linux-kernel - [PATCH v3] char: tpm: Protect tpm_pm

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Message-Id: <20221128195651.322822-1-Jason@zx2c4.com>
Date:   Mon, 28 Nov 2022 20:56:51 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jan Dąbroś <jsd@...ihalf.com>,
        linux-integrity@...r.kernel.org, peterhuewe@....de, jgg@...pe.ca,
        gregkh@...uxfoundation.org, arnd@...db.de, rrangel@...omium.org,
        timvp@...gle.com, apronin@...gle.com, mw@...ihalf.com,
        upstream@...ihalf.com, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org
Cc:     "Jason A . Donenfeld" <Jason@...c4.com>, stable@...r.kernel.org
Subject: [PATCH v3] char: tpm: Protect tpm_pm_suspend with locks

From: Jan Dabros <jsd@...ihalf.com>

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:

[    3.277834] tpm tpm0: tpm_transmit: tpm_recv: error -52
[    3.278437] tpm tpm0: invalid TPM_STS.x 0xff, dumping stack for forensics
[    3.278445] CPU: 0 PID: 1 Comm: init Not tainted 6.1.0-rc5+ #135
[    3.278450] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-20220807_005459-localhost 04/01/2014
[    3.278453] Call Trace:
[    3.278458]  <TASK>
[    3.278460]  dump_stack_lvl+0x34/0x44
[    3.278471]  tpm_tis_status.cold+0x19/0x20
[    3.278479]  tpm_transmit+0x13b/0x390
[    3.278489]  tpm_transmit_cmd+0x20/0x80
[    3.278496]  tpm1_pm_suspend+0xa6/0x110
[    3.278503]  tpm_pm_suspend+0x53/0x80
[    3.278510]  __pnp_bus_suspend+0x35/0xe0
[    3.278515]  ? pnp_bus_freeze+0x10/0x10
[    3.278519]  __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 <jsd@...ihalf.com>
Reported-by: Vlastimil Babka <vbabka@...e.cz>
Tested-by: Jason A. Donenfeld <Jason@...c4.com>
Tested-by: Vlastimil Babka <vbabka@...e.cz>
Link: https://lore.kernel.org/all/c5ba47ef-393f-1fba-30bd-1230d1b4b592@suse.cz/
Cc: stable@...r.kernel.org
Fixes: e891db1a18bf ("tpm: turn on TPM on suspend for TPM 1.x")
[Jason: reworked commit message, added metadata]
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
 drivers/char/tpm/tpm-interface.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 1621ce818705..d69905233aff 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/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:
-- 
2.38.1