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

James Bottomley
2024-09-12T14:13:22Z

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.

James