linux-kernel - Re: [PATCH v3] tpm: Lock TPM chip in tpm_pm

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Message-ID: <ke4tjq5p43g7z3dy4wowagwsf6tzfhecexkdmgkizvqu6n5tvl@op3zhjmplntw>
Date: Fri, 1 Nov 2024 13:23:09 -0700
From: Jerry Snitselaar <jsnitsel@...hat.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>, 
	stable@...r.kernel.org, Mike Seo <mikeseohyungjin@...il.com>, 
	"open list:TPM DEVICE DRIVER" <linux-integrity@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: 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@...r.kernel.org # v6.4+
> Fixes: 99d464506255 ("tpm: Prevent hwrng from activating during resume")
> Reported-by: Mike Seo <mikeseohyungjin@...il.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219383
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.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
>