Re: [PATCH v2] tpm2_key_protector: dump PCRs on policy fail

[Gary Lin]

On Tue, Dec 17, 2024 at 03:29:02PM +0100, Daniel Kiper wrote:
> On Tue, Dec 17, 2024 at 11:45:32AM +0800, Gary Lin wrote:
> > On Tue, Dec 17, 2024 at 09:35:34AM +0800, Gary Lin wrote:
> > > On Mon, Dec 16, 2024 at 05:28:34PM +0100, Daniel Kiper wrote:
> > > > On Thu, Dec 12, 2024 at 02:11:24PM +0800, Gary Lin wrote:
> > > > > PCR mismatching is one common cause of TPM key unsealing fail. Since 
> > > > > the
> > > > > system may be compromised, it is not safe to boot into OS to get the 
> > > > > PCR
> > > > > values and TPM eventlog for the further investigation.
> > > > >
> > > > > To provide some hints, GRUB now dumps PCRs on policy fail, so the user
> > > > > can check the current PCR values. PCR 0~15 are chosen to cover the
> > > > > firmware, bootloader, and OS.
> > > > >
> > > > > The sample output:
> > > > >
> > > > > PCR Mismatching! Check firmware and bootloader before typing 
> > > > > passphrase!
> > > > > TPM PCR [sha256]:
> > > > >   00: 115c89bfa0e59e050cda5d2664031d225305f3582cf0c2afcb7c1f1ac2a7cf8d
> > > > >   01: 079b3eadca25e10248daea4b1d508e5cfb703db28386be809a0b375c0a0a80a5
> > > > >   02: 2cd8ec3de6a07e1fd39676100db57ba62372e820c19812fee55899f65746e192
> > > > >   03: 9423b585d4eac05c97a0c06bca8898ad0ca519a6b810dcb91129bcdc10f4b112
> > > > >   04: fa36bf5c9110d3891f040e2146d157484cd41123fa8faf4bc6b91db3d12b70ca
> > > > >   05: 13e9ea9e38e5258e6ee2b6ae94a3cece0137490ef95c65caaac10cdf5e1bc40d
> > > > >   06: 3ac10d749054a818806788f4e4eaa2fb4dd7d13ce0e99dc175145b63c34bb71c
> > > > >   07: a6657a60f77928cad614a7ad153ab9ae0bed48e33b70348ae11a26762002b3bc
> > > > >   08: 42e04f5bac1965535cb6bdb30c62bb199b1ba21d1ec6b22d0da159dfc925b8bb
> > > > >   09: 5c83e8be79d4a432e6d409610de389ee6f1ac0c193f38d84a9ff94f360bd458b
> > > > >   10: 0000000000000000000000000000000000000000000000000000000000000000
> > > > >   11: 0000000000000000000000000000000000000000000000000000000000000000
> > > > >   12: 0000000000000000000000000000000000000000000000000000000000000000
> > > > >   13: 0000000000000000000000000000000000000000000000000000000000000000
> > > > >   14: 894dd8e4ca1bb62e055f674f9390a39c4643ebdd1014702feef000c47e36a003
> > > > >   15: 0000000000000000000000000000000000000000000000000000000000000000
> > > > > error: failed to unseal sealed key (TPM2_Unseal: 0x99d).
> > > > > error: no key protector provided a usable key for luks 
> > > > > (af16e48f-746b-4a12-aae1-c14dcee429e0).
> > > >
> > > > If you do this why do not add also a GRUB command to dump all PCRs,
> > > > including DRTM ones.
> > > >
> > > Sure, a new command would be helpful to inspect PCRs with GRUB shell.
> > > I'll add the command in v3.
> > >
> > There is one problem with the command. Since GRUB always measures the
> > commands into PCR 8, so the PCR dump command may also affect PCR 8 and
> > the user may never get a stable PCR 8.
> 
> It is a problem with every GRUB command, even ls. So, I would not care
> much here. Though I think we should add a blurb to the GRUB documentation
> saying about side effect of running commands from the GRUB shell.
> 
> And I would add a GRUB command, including its documentation, in the
> separate patch. So, we will have two patches then... Or three if we
> count a blurb mentioned above as a separate patch.
> 
Okay. I have another patch series to improve the NV index support, and
I'll merge this patch into that patchset with two more patches: one for
the command and the other for the document.

Gary Lin