Concurrent accesses to the tpm chip are prevented by allowing only a
single thread at a time to obtain a tpm chip reference through
tpm_try_get_ops(). However, the tpm's suspend function does not use
this mechanism, so when the tpm api is called by a kthread which
does not get frozen on suspend (such as the hw_random kthread)
it's possible that the tpm is used when already in suspend, or
in use while in the process of suspending.
This is seen on certain ChromeOS platforms - low-probability warnings
are generated during suspend. In this case, the tpm attempted to read data
from a tpm chip on an already-suspended bus.
i2c_designware i2c_designware.1: Transfer while suspended
Fix:
1. prevent concurrent execution of tpm accesses and suspend/
resume, by letting suspend/resume grab the tpm_mutex.
2. before commencing a tpm access, check if the tpm chip is already
suspended. Fail with -EAGAIN if so.
Tested by running 6000 suspend/resume cycles back-to-back on a
ChromeOS "brya" device. The intermittent warnings reliably
disappear after applying this patch. No system issues were observed.
Cc: <[email protected]>
Fixes: e891db1a18bf ("tpm: turn on TPM on suspend for TPM 1.x")
Signed-off-by: Sven van Ashbrook <[email protected]>
---
drivers/char/tpm/tpm-interface.c | 16 ++++++++++++++++
include/linux/tpm.h | 2 ++
2 files changed, 18 insertions(+)
diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 1621ce818705..16ca490fd483 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -82,6 +82,11 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
return -E2BIG;
}
+ if (chip->is_suspended) {
+ dev_info(&chip->dev, "blocking transmit while suspended\n");
+ return -EAGAIN;
+ }
+
rc = chip->ops->send(chip, buf, count);
if (rc < 0) {
if (rc != -EPIPE)
@@ -394,6 +399,8 @@ int tpm_pm_suspend(struct device *dev)
if (!chip)
return -ENODEV;
+ mutex_lock(&chip->tpm_mutex);
+
if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
goto suspended;
@@ -411,6 +418,11 @@ int tpm_pm_suspend(struct device *dev)
}
suspended:
+ if (!rc)
+ chip->is_suspended = true;
+
+ mutex_unlock(&chip->tpm_mutex);
+
return rc;
}
EXPORT_SYMBOL_GPL(tpm_pm_suspend);
@@ -426,6 +438,10 @@ int tpm_pm_resume(struct device *dev)
if (chip == NULL)
return -ENODEV;
+ mutex_lock(&chip->tpm_mutex);
+ chip->is_suspended = false;
+ mutex_unlock(&chip->tpm_mutex);
+
return 0;
}
EXPORT_SYMBOL_GPL(tpm_pm_resume);
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index d7c67581929f..0fbc1a43ae80 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -131,6 +131,8 @@ struct tpm_chip {
int dev_num; /* /dev/tpm# */
unsigned long is_open; /* only one allowed */
+ bool is_suspended;
+
char hwrng_name[64];
struct hwrng hwrng;
--
2.37.1.559.g78731f0fdb-goog
On Tue, Aug 09, 2022 at 07:39:18PM +0000, Sven van Ashbrook wrote:
> Concurrent accesses to the tpm chip are prevented by allowing only a
> single thread at a time to obtain a tpm chip reference through
> tpm_try_get_ops(). However, the tpm's suspend function does not use
> this mechanism, so when the tpm api is called by a kthread which
> does not get frozen on suspend (such as the hw_random kthread)
> it's possible that the tpm is used when already in suspend, or
> in use while in the process of suspending.
>
> This is seen on certain ChromeOS platforms - low-probability warnings
> are generated during suspend. In this case, the tpm attempted to read data
> from a tpm chip on an already-suspended bus.
>
> i2c_designware i2c_designware.1: Transfer while suspended
>
> Fix:
> 1. prevent concurrent execution of tpm accesses and suspend/
> resume, by letting suspend/resume grab the tpm_mutex.
> 2. before commencing a tpm access, check if the tpm chip is already
> suspended. Fail with -EAGAIN if so.
>
> Tested by running 6000 suspend/resume cycles back-to-back on a
> ChromeOS "brya" device. The intermittent warnings reliably
> disappear after applying this patch. No system issues were observed.
>
> Cc: <[email protected]>
> Fixes: e891db1a18bf ("tpm: turn on TPM on suspend for TPM 1.x")
> Signed-off-by: Sven van Ashbrook <[email protected]>
> ---
> drivers/char/tpm/tpm-interface.c | 16 ++++++++++++++++
> include/linux/tpm.h | 2 ++
> 2 files changed, 18 insertions(+)
>
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 1621ce818705..16ca490fd483 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -82,6 +82,11 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip, void *buf, size_t bufsiz)
> return -E2BIG;
> }
>
> + if (chip->is_suspended) {
> + dev_info(&chip->dev, "blocking transmit while suspended\n");
> + return -EAGAIN;
> + }
> +
> rc = chip->ops->send(chip, buf, count);
> if (rc < 0) {
> if (rc != -EPIPE)
> @@ -394,6 +399,8 @@ int tpm_pm_suspend(struct device *dev)
> if (!chip)
> return -ENODEV;
>
> + mutex_lock(&chip->tpm_mutex);
> +
> if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
> goto suspended;
>
> @@ -411,6 +418,11 @@ int tpm_pm_suspend(struct device *dev)
> }
>
> suspended:
> + if (!rc)
> + chip->is_suspended = true;
> +
> + mutex_unlock(&chip->tpm_mutex);
> +
> return rc;
> }
> EXPORT_SYMBOL_GPL(tpm_pm_suspend);
> @@ -426,6 +438,10 @@ int tpm_pm_resume(struct device *dev)
> if (chip == NULL)
> return -ENODEV;
>
> + mutex_lock(&chip->tpm_mutex);
> + chip->is_suspended = false;
> + mutex_unlock(&chip->tpm_mutex);
> +
> return 0;
> }
> EXPORT_SYMBOL_GPL(tpm_pm_resume);
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index d7c67581929f..0fbc1a43ae80 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -131,6 +131,8 @@ struct tpm_chip {
> int dev_num; /* /dev/tpm# */
> unsigned long is_open; /* only one allowed */
>
> + bool is_suspended;
> +
> char hwrng_name[64];
> struct hwrng hwrng;
>
> --
> 2.37.1.559.g78731f0fdb-goog
>
What about adding TPM_CHIP_FLAG_SUSPENDED instead?
BR, Jarkko
On Thu, Aug 11, 2022 at 1:02 AM Jarkko Sakkinen <[email protected]> wrote:
>
> What about adding TPM_CHIP_FLAG_SUSPENDED instead?
Thank you for the feedback, Jarkko. After thinking this over, I
believe this patch only moves kernel warnings around. Will re-post
soon with a fresh approach, intended to fix the underlying issue
rather than the symptom.
So please disregard this patch.
On Thu, Aug 11, 2022 at 09:09:38AM -0400, Sven van Ashbrook wrote:
> On Thu, Aug 11, 2022 at 1:02 AM Jarkko Sakkinen <[email protected]> wrote:
> >
> > What about adding TPM_CHIP_FLAG_SUSPENDED instead?
>
> Thank you for the feedback, Jarkko. After thinking this over, I
> believe this patch only moves kernel warnings around. Will re-post
> soon with a fresh approach, intended to fix the underlying issue
> rather than the symptom.
>
> So please disregard this patch.
np
BR, Jarkko