On Fri, May 04, 2018 at 02:56:25PM -0500, David R. Bild wrote: > On Fri, May 4, 2018 at 2:06 PM, Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > > > On Fri, May 04, 2018 at 08:00:22AM -0500, David R. Bild wrote: > > > Normally the system platform (i.e., BIOS/UEFI for x86) is responsible > > > for performing initialization of the TPM. For these modules, the host > > > kernel is the platform, so we perform the initialization in the driver > > > before registering the TPM with the kernel TPM subsystem. > > > > The tpm driver already does most of this stuff automatically, why > > duplicate it there and why is it coded in a way that doesn't use the > > existing TPM services to do it? > > I didn't want to have to duplicate all that functionality and was > disappointed when that became the only option (due to the two reasons > outlined below) for supporting existing kernels with an out-of-tree > module. > > Bringing the module in-tree opens the option of reworking some of the > TPM subsystem to support this use case. I'm open to concrete > suggestions on how to do so. > > 1) The first reason is that I don't think the necessary pieces are > currently made available for reuse. I'd love to not repeat that code, > but > > - some required structs and functions are declared in private headers > (drivers/char/tpm/*.h instead of include/linux/tpm.h). > - many of the required functions are not exported. > > If the TPM maintainers are open to more of the API being "public", I > can look into preparing patches that export the necessary operations. > > 2) The second reason is that the initialization done by the driver is > work that should be done by platform, before the kernel ever sees the > TPM. This is too speculative to give any confirmitive promises. Do not fully understand the reasoning. For example: why should I care about out-of-tree modules? I can look code changes but the text above contains too many words to nail anything down. I'm confused. > In particular, it sets the credentials for the platform hierarchy. > The platform hierarchy is essentially the "root" account of the TPM, > so it's critical that those credentials be set before the TPM is > exposed to user-space. (The platform credentials aren't persisted in > the TPM and must be set by the platform on every boot.) If the driver > registers the TPM before doing initialization, there's a chance that > something else could access the TPM before the platform credentials > get set. Maybe. Not sure yet where to draw the line eg should TSS2 daemon to do it for example. James? Philip? /Jarkko
