tpm: set TPM_CHIP_FLAG_SUSPENDED early

[PATCH] tpm: set TPM_CHIP_FLAG_SUSPENDED early

Posted by Jarkko Sakkinen 3 weeks, 5 days ago

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. Move setting of the flag
into the beginning.

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>
---
 drivers/char/tpm/tpm-interface.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 8134f002b121..3f96bc8b95df 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -370,6 +370,8 @@ int tpm_pm_suspend(struct device *dev)
 	if (!chip)
 		return -ENODEV;
 
+	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
+
 	if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
 		goto suspended;
 
@@ -390,8 +392,6 @@ 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;
-- 
2.47.0

Re: [PATCH] tpm: set TPM_CHIP_FLAG_SUSPENDED early

Posted by Jerry Snitselaar 3 weeks, 4 days ago

On Wed, Oct 30, 2024 at 12:36:47AM +0200, Jarkko Sakkinen wrote:
> 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. Move setting of the flag
> into the beginning.
> 
> 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>
> ---
>  drivers/char/tpm/tpm-interface.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> index 8134f002b121..3f96bc8b95df 100644
> --- a/drivers/char/tpm/tpm-interface.c
> +++ b/drivers/char/tpm/tpm-interface.c
> @@ -370,6 +370,8 @@ int tpm_pm_suspend(struct device *dev)
>  	if (!chip)
>  		return -ENODEV;
>  
> +	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> +
>  	if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
>  		goto suspended;
>  
> @@ -390,8 +392,6 @@ 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;
> -- 
> 2.47.0
> 

Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>

Re: [PATCH] tpm: set TPM_CHIP_FLAG_SUSPENDED early

Posted by Jarkko Sakkinen 3 weeks, 4 days ago

On Wed Oct 30, 2024 at 10:09 PM EET, Jerry Snitselaar wrote:
> On Wed, Oct 30, 2024 at 12:36:47AM +0200, Jarkko Sakkinen wrote:
> > 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. Move setting of the flag
> > into the beginning.
> > 
> > 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>
> > ---
> >  drivers/char/tpm/tpm-interface.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> > index 8134f002b121..3f96bc8b95df 100644
> > --- a/drivers/char/tpm/tpm-interface.c
> > +++ b/drivers/char/tpm/tpm-interface.c
> > @@ -370,6 +370,8 @@ int tpm_pm_suspend(struct device *dev)
> >  	if (!chip)
> >  		return -ENODEV;
> >  
> > +	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> > +
> >  	if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
> >  		goto suspended;
> >  
> > @@ -390,8 +392,6 @@ 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;
> > -- 
> > 2.47.0
> > 
>
> Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>

Thanks but I actually started to look at the function:

https://elixir.bootlin.com/linux/v6.11.5/source/drivers/char/tpm/tpm-interface.c#L365

The absolutely safe-play way considering concurrency would be
to do tpm_try_get_ops() before checking any flags. That way
tpm_hwrng_read() is guaranteed not conflict.

So the way I would fix this instead would be to (untested
wrote inline here):

int tpm_pm_suspend(struct device *dev)
{
	struct tpm_chip *chip = dev_get_drvdata(dev);
	int rc = 0;

	if (!chip)
		return -ENODEV;

	rc = tpm_try_get_ops(chip);
	if (rc) {
		chip->flags = |= TPM_CHIP_FLAG_SUSPENDED;
		return rc;
	}

	/* ... */

suspended:
	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
	tpm_put_ops(chip);

It does not really affect performance but guarantees that
tpm_hwrng_read() is guaranteed either fully finish or
never happens given that both sides take chip->lock.

So I'll put one more round of this and then this should be
stable and fully fixed.

BR, Jarkko

Re: [PATCH] tpm: set TPM_CHIP_FLAG_SUSPENDED early

Posted by Jerry Snitselaar 3 weeks, 3 days ago

On Thu, Oct 31, 2024 at 01:36:46AM +0200, Jarkko Sakkinen wrote:
> On Wed Oct 30, 2024 at 10:09 PM EET, Jerry Snitselaar wrote:
> > On Wed, Oct 30, 2024 at 12:36:47AM +0200, Jarkko Sakkinen wrote:
> > > 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. Move setting of the flag
> > > into the beginning.
> > > 
> > > 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>
> > > ---
> > >  drivers/char/tpm/tpm-interface.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> > > index 8134f002b121..3f96bc8b95df 100644
> > > --- a/drivers/char/tpm/tpm-interface.c
> > > +++ b/drivers/char/tpm/tpm-interface.c
> > > @@ -370,6 +370,8 @@ int tpm_pm_suspend(struct device *dev)
> > >  	if (!chip)
> > >  		return -ENODEV;
> > >  
> > > +	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> > > +
> > >  	if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
> > >  		goto suspended;
> > >  
> > > @@ -390,8 +392,6 @@ 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;
> > > -- 
> > > 2.47.0
> > > 
> >
> > Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> 
> Thanks but I actually started to look at the function:
> 
> https://elixir.bootlin.com/linux/v6.11.5/source/drivers/char/tpm/tpm-interface.c#L365
> 
> The absolutely safe-play way considering concurrency would be
> to do tpm_try_get_ops() before checking any flags. That way
> tpm_hwrng_read() is guaranteed not conflict.
> 
> So the way I would fix this instead would be to (untested
> wrote inline here):
> 
> int tpm_pm_suspend(struct device *dev)
> {
> 	struct tpm_chip *chip = dev_get_drvdata(dev);
> 	int rc = 0;
> 
> 	if (!chip)
> 		return -ENODEV;
> 
> 	rc = tpm_try_get_ops(chip);
> 	if (rc) {
> 		chip->flags = |= TPM_CHIP_FLAG_SUSPENDED;
> 		return rc;
> 	}
> 
> 	/* ... */
> 
> suspended:
> 	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> 	tpm_put_ops(chip);
> 
> It does not really affect performance but guarantees that
> tpm_hwrng_read() is guaranteed either fully finish or
> never happens given that both sides take chip->lock.
> 
> So I'll put one more round of this and then this should be
> stable and fully fixed.
> 
> BR, Jarkko

Ah, yeah better to set it while it has the mutex. That should still be
'if (!rc)' after the tpm_try_get_ops() right? (I'm assuming that is just
a transcription error).

Regards,
Jerry

Re: [PATCH] tpm: set TPM_CHIP_FLAG_SUSPENDED early

Posted by Jerry Snitselaar 3 weeks, 3 days ago

On Thu, Oct 31, 2024 at 08:02:37AM -0700, Jerry Snitselaar wrote:
> On Thu, Oct 31, 2024 at 01:36:46AM +0200, Jarkko Sakkinen wrote:
> > On Wed Oct 30, 2024 at 10:09 PM EET, Jerry Snitselaar wrote:
> > > On Wed, Oct 30, 2024 at 12:36:47AM +0200, Jarkko Sakkinen wrote:
> > > > 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. Move setting of the flag
> > > > into the beginning.
> > > > 
> > > > 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>
> > > > ---
> > > >  drivers/char/tpm/tpm-interface.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> > > > index 8134f002b121..3f96bc8b95df 100644
> > > > --- a/drivers/char/tpm/tpm-interface.c
> > > > +++ b/drivers/char/tpm/tpm-interface.c
> > > > @@ -370,6 +370,8 @@ int tpm_pm_suspend(struct device *dev)
> > > >  	if (!chip)
> > > >  		return -ENODEV;
> > > >  
> > > > +	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> > > > +
> > > >  	if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
> > > >  		goto suspended;
> > > >  
> > > > @@ -390,8 +392,6 @@ 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;
> > > > -- 
> > > > 2.47.0
> > > > 
> > >
> > > Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> > 
> > Thanks but I actually started to look at the function:
> > 
> > https://elixir.bootlin.com/linux/v6.11.5/source/drivers/char/tpm/tpm-interface.c#L365
> > 
> > The absolutely safe-play way considering concurrency would be
> > to do tpm_try_get_ops() before checking any flags. That way
> > tpm_hwrng_read() is guaranteed not conflict.
> > 
> > So the way I would fix this instead would be to (untested
> > wrote inline here):
> > 
> > int tpm_pm_suspend(struct device *dev)
> > {
> > 	struct tpm_chip *chip = dev_get_drvdata(dev);
> > 	int rc = 0;
> > 
> > 	if (!chip)
> > 		return -ENODEV;
> > 
> > 	rc = tpm_try_get_ops(chip);
> > 	if (rc) {
> > 		chip->flags = |= TPM_CHIP_FLAG_SUSPENDED;
> > 		return rc;
> > 	}
> > 
> > 	/* ... */
> > 
> > suspended:
> > 	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> > 	tpm_put_ops(chip);
> > 
> > It does not really affect performance but guarantees that
> > tpm_hwrng_read() is guaranteed either fully finish or
> > never happens given that both sides take chip->lock.
> > 
> > So I'll put one more round of this and then this should be
> > stable and fully fixed.
> > 
> > BR, Jarkko
> 
> Ah, yeah better to set it while it has the mutex. That should still be
> 'if (!rc)' after the tpm_try_get_ops() right? (I'm assuming that is just
> a transcription error).
> 
> Regards,
> Jerry
> 

It has been a while since I've looked at TPM code. Since
tpm_hwrng_read doesn't check the flag with the mutex held is there a
point later where it will bail out if the suspend has occurred? I'm
wondering if the check for the suspend flag in tpm_hwrng_read should
be after the tpm_find_get_ops in tpm_get_random.

Regards,
Jerry

Re: [PATCH] tpm: set TPM_CHIP_FLAG_SUSPENDED early

Posted by Jarkko Sakkinen 3 weeks, 3 days ago

On Thu Oct 31, 2024 at 5:28 PM EET, Jerry Snitselaar wrote:
> On Thu, Oct 31, 2024 at 08:02:37AM -0700, Jerry Snitselaar wrote:
> > On Thu, Oct 31, 2024 at 01:36:46AM +0200, Jarkko Sakkinen wrote:
> > > On Wed Oct 30, 2024 at 10:09 PM EET, Jerry Snitselaar wrote:
> > > > On Wed, Oct 30, 2024 at 12:36:47AM +0200, Jarkko Sakkinen wrote:
> > > > > 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. Move setting of the flag
> > > > > into the beginning.
> > > > > 
> > > > > 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>
> > > > > ---
> > > > >  drivers/char/tpm/tpm-interface.c | 4 ++--
> > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> > > > > index 8134f002b121..3f96bc8b95df 100644
> > > > > --- a/drivers/char/tpm/tpm-interface.c
> > > > > +++ b/drivers/char/tpm/tpm-interface.c
> > > > > @@ -370,6 +370,8 @@ int tpm_pm_suspend(struct device *dev)
> > > > >  	if (!chip)
> > > > >  		return -ENODEV;
> > > > >  
> > > > > +	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> > > > > +
> > > > >  	if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
> > > > >  		goto suspended;
> > > > >  
> > > > > @@ -390,8 +392,6 @@ 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;
> > > > > -- 
> > > > > 2.47.0
> > > > > 
> > > >
> > > > Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> > > 
> > > Thanks but I actually started to look at the function:
> > > 
> > > https://elixir.bootlin.com/linux/v6.11.5/source/drivers/char/tpm/tpm-interface.c#L365
> > > 
> > > The absolutely safe-play way considering concurrency would be
> > > to do tpm_try_get_ops() before checking any flags. That way
> > > tpm_hwrng_read() is guaranteed not conflict.
> > > 
> > > So the way I would fix this instead would be to (untested
> > > wrote inline here):
> > > 
> > > int tpm_pm_suspend(struct device *dev)
> > > {
> > > 	struct tpm_chip *chip = dev_get_drvdata(dev);
> > > 	int rc = 0;
> > > 
> > > 	if (!chip)
> > > 		return -ENODEV;
> > > 
> > > 	rc = tpm_try_get_ops(chip);
> > > 	if (rc) {
> > > 		chip->flags = |= TPM_CHIP_FLAG_SUSPENDED;
> > > 		return rc;
> > > 	}
> > > 
> > > 	/* ... */
> > > 
> > > suspended:
> > > 	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> > > 	tpm_put_ops(chip);
> > > 
> > > It does not really affect performance but guarantees that
> > > tpm_hwrng_read() is guaranteed either fully finish or
> > > never happens given that both sides take chip->lock.
> > > 
> > > So I'll put one more round of this and then this should be
> > > stable and fully fixed.
> > > 
> > > BR, Jarkko
> > 
> > Ah, yeah better to set it while it has the mutex. That should still be
> > 'if (!rc)' after the tpm_try_get_ops() right? (I'm assuming that is just
> > a transcription error).
> > 
> > Regards,
> > Jerry
> > 
>
> It has been a while since I've looked at TPM code. Since
> tpm_hwrng_read doesn't check the flag with the mutex held is there a
> point later where it will bail out if the suspend has occurred? I'm
> wondering if the check for the suspend flag in tpm_hwrng_read should
> be after the tpm_find_get_ops in tpm_get_random.

Right, I ignored that side in v2. Yeah, I agree that in both cases
it would be best that all checks are done when the lock is taken.

It means open-coding tpm2_get_random() but I think it is anyway
good idea (as tpm_get_random() is meant for outside callers).

> Regards,
> Jerry

BR, Jarkko

Re: [PATCH] tpm: set TPM_CHIP_FLAG_SUSPENDED early

Posted by Jarkko Sakkinen 3 weeks, 3 days ago

On Thu Oct 31, 2024 at 5:02 PM EET, Jerry Snitselaar wrote:
> On Thu, Oct 31, 2024 at 01:36:46AM +0200, Jarkko Sakkinen wrote:
> > On Wed Oct 30, 2024 at 10:09 PM EET, Jerry Snitselaar wrote:
> > > On Wed, Oct 30, 2024 at 12:36:47AM +0200, Jarkko Sakkinen wrote:
> > > > 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. Move setting of the flag
> > > > into the beginning.
> > > > 
> > > > 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>
> > > > ---
> > > >  drivers/char/tpm/tpm-interface.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
> > > > index 8134f002b121..3f96bc8b95df 100644
> > > > --- a/drivers/char/tpm/tpm-interface.c
> > > > +++ b/drivers/char/tpm/tpm-interface.c
> > > > @@ -370,6 +370,8 @@ int tpm_pm_suspend(struct device *dev)
> > > >  	if (!chip)
> > > >  		return -ENODEV;
> > > >  
> > > > +	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> > > > +
> > > >  	if (chip->flags & TPM_CHIP_FLAG_ALWAYS_POWERED)
> > > >  		goto suspended;
> > > >  
> > > > @@ -390,8 +392,6 @@ 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;
> > > > -- 
> > > > 2.47.0
> > > > 
> > >
> > > Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
> > 
> > Thanks but I actually started to look at the function:
> > 
> > https://elixir.bootlin.com/linux/v6.11.5/source/drivers/char/tpm/tpm-interface.c#L365
> > 
> > The absolutely safe-play way considering concurrency would be
> > to do tpm_try_get_ops() before checking any flags. That way
> > tpm_hwrng_read() is guaranteed not conflict.
> > 
> > So the way I would fix this instead would be to (untested
> > wrote inline here):
> > 
> > int tpm_pm_suspend(struct device *dev)
> > {
> > 	struct tpm_chip *chip = dev_get_drvdata(dev);
> > 	int rc = 0;
> > 
> > 	if (!chip)
> > 		return -ENODEV;
> > 
> > 	rc = tpm_try_get_ops(chip);
> > 	if (rc) {
> > 		chip->flags = |= TPM_CHIP_FLAG_SUSPENDED;
> > 		return rc;
> > 	}
> > 
> > 	/* ... */
> > 
> > suspended:
> > 	chip->flags |= TPM_CHIP_FLAG_SUSPENDED;
> > 	tpm_put_ops(chip);
> > 
> > It does not really affect performance but guarantees that
> > tpm_hwrng_read() is guaranteed either fully finish or
> > never happens given that both sides take chip->lock.
> > 
> > So I'll put one more round of this and then this should be
> > stable and fully fixed.
> > 
> > BR, Jarkko
>
> Ah, yeah better to set it while it has the mutex. That should still be
> 'if (!rc)' after the tpm_try_get_ops() right? (I'm assuming that is just
> a transcription error).

Can you check v2 of the patch? It misses the tpm_hwrng_read() change
that you suggested. I think rc is checked there correctly but it is
always possible that I overlook/ignore something...

So no tags for that since an update is still coming but just the
parts that are already in it make sense.

>
> Regards,
> Jerry

BR, Jarkko