tpm: Lock TPM chip in tpm_pm_suspend() first

PATCH Superseded Jarkko Sakkinen 1 participant 1 message Oct 31, 2024

Subsystems (3)

Stable branch Keys-trusted TPM device driver

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Jarkko Sakkinen

author maintainer

2024-10-31 00:45 UTC #0 lore raw

PATCH v2 1/1 tpm: Lock TPM chip in tpm_pm_suspend() first

Setting TPM_CHIP_FLAG_SUSPENDED in the end of tpm_pm_suspend() can be racy according to the bug report, as this leaves window for tpm_hwrng_read() to be called while the operation is in progress.

To address this, lock the TPM chip before checking any possible flags. This will guarantee that tpm_hwrng_read() and tpm_pm_suspend() won't conflict with each other.

Cc [email protected] # v6.4+

Fixes 99d464506255 ("tpm: Prevent hwrng from activating during resume")

Reported-by Mike Seo <[email protected]>

Closes https://bugzilla.kernel.org/show_bug.cgi?id=219383

Signed-off-by Jarkko Sakkinen <[email protected]>

---
v2:
- Addressed my own remark:
https://lore.kernel.org/linux-integrity/[email protected]/

---
 drivers/char/tpm/tpm-interface.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

drivers/char/tpm/tpm-interface.c +16 ~~-10~~

index 8134f002b121..e37fcf9361bc 100644
@@ -370,6 +370,13 @@ int tpm_pm_suspend(struct device *dev)
 	if (!chip)
 		return -ENODEV;
 
+	rc = tpm_try_get_ops(chip);
+	if (rc) {
+		/* Can be safely set out of locks, as no action cannot race: */
+		chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
+		goto out;
+	}
+
 	if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
 		goto suspended;

@@ -377,23 +384,22 @@ int tpm_pm_suspend(struct device *dev)
 	    !pm_suspend_via_firmware())
 		goto suspended;
 
-	rc = tpm_try_get_ops(chip);
-	if (!rc) {
-		if (chip->flags & TPM_CHIP_FLAG_TPM2) {
-			tpm2_end_auth_session(chip);
-			tpm2_shutdown(chip, TPM2_SU_STATE);
-		} else {
-			rc = tpm1_pm_suspend(chip, tpm_suspend_pcr);
-		}
-
-		tpm_put_ops(chip);
+	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+		tpm2_end_auth_session(chip);
+		tpm2_shutdown(chip, TPM2_SU_STATE);
+		goto suspended;
 	}
 
+	rc = tpm1_pm_suspend(chip, tpm_suspend_pcr);
+
 suspended:
 	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
+	tpm_put_ops(chip);
 
+out:
 	if (rc)
 		dev_err(dev, "Ignoring error %d while suspending\n", rc);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(tpm_pm_suspend);

Signature · 1 line

2.47.0