TPM+IMA: tpm_add_char_device() is taking too long for IMA to detect TPM
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 42/100
- Issue type
- Bug
- Clarity
- Mostly clear
- Activity status
- Stale
- Tech stack
- c
- Domain
- operating-systems, security
Research direction
Trace the startup ordering between ima_init(), tpm_default_chip(), tpm_add_char_device(), idr_get_next(), and idr_replace(). Reproduce on the Raspberry Pi 4 with the Infineon SLB9670 using the reported 5.15.30 kernel and capture boot logs around the TPM messages. Done means IMA detects the TPM instead of activating TPM-bypass when the TPM becomes available.
Written by the indexing model from the issue text.
Description
Describe the bug
I'm using a Raspberry 4 with kernel linux 5.15.y and i kit my board with a TPM Infineon SLB9670.
I've noticed that in the function ima_init() there is a call to tpm_default_chip() that should return a valid tpm instance, but in my case always fails to "No TPM chip found, activating TPM-bypass!\n". In that function there is a call to idr_get_next() which return NULL, because the idr_replace() function in tpm_add_char_device() is called after the call to ima_init()->tpm_default_chip().
In the picture the idr_replace() is call at second 2 ("tpm: TPM available" print) which is after ima_init calls tpm_default_chip to get the tpm (which it takes only 1.73 seconds).
Steps to reproduce the behaviour
.
Device (s)
Raspberry Pi 4 Mod. B
System
OS: rpi-5.15.30
Kernel: linux-5.15.30
Logs
No response
Additional context
No response
- Dominant language
- C
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