Re: [PATCH v3] tpm: Lock TPM chip in tpm_pm_suspend() first

On Fri, Nov 01, 2024 at 02:21:56AM +0200, Jarkko Sakkinen wrote:

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

Aadress this by locking the TPM chip before checking any chip->flags both in tpm_pm_suspend() and tpm_hwrng_read(). Move TPM_CHIP_FLAG_SUSPENDED check inside tpm_get_random() so that it will be always checked only when the lock is reserved.

Cc: stable@vger.kernel.org # v6.4+ Fixes: 99d464506255 ("tpm: Prevent hwrng from activating during resume") Reported-by: Mike Seo mikeseohyungjin@gmail.com Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219383 Signed-off-by: Jarkko Sakkinen jarkko@kernel.org

---

v3:

• Check TPM_CHIP_FLAG_SUSPENDED inside tpm_get_random() so that it is also done under the lock (suggested by Jerry Snitselaar).

v2:

• Addressed my own remark: https://lore.kernel.org/linux-integrity/D59JAI6RR2CD.G5E5T4ZCZ49W@kernel.org...

---

drivers/char/tpm/tpm-chip.c | 4 ---- drivers/char/tpm/tpm-interface.c | 32 ++++++++++++++++++++++---------- 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c index 1ff99a7091bb..7df7abaf3e52 100644 --- a/drivers/char/tpm/tpm-chip.c +++ b/drivers/char/tpm/tpm-chip.c @@ -525,10 +525,6 @@ static int tpm_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait) { struct tpm_chip *chip = container_of(rng, struct tpm_chip, hwrng);

• /* Give back zero bytes, as TPM chip has not yet fully resumed: */
• if (chip->flags & TPM_CHIP_FLAG_SUSPENDED)

• return 0;
  

• return tpm_get_random(chip, data, max);

} diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c index 8134f002b121..b1daa0d7b341 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;

@@ -377,21 +384,19 @@ 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);

I imagine the above still be wrapped in an else with the if (chip->flags & TPM_CHIP_FLAG_TPM2) otherwise it will call tpm1_pm_suspend for both tpm1 and tpm2 devices, yes?

So:

if (chip->flags & TPM_CHIP_FLAG_TPM2) { tpm2_end_auth_session(chip); tpm2_shutdown(chip, TPM2_SU_STATE); goto suspended; } else { rc = tpm1_pm_suspend(chip, tpm_suspend_pcr); }

Other than that I think it looks good.

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; @@ -440,11 +445,18 @@ int tpm_get_random(struct tpm_chip *chip, u8 *out, size_t max) if (!chip) return -ENODEV;

• /* Give back zero bytes, as TPM chip has not yet fully resumed: */
• if (chip->flags & TPM_CHIP_FLAG_SUSPENDED) {

• rc = 0;
  

• goto out;
  

• }
• if (chip->flags & TPM_CHIP_FLAG_TPM2) rc = tpm2_get_random(chip, out, max); else rc = tpm1_get_random(chip, out, max);

+out: tpm_put_ops(chip); return rc; } -- 2.47.0