Re: [regression] significant delays when secureboot is enabled since 6.10

Roberto Sassu
2024-09-12T14:52:58Z

On Thu, 2024-09-12 at 10:13 -0400, James Bottomley wrote:
> On Thu, 2024-09-12 at 15:36 +0200, Roberto Sassu wrote:
> > On Thu, 2024-09-12 at 09:26 -0400, James Bottomley wrote:
> > > On Thu, 2024-09-12 at 16:16 +0300, Jarkko Sakkinen wrote:
> > > > On Wed Sep 11, 2024 at 3:21 PM EEST, James Bottomley wrote:
> > > > > On Wed, 2024-09-11 at 10:53 +0200, Roberto Sassu wrote:
> > > [...]
> > > > > > I made few measurements. I have a Fedora 38 VM with TPM
> > > > > > passthrough.
> > > > > >
> > > > > > Kernels: 6.11-rc2+ (guest), 6.5.0-45-generic (host)
> > > > > >
> > > > > > QEMU:
> > > > > >
> > > > > > rc  qemu-kvm                                          1:4.2-
> > > > > > 3ubuntu6.27
> > > > > > ii  qemu-system-x86
> > > > > > 1:6.2+dfsg-
> > > > > > 2ubuntu6.22
> > > > > >
> > > > > >
> > > > > > TPM2_PT_MANUFACTURER:
> > > > > >   raw: 0x49465800
> > > > > >   value: "IFX"
> > > > > > TPM2_PT_VENDOR_STRING_1:
> > > > > >   raw: 0x534C4239
> > > > > >   value: "SLB9"
> > > > > > TPM2_PT_VENDOR_STRING_2:
> > > > > >   raw: 0x36373000
> > > > > >   value: "670"
> > > > > >
> > > > > >
> > > > > > No HMAC:
> > > > > >
> > > > > > # tracer: function_graph
> > > > > > #
> > > > > > # CPU  DURATION                  FUNCTION CALLS
> > > > > > # |     |   |                     |   |   |   |
> > > > > >  0)               |  tpm2_pcr_extend() {
> > > > > >  0)   1.112 us    |    tpm_buf_append_hmac_session();
> > > > > >  0) # 6360.029 us |    tpm_transmit_cmd();
> > > > > >  0) # 6415.012 us |  }
> > > > > >
> > > > > >
> > > > > > HMAC:
> > > > > >
> > > > > > # tracer: function_graph
> > > > > > #
> > > > > > # CPU  DURATION                  FUNCTION CALLS
> > > > > > # |     |   |                     |   |   |   |
> > > > > >  1)               |  tpm2_pcr_extend() {
> > > > > >  1)               |    tpm2_start_auth_session() {
> > > > > >  1) * 36976.99 us |      tpm_transmit_cmd();
> > > > > >  1) * 84746.51 us |      tpm_transmit_cmd();
> > > > > >  1) # 3195.083 us |      tpm_transmit_cmd();
> > > > > >  1) @ 126795.1 us |    }
> > > > > >  1)   2.254 us    |    tpm_buf_append_hmac_session();
> > > > > >  1)   3.546 us    |    tpm_buf_fill_hmac_session();
> > > > > >  1) * 24356.46 us |    tpm_transmit_cmd();
> > > > > >  1)   3.496 us    |    tpm_buf_check_hmac_response();
> > > > > >  1) @ 151171.0 us |  }
> > > > >
> > > > > Well, unfortunately, that tells us that it's the TPM itself
> > > > > that's
> > > > > taking the time processing the security overhead.  The ordering
> > > > > of
> > > > > the commands in tpm2_start_auth_session() shows
> > > > >
> > > > >  37ms for context restore of null key
> > > > >  85ms for start session with encrypted salt
> > > > >   3ms to flush null key
> > > > > -----
> > > > > 125ms
> > > > >
> > > > > If we context save the session, we'd likely only bear a single
> > > > > 37ms
> > > > > cost to restore it (replacing the total 125ms).  However,
> > > > > there's
> > > > > nothing we can do about the extend execution going from 6ms to
> > > > > 24ms, so I could halve your current boot time with security
> > > > > enabled
> > > > > (it's currently 149ms, it would go to 61ms, but it's still 10x
> > > > > slower than the unsecured extend at 6ms)
> > > > >
> > > > > James
> > > >
> > > > I'll hold for better benchmarks.
> > >
> > > Well, yes, I'd like to see this for a variety of TPMs.
> > >
> > > This one clearly shows it's the real time wait for the TPM (since
> > > it dwarfs the CPU time calculation there's not much optimization we
> > > can do on the kernel end).  The one thing that's missing in all of
> > > this is what was the TPM?  but even if it's an outlier that's
> > > really bad at crypto what should we do?  We could have a blacklist
> > > that turns off the extend hmac (or a whitelist that turns it on),
> > > but we can't simply say too bad you need a better TPM.
> >
> > Ops, sorry. I pasted the TPM properties. Was not that clear:
> >
> > Infineon Optiga SLB9670 (interpreting the properties).
>
> OK, that's reasonably modern and common:
>
> https://www.infineon.com/cms/en/product/security-smart-card-solutions/optiga-embedded-security-solutions/optiga-tpm/
>
> I assume it's one of the Q20 (otherwise it would be a TPM 1.2) but what
> firmware version (as in could it be upgraded and the tests re-run to
> see if that makes a difference).
>
> I also need the IMA community to start thinking about what they're
> willing to accept in terms of performance for the added security hmac
> brings to TPM extends.

Just for curiosity, I made a comparison of the boot time of Fedora 38
(minimal installation) without and with HMAC enabled, without and with
the Integrity Digest Cache [1], which I originally designed exactly for
this purpose (one measurement per package):

Without HMAC:
Without Integrity Digest Cache:

[root@fedora ~]# systemd-analyze
Startup finished in 2.486s (kernel) + 3.594s (initrd) + 11.613s (userspace) = 17.694s
multi-user.target reached after 11.559s in userspace.
[root@fedora ~]# cat /sys/kernel/security/ima/ascii_runtime_measurements|wc -l
444

With Integrity Digest Cache:

[root@fedora ~]# systemd-analyze
Startup finished in 2.381s (kernel) + 3.469s (initrd) + 11.794s (userspace) = 17.644s
multi-user.target reached after 11.750s in userspace.
[root@fedora ~]# cat /sys/kernel/security/ima/ascii_runtime_measurements|wc -l
218

With HMAC:
Without Integrity Digest Cache:

[root@fedora ~]# systemd-analyze
Startup finished in 2.911s (kernel) + 3.453s (initrd) + 1min 5.754s (userspace) = 1min 12.119s
multi-user.target reached after 1min 5.707s in userspace.
[root@fedora ~]# cat /sys/kernel/security/ima/ascii_runtime_measurements|wc -l
444

With Integrity Digest Cache:

[root@fedora ~]# systemd-analyze
Startup finished in 2.990s (kernel) + 3.462s (initrd) + 37.038s (userspace) = 43.491s
multi-user.target reached after 36.997s in userspace.
[root@fedora ~]# cat /sys/kernel/security/ima/ascii_runtime_measurements|wc -l
218

[1]: https://lore.kernel.org/linux-integrity/20240905150543.3766895-1-roberto.sassu@huaweicloud.com/

Roberto