From: Daniel Kiper <daniel.kiper@oracle.com>
To: Brendan Trotter <btrotter@gmail.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>,
The development of GNU GRUB <grub-devel@gnu.org>,
Ard Biesheuvel <ardb@kernel.org>,
Alec Brown <alec.r.brown@oracle.com>,
Kanth Ghatraju <kanth.ghatraju@oracle.com>,
Ross Philipson <ross.philipson@oracle.com>,
"piotr.krol@3mdeb.com" <piotr.krol@3mdeb.com>,
"krystian.hebel@3mdeb.com" <krystian.hebel@3mdeb.com>,
"persaur@gmail.com" <persaur@gmail.com>,
"Yoder, Stuart" <stuart.yoder@arm.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
"michal.zygowski@3mdeb.com" <michal.zygowski@3mdeb.com>,
James Bottomley <James.Bottomley@hansenpartnership.com>,
"lukasz@hawrylko.pl" <lukasz@hawrylko.pl>,
linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
James Morris <jmorris@namei.org>,
dpsmith@apertussolutions.com
Subject: Re: Linux DRTM on UEFI platforms
Date: Thu, 11 Aug 2022 13:34:56 +0200 [thread overview]
Message-ID: <20220811113456.dweldtx6gespvrwn@tomti.i.net-space.pl> (raw)
In-Reply-To: <CAELHeEdNgYCh_kQwWpEc4aXw-YL-KGrAeDCL-VaG3ChFs6LNVw@mail.gmail.com>
On Thu, Aug 11, 2022 at 07:25:58PM +0930, Brendan Trotter wrote:
> Hi,
>
> On Thu, Aug 11, 2022 at 3:16 AM Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> > On Wed, Aug 10, 2022 at 06:37:18PM +0930, Brendan Trotter wrote:
> >
> > > [1] doesn't provide any useful information. How does a kernel know
> > > that the callback provided by boot loader actually measures what it's
> > > supposed to measure, or even does anything at all?
> >
> > The kernel has no way to know this - *any* code you've run before
> > performing a measurement could tamper with the kernel such that it
> > believes it's fine. This is just as true in DRTM as it is in SRTM. But
> > you know what the expected measurements should be, so you're able to
> > either seal secrets to those PCR values or rely on remote attestation.
>
> In this scenario the kernel has no idea what the measurement should
> be, it only knows the measurement that a potentially malicious boot
> loader felt like giving the kernel previously (e.g. when the kernel
> was installed).
>
> > > [1] doesn't provide any useful information. Senter and skinit don't
> > > provide a method for kernel to detect that (e.g.) a MiTM boot loader
> > > has always measured a forgery and has changed unmeasured code in a
> > > different way every time you boot.
> >
> > Measurements are not opaque objects. If you're not able to reconstruct
> > the expected measurement then you're doing it wrong.
>
> OK; so to detect if boot loader has always given kernel a bad/forged
> measurement; the kernel repeats all of the steps involved in creating
> the measurement itself exactly the same as the boot loader should have
> (but might not have) so that kernel can compare a "known
> good/trustworthy" measurement with the useless measurement that the
> boot loader created for no sane reason whatsoever?
Could you tell us where exactly boot loader creates measurements for the DRTM?
Daniel
next prev parent reply other threads:[~2022-08-11 11:35 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-29 17:40 Linux DRTM on UEFI platforms Matthew Garrett
2022-03-30 7:02 ` Ard Biesheuvel
2022-03-30 7:11 ` Matthew Garrett
2022-03-30 7:12 ` Ard Biesheuvel
2022-03-30 7:18 ` Matthew Garrett
2022-03-30 7:23 ` Ard Biesheuvel
2022-03-30 7:27 ` Matthew Garrett
2022-03-30 7:39 ` Ard Biesheuvel
2022-03-30 12:46 ` James Bottomley
2022-03-31 0:35 ` Daniel P. Smith
2022-03-31 7:13 ` Ard Biesheuvel
2022-03-31 10:59 ` Heinrich Schuchardt
2022-05-19 20:57 ` Daniel P. Smith
2022-05-19 20:57 ` Daniel P. Smith
2022-06-10 16:40 ` Ard Biesheuvel
2022-07-05 18:35 ` Daniel P. Smith
2022-07-06 0:03 ` Brendan Trotter
2022-07-06 0:12 ` Matthew Garrett
2022-07-07 9:46 ` Daniel P. Smith
2022-07-08 3:36 ` Brendan Trotter
2022-07-08 4:56 ` Matthew Garrett
2022-07-22 17:23 ` Daniel P. Smith
2022-07-23 5:15 ` Brendan Trotter
2022-08-09 10:53 ` Daniel P. Smith
2022-08-10 9:07 ` Brendan Trotter
2022-08-10 17:46 ` Matthew Garrett
2022-08-11 9:55 ` Brendan Trotter
2022-08-11 11:34 ` Daniel Kiper [this message]
2022-08-11 18:25 ` Matthew Garrett
2022-08-12 3:22 ` Brendan Trotter
2022-08-12 5:54 ` Matthew Garrett
2022-08-05 12:53 ` Ard Biesheuvel
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