tpm: End any active auth session before shutdown

From: Jonathan McDowell <[email protected]>

Lazy flushing of TPM auth sessions can interact badly with IMA + kexec, resulting in loaded session handles being leaked across the kexec and not cleaned up. Fix by ensuring any active auth session is ended before the TPM is told about the shutdown, matching what is done when suspending.

Before:

root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~# kexec --load --kexec-file-syscall …
root@debian-qemu-efi:~# systemctl kexec
…
root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
- 0x2000000
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~#
(repeat kexec steps)
root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
- 0x2000000
- 0x2000001
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~#

After:

root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~# kexec --load --kexec-file-syscall …
root@debian-qemu-efi:~# systemctl kexec
…
root@debian-qemu-efi:~# tpm2_getcap handles-loaded-session
root@debian-qemu-efi:~# tpm2_getcap handles-saved-session
root@debian-qemu-efi:~#

Signed-off-by Jonathan McDowell <[email protected]>

---
drivers/char/tpm/tpm-chip.c | 1 +

1 file changed, 1 insertion(+)

drivers/char/tpm/tpm-chip.c +1 -0

index 7df7abaf3e52..87f01269b9b5 100644
@@ -300,6 +300,7 @@ int tpm_class_shutdown(struct device *dev)
 	down_write(&chip->ops_sem);
 	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
 		if (!tpm_chip_start(chip)) {
+			tpm2_end_auth_session(chip);
 			tpm2_shutdown(chip, TPM2_SU_CLEAR);
 			tpm_chip_stop(chip);
 		}

Signature · 1 line

2.48.1

Gentle poke about this patch, which I haven't seen any feedback for. It's causing us a problem in terms of having a string of kexecs result in the kernel no longer being able to talk to the TPM with an HMAC session, and the rng random data fetches from the TPM then failing.