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Sun, 13 Dec 2020 02:22:20 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7803DAE057; Sun, 13 Dec 2020 02:22:18 +0000 (GMT) Received: from li-f45666cc-3089-11b2-a85c-c57d1a57929f.ibm.com (unknown [9.160.98.152]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Sun, 13 Dec 2020 02:22:18 +0000 (GMT) Message-ID: <05266e520f62276b07e76aab177ea6db47916a7f.camel@linux.ibm.com> Subject: Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements From: Mimi Zohar To: James Bottomley , Tyler Hicks 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: Sat, 12 Dec 2020 21:22:17 -0500 In-Reply-To: <76710d8ec58c440ed7a7b446696b8659f694d0db.camel@HansenPartnership.com> 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> <76710d8ec58c440ed7a7b446696b8659f694d0db.camel@HansenPartnership.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.28.5 (3.28.5-12.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=2020-12-12_12:2020-12-11,2020-12-12 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 impostorscore=0 clxscore=1031 bulkscore=0 adultscore=0 lowpriorityscore=0 priorityscore=1501 phishscore=0 mlxlogscore=999 mlxscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012130011 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2020-12-11 at 09:46 -0800, James Bottomley wrote: > On Fri, 2020-12-11 at 06:01 -0500, 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. > > > > To prevent this or something similar from happening again, what > > should have been the proper way of including PCRs 8 & 9? > > Just to be pragmatic: this is going to happen again. Shim is already > measuring the Mok variables through PCR 14, so if we want an accurate > boot aggregate, we're going to have to include PCR 14 as well (or > persuade shim to measure through a PCR we're already including, which > isn't impossible since I think shim should be measuring the Mok > variables using the EV_EFI_VARIABLE_DRIVER_CONFIG event and, since it > affects secure boot policy, that does argue it should be measured > through PCR 7). Ok. Going forward, it sounds like we need to define a new "boot_aggregate" record. One that contains a version number and PCR mask. Mimi