[tpmdd-devel] [PATCH RESEND 3/3] tpm-chip: Export TPM device to user space even when startup failed

[Michal Suchánek]

On Wed, 30 Aug 2017 13:20:02 +0300
Jarkko Sakkinen <jarkko.sakkinen at linux.intel.com> wrote:

> On Wed, Aug 30, 2017 at 01:15:10PM +0300, Jarkko Sakkinen wrote:
> > On Tue, Aug 29, 2017 at 03:17:39PM +0200, Michal Suchánek wrote:  
> > > Hello,
> > > 
> > > On Tue, 29 Aug 2017 15:55:09 +0300
> > > Jarkko Sakkinen <jarkko.sakkinen at linux.intel.com> wrote:
> > >   
> > > > On Mon, Aug 28, 2017 at 05:15:58PM +0000,
> > > > Alexander.Steffen at infineon.com wrote:  
> > > > > But is that just because nobody bothered to implement the
> > > > > necessary logic or for some other reason?    
> > > > 
> > > > We do not want user space to access broken hardware. It's a
> > > > huge risk for system stability and potentially could be used
> > > > for evil purposes.
> > > > 
> > > > This is not going to mainline as it is not suitable for general
> > > > consumption. You must use a patched kernel if you want this.
> > > > 
> > > > /Jarkko
> > > >   
> > > 
> > > It has been pointed out that userspace applications that use
> > > direct IO access exist for the purpose. So using a kernel driver
> > > is an improvement over that if the interface is otherwise sane.
> > > 
> > > What do you expect is the potential for instability or evil use?  
> > 
> > By definition the use of broken hardware can have unpredictable
> > effects. Use a patched kernel if you want to do it.
> > 
> > /Jarkko  
> 
> I.e. too many unknown unknowns for mainline.
> 
> I could consider a solution for the TPM error case on self-test that
> allows only restricted subset of commands.
> 
> The patch description did not go to *any* detail on how it is used so
> practically it's unreviewable at this point. There's a big burder of
> proof and now there's only hand waving.
> 
Hello,

there was a bug patched recently in which Linux was not sending the
shutdown command on system shutdown. Presumably with this bug some TPMs
consider being under attack and stop performing most functions.
However, you should be able to read the log if this is implemented
sanely. For that the TPM needs to be accessible.

There are probably other cases when the TPM might be useless for system
use but it might be useful to access it. For example, does Linux handle
uninitialized TPMs?

Thanks

Michal
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