From: Mimi Zohar <zohar@linux.ibm.com>
To: Tyler Hicks <tyhicks@linux.microsoft.com>,
Jerry Snitselaar <jsnitsel@redhat.com>
Cc: Sasha Levin <sashal@kernel.org>,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
Maurizio Drocco <maurizio.drocco@ibm.com>,
Bruno Meneguele <bmeneg@redhat.com>,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org
Subject: Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements
Date: Tue, 12 Jan 2021 11:56:45 -0500 [thread overview]
Message-ID: <3a163a1839ff469acfa8dbb889c1b0889ec771bc.camel@linux.ibm.com> (raw)
In-Reply-To: <20210112153534.GA4146@sequoia>
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 <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.
> > > > > >
> > > > > > 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
next prev parent reply other threads:[~2021-01-12 16:58 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-08 15:40 [PATCH AUTOSEL 5.7 01/30] drm/msm: fix potential memleak in error branch Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 02/30] drm/msm/dpu: allow initialization of encoder locks during encoder init Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements Sasha Levin
2020-07-08 16:13 ` Mimi Zohar
2020-07-09 1:27 ` Sasha Levin
2020-11-29 13:17 ` Mimi Zohar
2020-12-01 0:21 ` Sasha Levin
2020-12-01 3:13 ` Mimi Zohar
2020-12-02 23:53 ` Sasha Levin
2020-12-11 3:10 ` Tyler Hicks
2020-12-11 11:01 ` Mimi Zohar
2020-12-11 17:46 ` James Bottomley
2020-12-13 2:22 ` Mimi Zohar
2020-12-28 19:28 ` Ken Goldman
2020-12-29 2:01 ` Mimi Zohar
2020-12-14 16:42 ` Tyler Hicks
2021-01-12 15:35 ` Tyler Hicks
2021-01-12 16:56 ` Mimi Zohar [this message]
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 04/30] drm/exynos: Properly propagate return value in drm_iommu_attach_device() Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 05/30] drm/exynos: fix ref count leak in mic_pre_enable Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 06/30] x86/fpu: Reset MXCSR to default in kernel_fpu_begin() Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 07/30] exfat: Set the unused characters of FileName field to the value 0000h Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 08/30] exfat: call sync_filesystem for read-only remount Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 09/30] thermal/drivers: imx: Fix missing of_node_put() at probe time Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 10/30] ACPI: DPTF: Add battery participant for TigerLake Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 11/30] blk-mq-debugfs: update blk_queue_flag_name[] accordingly for new flags Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 12/30] m68k: nommu: register start of the memory with memblock Sasha Levin
2020-07-08 15:40 ` [PATCH AUTOSEL 5.7 13/30] m68k: mm: fix node memblock init Sasha Levin
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