[PATCH v2] tpm: Lock TPM chip in tpm_pm_suspend() first

[Jarkko Sakkinen]

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: sta...@vger.kernel.org # v6.4+
Fixes: 99d464506255 ("tpm: Prevent hwrng from activating during resume")
Reported-by: Mike Seo <mikeseohyung...@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219383
Signed-off-by: Jarkko Sakkinen <jar...@kernel.org>
---
v2:
- Addressed my own remark:
  https://lore.kernel.org/linux-integrity/d59jai6rr2cd.g5e5t4zcz...@kernel.org/
---
 drivers/char/tpm/tpm-interface.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 8134f002b121..e37fcf9361bc 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -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);
-- 
2.47.0