[SeaBIOS] [PATCH 00/10] Some TPM simplifications
Kevin O'Connor
kevin at koconnor.net
Tue Jan 5 21:35:35 CET 2016
On Tue, Jan 05, 2016 at 02:05:55PM -0500, Stefan Berger wrote:
> "Kevin O'Connor" <kevin at koconnor.net> wrote on 01/05/2016 12:16:18 PM:
> > On Tue, Dec 29, 2015 at 07:17:40PM -0500, Kevin O'Connor wrote:
> > > The following series involves some code reorganization in the TPM code
> > > that I found useful in understanding the code.
> >
> > FYI, I committed patches 1-9 (after some bug fixes).
>
> The result of the 2nd patch set also looks good.
Thanks - I pushed most of that series as well.
I've been looking further at error recovery in the TPM code. I'm not
sure I fully understand what needs to be done on an error.
If I understand it correctly, the SeaBIOS TPM code has three major
requirements:
- Pass through commands from the 16bit bios interface to the TPM.
This is useful for bootloaders/oproms that don't have a TPM driver.
- I think the only requirement for error recovery here is that we
return an appropriate error code to the caller of the 16bit BIOS
interface.
- Take "measurements" during the boot process so that later on users
can verify if some low-level code has changed (and thus attempt to
identify if malicious code may have been inserted into the
firmware).
- The major requirement here seems to be that if we can't take a
measurement that we either "cap" measurements or shutdown the TPM.
If we don't do this, it opens the possibility of a malicious
program forging measurements.
- It's also useful to skip taking measurements if the TPM device is
not present so that we don't waste CPU time taking measurements
that will never be used.
- Implement physical presence capability so that critical settings in
the TPM can only be changed by someone that can prove they are
physically present at the hardware (and thus attempt to prevent
malicious code that temporarily obtains escalated privileges from
altering these important settings).
- The major requirement here seems to be that the "physical
presence" lock always be set prior to starting the boot loader.
And, of course, we need to implement the ability to change the
critical settings (via the tpm menu).
Does the above seem correct?
-Kevin
More information about the SeaBIOS
mailing list