> References: <20200708154116.3199728-1-sashal@kernel.org> <20200708154116.3199728-3-sashal@kernel.org> <1594224793.23056.251.camel@linux.ibm.com> <20200709012735.GX2722994@sasha-vm> <5b8dcdaf66fbe2a39631833b03772a11613fbbbf.camel@linux.ibm.com> <20201211031008.GN489768@sequoia> <659c09673affe9637a5d1391c12af3aa710ba78a.camel@linux.ibm.com> <20201214164222.GK4951@sequoia> <20210112153534.GA4146@sequoia> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.28.5 (3.28.5-14.el8) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343,18.0.737 definitions=2021-01-12_12:2021-01-12,2021-01-12 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 clxscore=1031 malwarescore=0 lowpriorityscore=0 mlxlogscore=999 phishscore=0 suspectscore=0 priorityscore=1501 spamscore=0 impostorscore=0 mlxscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2101120095 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Tyler, On Tue, 2021-01-12 at 09:35 -0600, Tyler Hicks wrote: > On 2020-12-14 10:42:24, Tyler Hicks wrote: > > On 2020-12-11 06:01:54, Mimi Zohar wrote: > > > On Thu, 2020-12-10 at 21:10 -0600, Tyler Hicks wrote: > > > > On 2020-11-29 08:17:38, 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 > > > > > > >> > > > > > > >> [ 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. > > > > > > > > I'm still not clear on how an attestation server would know to include > > > > PCRs 8 and 9 after this change came through a stable kernel update. It > > > > doesn't seem like something appropriate for stable since it requires > > > > code changes to attestation servers to handle the change. > > > > > > > > I know this has already been released in some stable releases, so I'm > > > > too late, but perhaps I'm missing something. > > > > > > The point of adding PCRs 8 & 9 only to non-SHA1 boot_aggregate values > > > was to avoid affecting existing attestation servers. The intention was > > > when attestation servers added support for the non-sha1 boot_aggregate > > > values, they'd also include PCRs 8 & 9. The existing SHA1 > > > boot_aggregate value remains PCRs 0 - 7. > > > > AFAIK, there's nothing that prevents the non-SHA1 TPM 2.0 PCR banks from > > being used even before v5.8, albeit with zero padded SHA1 digests. > > Existing attestation servers that already support that configuration are > > broken by this stable backport. > To wrap up this thread, I think the last thing to address is if this > commit should be reverted from stable kernels? Do you have any thoughts > about that, Mimi? > > > > > > To prevent this or something similar from happening again, what should > > > have been the proper way of including PCRs 8 & 9? > > > > I don't think that commits like 6f1a1d103b48 ("ima: Switch to > > ima_hash_algo for boot aggregate") and 20c59ce010f8 ("ima: extend > > boot_aggregate with kernel measurements") should be backported to > > stable. > > > > Including PCRs 8 and 9 definitely makes sense to include in the > > boot_aggregate value but limiting such a change to "starting in 5.8", > > rather than "starting in 5.8 and 5.4.82", is the safer approach when > > attestation server modifications are required. As I recall, commit 6f1a1d103b48 ("ima: Switch to ima_hash_algo for boot aggregate") was backported to address TPMs without SHA1 support, as reported by Jerry. Mimi