[PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Sasha Levin]

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.

Signed-off-by: Maurizio Drocco <maurizio.drocco@ibm.com>
Reviewed-by: Bruno Meneguele <bmeneg@redhat.com>
Tested-by: Bruno Meneguele <bmeneg@redhat.com>  (TPM 1.2, TPM 2.0)
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 security/integrity/ima/ima.h        |  2 +-
 security/integrity/ima/ima_crypto.c | 15 ++++++++++++++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 495e28bd488e6..844a55225ede0 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -30,7 +30,7 @@
 
 enum ima_show_type { IMA_SHOW_BINARY, IMA_SHOW_BINARY_NO_FIELD_LEN,
 		     IMA_SHOW_BINARY_OLD_STRING_FMT, IMA_SHOW_ASCII };
-enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8 };
+enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 };
 
 /* digest size for IMA, fits SHA1 or MD5 */
 #define IMA_DIGEST_SIZE		SHA1_DIGEST_SIZE
diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index fb27174806ba4..e0738d1d143d7 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -682,13 +682,26 @@ static int ima_calc_boot_aggregate_tfm(char *digest, u16 alg_id,
 	if (rc != 0)
 		return rc;
 
-	/* cumulative sha1 over tpm registers 0-7 */
+	/* cumulative digest over TPM registers 0-7 */
 	for (i = TPM_PCR0; i < TPM_PCR8; i++) {
 		ima_pcrread(i, &d);
 		/* now accumulate with current aggregate */
 		rc = crypto_shash_update(shash, d.digest,
 					 crypto_shash_digestsize(tfm));
 	}
+	/*
+	 * Extend cumulative digest over TPM registers 8-9, which contain
+	 * measurement for the kernel command line (reg. 8) and image (reg. 9)
+	 * in a typical PCR allocation. Registers 8-9 are only included in
+	 * non-SHA1 boot_aggregate digests to avoid ambiguity.
+	 */
+	if (alg_id != TPM_ALG_SHA1) {
+		for (i = TPM_PCR8; i < TPM_PCR10; i++) {
+			ima_pcrread(i, &d);
+			rc = crypto_shash_update(shash, d.digest,
+						crypto_shash_digestsize(tfm));
+		}
+	}
 	if (!rc)
 		crypto_shash_final(shash, digest);
 	return rc;
-- 
2.25.1

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Mimi Zohar]

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.

Mimi

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Sasha Levin]

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!

-- 
Thanks,
Sasha

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Mimi Zohar]

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.

Any place commit 6f1a1d103b48 was backported [2], this commit
20c59ce010f8 ("ima: extend boot_aggregate with kernel measurements")
should be backported as well.

thanks,

Mimi

[1] commit 1ea973df6e21 ("ima: Calculate and extend PCR with digests in ima_template_entry")
[2] commit 6f1a1d103b48 ("ima: Switch to ima_hash_algo for boot aggregate")

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Sasha Levin]

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@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.
>
>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

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Mimi Zohar]

On Mon, 2020-11-30 at 19:21 -0500, Sasha Levin wrote:
> 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@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.
> >
> >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.

For 5.4, both "git cherry-pick" and "git am --3way" for 20c59ce010f8
seem to work.

thanks,

Mimi

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Sasha Levin]

On Mon, Nov 30, 2020 at 10:13:02PM -0500, Mimi Zohar wrote:
>On Mon, 2020-11-30 at 19:21 -0500, Sasha Levin wrote:
>> 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@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.
>> >
>> >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.
>
>For 5.4, both "git cherry-pick" and "git am --3way" for 20c59ce010f8
>seem to work.

You're right, I've grabbed it too. Thanks!

-- 
Thanks,
Sasha

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Tyler Hicks]

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.

Tyler

> 
> Any place commit 6f1a1d103b48 was backported [2], this commit
> 20c59ce010f8 ("ima: extend boot_aggregate with kernel measurements")
> should be backported as well.
> 
> thanks,
> 
> Mimi
> 
> [1] commit 1ea973df6e21 ("ima: Calculate and extend PCR with digests in ima_template_entry")
> [2] commit 6f1a1d103b48 ("ima: Switch to ima_hash_algo for boot aggregate")
> 

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Mimi Zohar]

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.

To prevent this or something similar from happening again, what should
have been the proper way of including PCRs 8 & 9?

thanks,

Mimi

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[James Bottomley]

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 <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.
> 
> 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).

James

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Mimi Zohar]

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 <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.
> > 
> > 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

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Tyler Hicks]

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 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.

Tyler

> 
> thanks,
> 
> Mimi
> 

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Ken Goldman]

On 12/12/2020 9:22 PM, Mimi Zohar wrote:
> Ok.   Going forward, it sounds like we need to define a new
> "boot_aggregate" record.  One that contains a version number and PCR
> mask.

Just BTW, there is a TCG standard for a TPM 2.0 PCR mask that works
well.

There is also a standard for an event log version number.  It is
the first event of a TPM 2.0 event log.  It is strange.

One useful field, though, is a mapping between the algorithm ID (e.g.,
sha256 is 0x000b) and the digest size (e.g., 32 bytes).  This permits
a parser to parse a log even when it encounters an unknown digest
algorithm.

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Mimi Zohar]

On Mon, 2020-12-28 at 14:28 -0500, Ken Goldman wrote:
> On 12/12/2020 9:22 PM, Mimi Zohar wrote:
> > Ok.   Going forward, it sounds like we need to define a new
> > "boot_aggregate" record.  One that contains a version number and PCR
> > mask.
> 
> Just BTW, there is a TCG standard for a TPM 2.0 PCR mask that works
> well.

Sounds good.
> 
> There is also a standard for an event log version number.  It is
> the first event of a TPM 2.0 event log.  It is strange.

Ok
> 
> One useful field, though, is a mapping between the algorithm ID (e.g.,
> sha256 is 0x000b) and the digest size (e.g., 32 bytes).  This permits
> a parser to parse a log even when it encounters an unknown digest
> algorithm.

The template data is prefixed with the template data length.  The
problem is verifying the boot_aggregate, not parsing the log.

thanks,

Mimi

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Tyler Hicks]

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?

Tyler

> 
> > 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.
> 
> Tyler
> 
> > 
> > thanks,
> > 
> > Mimi
> > 

Re: [PATCH AUTOSEL 5.7 03/30] ima: extend boot_aggregate with kernel measurements

[Mimi Zohar]

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