char: tpm: Protect tpm_pm_suspend with locks

Currently tpm transactions are executed unconditionally in
tpm_pm_suspend() function, which may lead to races with other tpm
accessors in the system.

Specifically, the hw_random tpm driver makes use of tpm_get_random(),
and this function is called in a loop from a kthread, which means it's
not frozen alongside userspace, and so can race with the work done
during system suspend:

  tpm tpm0: tpm_transmit: tpm_recv: error -52
  tpm tpm0: invalid TPM_STS.x 0xff, dumping stack for forensics
  CPU: 0 PID: 1 Comm: init Not tainted 6.1.0-rc5+ #135
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-20220807_005459-localhost 04/01/2014
  Call Trace:
   tpm_tis_status.cold+0x19/0x20
   tpm_transmit+0x13b/0x390
   tpm_transmit_cmd+0x20/0x80
   tpm1_pm_suspend+0xa6/0x110
   tpm_pm_suspend+0x53/0x80
   __pnp_bus_suspend+0x35/0xe0
   __device_suspend+0x10f/0x350

Fix this by calling tpm_try_get_ops(), which itself is a wrapper around
tpm_chip_start(), but takes the appropriate mutex.

Signed-off-by: Jan Dabros <[email protected]>
Reported-by: Vlastimil Babka <[email protected]>
Tested-by: Jason A. Donenfeld <[email protected]>
Tested-by: Vlastimil Babka <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Cc: [email protected]
Fixes: e891db1 ("tpm: turn on TPM on suspend for TPM 1.x")
[Jason: reworked commit message, added metadata]
Signed-off-by: Jason A. Donenfeld <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

drivers/char/tpm/tpm-interface.c

@@ -401,13 +401,14 @@ int tpm_pm_suspend(struct device *dev)
 	    !pm_suspend_via_firmware())
 		goto suspended;
 
-	if (!tpm_chip_start(chip)) {
+	rc = tpm_try_get_ops(chip);
+	if (!rc) {
 		if (chip->flags & TPM_CHIP_FLAG_TPM2)
 			tpm2_shutdown(chip, TPM2_SU_STATE);
 		else
 			rc = tpm1_pm_suspend(chip, tpm_suspend_pcr);
 
-		tpm_chip_stop(chip);
+		tpm_put_ops(chip);
 	}
 
 suspended: