linux-kernel - Re: [PATCH v11 16/20] tpm: Make locality requests return consistent values

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Message-Id: <D5AR9TGFZL14.AZMGA2G8GTDA@kernel.org>
Date: Fri, 01 Nov 2024 12:04:41 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Ross Philipson" <ross.philipson@...cle.com>,
 <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
 <linux-integrity@...r.kernel.org>, <linux-doc@...r.kernel.org>,
 <linux-crypto@...r.kernel.org>, <kexec@...ts.infradead.org>,
 <linux-efi@...r.kernel.org>, <iommu@...ts.linux-foundation.org>
Cc: <dpsmith@...rtussolutions.com>, <tglx@...utronix.de>,
 <mingo@...hat.com>, <bp@...en8.de>, <hpa@...or.com>,
 <dave.hansen@...ux.intel.com>, <ardb@...nel.org>, <mjg59@...f.ucam.org>,
 <James.Bottomley@...senpartnership.com>, <peterhuewe@....de>,
 <jgg@...pe.ca>, <luto@...capital.net>, <nivedita@...m.mit.edu>,
 <herbert@...dor.apana.org.au>, <davem@...emloft.net>, <corbet@....net>,
 <ebiederm@...ssion.com>, <dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>,
 <kanth.ghatraju@...cle.com>, <andrew.cooper3@...rix.com>,
 <trenchboot-devel@...glegroups.com>
Subject: Re: [PATCH v11 16/20] tpm: Make locality requests return consistent
 values

On Fri Sep 13, 2024 at 11:05 PM EEST, Ross Philipson wrote:
> From: "Daniel P. Smith" <dpsmith@...rtussolutions.com>
>
> The function tpm_tis_request_locality() is expected to return the locality
> value that was requested, or a negative error code upon failure. If it is called
> while locality_count of struct tis_data is non-zero, no actual locality request
> will be sent. Because the ret variable is initially set to 0, the
> locality_count will still get increased, and the function will return 0. For a
> caller, this would indicate that locality 0 was successfully requested and not
> the state changes just mentioned.
>
> Additionally, the function __tpm_tis_request_locality() provides inconsistent
> error codes. It will provide either a failed IO write or a -1 should it have
> timed out waiting for locality request to succeed.
>
> This commit changes __tpm_tis_request_locality() to return valid negative error
> codes to reflect the reason it fails. It then adjusts the return value check in
> tpm_tis_request_locality() to check for a non-negative return value before
> incrementing locality_cout. In addition, the initial value of the ret value is
> set to a negative error to ensure the check does not pass if
> __tpm_tis_request_locality() is not called.
>
> Signed-off-by: Daniel P. Smith <dpsmith@...rtussolutions.com>
> Signed-off-by: Ross Philipson <ross.philipson@...cle.com>
> ---
>  drivers/char/tpm/tpm_tis_core.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 22ebf679ea69..20a8b341be0d 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -210,7 +210,7 @@ static int __tpm_tis_request_locality(struct tpm_chip *chip, int l)
>  again:
>  		timeout = stop - jiffies;
>  		if ((long)timeout <= 0)
> -			return -1;
> +			return -EBUSY;
>  		rc = wait_event_interruptible_timeout(priv->int_queue,
>  						      (check_locality
>  						       (chip, l)),
> @@ -229,18 +229,21 @@ static int __tpm_tis_request_locality(struct tpm_chip *chip, int l)
>  			tpm_msleep(TPM_TIMEOUT);
>  		} while (time_before(jiffies, stop));
>  	}
> -	return -1;
> +	return -EBUSY;
>  }
>  
>  static int tpm_tis_request_locality(struct tpm_chip *chip, int l)
>  {
>  	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> -	int ret = 0;
> +	int ret = -EBUSY;
> +
> +	if (l < 0 || l > TPM_MAX_LOCALITY)
> +		return -EINVAL;
>  
>  	mutex_lock(&priv->locality_count_mutex);
>  	if (priv->locality_count == 0)
>  		ret = __tpm_tis_request_locality(chip, l);
> -	if (!ret)
> +	if (ret >= 0)
>  		priv->locality_count++;
>  	mutex_unlock(&priv->locality_count_mutex);
>  	return ret;

First of all, -1 is as consistent value as a value can be.

Secondly:

	if (tpm_tis_request_locality(chip, 0) != 0)
		return -EBUSY;

What am I missing here?

BR, Jarkko