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