tpm: Prevent hwrng from activating during resume

Set TPM_CHIP_FLAG_SUSPENDED in tpm_pm_suspend() and reset in
tpm_pm_resume(). While the flag is set, tpm_hwrng() gives back zero
bytes. This prevents hwrng from racing during resume.

Cc: stable@vger.kernel.org
Fixes: 6e592a065d51 ("tpm: Move Linux RNG connection to hwrng")
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index c10a4aa..cd48033 100644 (file)
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -571,6 +571,10 @@ 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 4463d00..586ca10 100644 (file)
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -412,6 +412,8 @@ int tpm_pm_suspend(struct device *dev)
        }
 
 suspended:
+       chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
+
        if (rc)
                dev_err(dev, "Ignoring error %d while suspending\n", rc);
        return 0;
@@ -429,6 +431,14 @@ int tpm_pm_resume(struct device *dev)
        if (chip == NULL)
                return -ENODEV;
 
+       chip->flags &= ~TPM_CHIP_FLAG_SUSPENDED;
+
+       /*
+        * Guarantee that SUSPENDED is written last, so that hwrng does not
+        * activate before the chip has been fully resumed.
+        */
+       wmb();
+
        return 0;
 }
 EXPORT_SYMBOL_GPL(tpm_pm_resume);

diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 7769338..6a1e8f1 100644 (file)
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -282,6 +282,7 @@ enum tpm_chip_flags {
        TPM_CHIP_FLAG_ALWAYS_POWERED            = BIT(5),
        TPM_CHIP_FLAG_FIRMWARE_POWER_MANAGED    = BIT(6),
        TPM_CHIP_FLAG_FIRMWARE_UPGRADE          = BIT(7),
+       TPM_CHIP_FLAG_SUSPENDED                 = BIT(8),
 };
 
 #define to_tpm_chip(d) container_of(d, struct tpm_chip, dev)