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Date:   Sun, 20 Feb 2022 18:19:59 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        linux-integrity@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, Petr Vorel <pvorel@...e.cz>
Subject: Re: init_ima() adds 8 % to boot time

On Sun, 2022-02-20 at 23:57 +0100, Jarkko Sakkinen wrote:
> On Sun, Feb 20, 2022 at 10:19:37AM -0500, Mimi Zohar wrote:
> > [Cc'ing Jarkko, Petr Vorel]
> > 
> > Hi Paul,
> > 
> > On Sat, 2022-02-19 at 10:44 +0100, Paul Menzel wrote:
> > > Dear Linux folks,
> > > 
> > > 
> > > Debian builds its Linux kernel image with `CONFIG_IMA=y` since version 
> > > 5.13.9 [1]. Unfortunately, on the Dell Latitude E7250 `init_ima` takes 
> > > around 33 ms, adding 8 % to the boot time up to loading the initrd.
> > > 
> > >      [    0.000000] Linux version 5.17.0-rc4-amd64 
> > > (debian-kernel@...ts.debian.org) (gcc-11 (Debian 11.2.0-16) 11.2.0, GNU 
> > > ld (GNU Binutils for Debian) 2.38) #1 SMP PREEMPT Debian 5.17~rc4-1~exp1 
> > > (2022-02-18)
> > >      […]
> > >      [    0.238520] calling  init_tis+0x0/0xde @ 1
> > >      [    0.254749] tpm_tis 00:08: 1.2 TPM (device-id 0x3205, rev-id 80)
> > >      [    0.285665] initcall init_tis+0x0/0xde returned 0 after 46038 usecs
> > >      […]
> > >      [    0.301327] calling  init_ima+0x0/0xb5 @ 1
> > >      [    0.301332] ima: Allocated hash algorithm: sha256
> > >      [    0.335502] ima: No architecture policies found
> > >      [    0.335520] initcall init_ima+0x0/0xb5 returned 0 after 33389 usecs
> > >      […]
> > >      [    0.447312] Run /init as init process
> > > 
> > > Tracing `init_ima` with a depth of 5 shows 
> > > `ima_calc_boot_aggregate_tfm()` takes 24 ms, and 
> > > `ima_add_template_entry()` takes 10 ms.
> > > 
> > >          1.282630 |   1)   swapper-1    |               | 
> > > ima_add_boot_aggregate() {
> > >          1.282631 |   1)   swapper-1    |               | 
> > > ima_calc_boot_agg:0regate() {
> > >          1.282631 |   1)   swapper-1    |   0.153 us    | 
> > > ima_alloc_tfm();
> > >          1.282631 |   1)   swapper-1    | * 24404.59 us | 
> > > ima_calc_boot_aggregate_tfm();
> > >          1.307037 |   1)   swapper-1    |   0.482 us    | 
> > > ima_free_tfm.part.0();
> > >          1.307038 |   1)   swapper-1    | * 24407.06 us |        } /* 
> > > ima_calc_boot_aggregate */
> > >          1.307038 |   1)   swapper-1    |               | 
> > > ima_alloc_init_template() {
> > >          1.307038 |   1)   swapper-1    |   0.173 us    | 
> > > ima_template_desc_current();
> > >          1.307039 |   1)   swapper-1    |   0.836 us    | 
> > > __kmalloc();
> > >          1.307040 |   1)   swapper-1    |   0.580 us    | 
> > > __kmalloc();
> > >          1.307041 |   1)   swapper-1    |   1.555 us    | 
> > > ima_eventdigest_ng_init();
> > >          1.307043 |   1)   swapper-1    |   1.275 us    | 
> > > ima_eventname_ng_init();
> > >          1.307044 |   1)   swapper-1    |   0.256 us    | 
> > > ima_eventsig_init();
> > >          1.307045 |   1)   swapper-1    |   6.618 us    |        } /* 
> > > ima_alloc_init_template */
> > >          1.307045 |   1)   swapper-1    |               | 
> > > ima_store_template() {
> > >          1.307045 |   1)   swapper-1    |   5.049 us    | 
> > > ima_calc_field_array_hash();
> > >          1.307051 |   1)   swapper-1    | # 9316.953 us | 
> > > ima_add_template_entry();
> > >          1.316369 |   1)   swapper-1    | # 9323.728 us |        } /* 
> > > ima_store_template */
> > >          1.316369 |   1)   swapper-1    | * 33738.54 us |      } /* 
> > > ima_add_boot_aggregate */
> > > 
> > > Tracing `ima_calc_boot_aggregate_tfm()` (attached) shows that the first 
> > > `tpm1_pcr_read()` takes 16 ms in `tpm_transmit()`. Is communicating with 
> > > the TPM supposed to be that slow?
> > > 
> > > In the last years, Linux decreased it’s boot time a lot, so do you see a 
> > > way to move things out of the hot path and get `init_ima` well below 10 
> > > ms? (As systems get faster and faster, having systems with standard 
> > > distributions to be up below two seconds after pressing the power button 
> > > should be a reasonable goal (500 ms firmware (like coreboot) + 500 ms 
> > > Linux kernel + 1 s user space).
> > > 
> > > 
> > > [1]: 
> > > https://salsa.debian.org/kernel-team/linux/-/commit/6e679322d7d98d30b4a8a3d1b659c899a6e9d4df
> > 
> > Thank you including the initial and other TPM delays.  The main reason
> > for the "boot_aggregate" is to tie the pre-OS measurements to the post
> > OS measurement list.  Without the TPM based 'boot_aggregate', any IMA
> > measurement list could be used to verify a TPM quote.  The
> > 'boot_aggregate' is calculated, originally, based on PCRs 0 - 7 and
> > more recently may include PCRs 8 & 9 as well.  The 'boot_aggregate' is
> > the first record in the IMA measurement list and the first record after
> > a soft reboot (kexec).  It is the one and only IMA measurement record
> > not dependent on policy.
> > 
> > There are TPM 1.2 & 2.0 standards' requirements, but there are also
> > buggy TPMs which don't adhere to them to such an extent that IMA goes
> > into 'TPM-bypass' mode. Perhaps for those not interested in extending
> > the concepts of trusted boot to the running OS, defining a new boot
> > command line option to force IMA into this 'TPM-bypass' mode would be
> > an acceptable alternative to the delay.  The IMA measurement list would
> > still include a 'boot_aggregate' record, but one containing 0's.
> 
> I support the opt-in boot option.
> 
> If the full hardware specifications are known for a device, you might want
> to use this.

The default would be to extend the TPM with the 'boot_aggregate', with
an option to opt-out of extending the TPM.

-- 
thanks,

Mimi


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