Messages in this thread | | | Subject | Re: [PATCH v2 1/4] tpm: Implement tpm_chip_find() and tpm_chip_put() for other subsystems | From | Stefan Berger <> | Date | Thu, 21 Jun 2018 14:19:44 -0400 |
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On 06/21/2018 01:56 PM, Jason Gunthorpe wrote: > On Thu, Jun 21, 2018 at 01:45:03PM -0400, Stefan Berger wrote: >> On 06/21/2018 01:15 PM, Jarkko Sakkinen wrote: >>> On Wed, Jun 20, 2018 at 04:42:33PM -0400, Stefan Berger wrote: >>>> Implement tpm_chip_find() for other subsystems to find a TPM chip and >>>> get a reference to that chip. Once done with using the chip, the reference >>>> is released using tpm_chip_put(). >>>> >>>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com> >>> You should sort this out in a way that we don't end up with duplicate >>> functions. >> Do you want me to create a function *like* tpm_chip_find_get() that takes an >> additional parameter whether to get the ops semaphore and have that function >> called by the existing tpm_chip_find_get() and the new tpm_chip_find(). The >> latter would then not get the ops semphore. I didn't want to do this since >> one time the function returns with a lock held and the other time not. > Another option, and I haven't looked, is to revise the callers of > tpm_chip_find_get to not require it to hold the ops semaphore for > them.
We have tpm_chip_unregister calling tpm_del_char_device to set the ops to NULL once a chip is unregistered. All existing callers, if they pass in a tpm_chip != NULL, currently fail if the ops are NULL. (If they pass in tpm_chip = NULL, they shouldn't find a chip once ops are null and it has been removed from the IDR). I wouldn't change that since IMA will call in with a tpm_chip != NULL and we want to protect the ops. All existing code within the tpm subsystem does seem to call tpm_chip_find_get() with a NULL pointer, though. Also trusted keys seems to pass in a NULL pointer every time.
> > Either by giving them an API to do it, or revising the TPM entry > points to do it. > > I didn't look, but how did the ops semaphore get grabbed in your > revised patches? They do grab it, right?
The revised patches do not touch the existing code much but will call tpm_chip_find_get() and get that semaphore every time before the ops are used. IMA is the only caller of tpm_chip_find() that now gets an additional reference to the tpm_chip and these APIs get called like this from IMA:
ima init: chip = tpm_chip_find()
ima::tpm: tpm_chip_find_get(chip) ... tpm_put_ops(chip)
ima::tpm: tpm_chip_find_get(chip) ... tpm_put_ops(chip)
[repeat]
ima shutdown: tpm_chip_put(chip)
Stefan
> > Jason >
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