linux-kernel - Re: [PATCH] tpm: Use -EPERM as fallback error code in tpm_ret_to

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Message-ID: <aNKwG2Q6AG3BNB2c@kernel.org>
Date: Tue, 23 Sep 2025 17:35:07 +0300
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: linux-integrity@...r.kernel.org,
	Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>,
	stable@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
	Jason Gunthorpe <jgg@...pe.ca>, David Howells <dhowells@...hat.com>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Mimi Zohar <zohar@...ux.ibm.com>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:KEYS/KEYRINGS" <keyrings@...r.kernel.org>,
	"open list:SECURITY SUBSYSTEM" <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH] tpm: Use -EPERM as fallback error code in tpm_ret_to_err

On Mon, Sep 22, 2025 at 11:25:42AM +0200, Stefano Garzarella wrote:
> On Mon, Sep 22, 2025 at 10:23:32AM +0300, Jarkko Sakkinen wrote:
> > From: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>
> > 
> > Using -EFAULT here was not the best idea for tpm_ret_to_err as the fallback
> > error code as it is no concise with trusted keys.
> > 
> > Change the fallback as -EPERM, process TPM_RC_HASH also in tpm_ret_to_err,
> > and by these changes make the helper applicable for trusted keys.
> > 
> > Cc: stable@...r.kernel.org # v6.15+
> > Fixes: 539fbab37881 ("tpm: Mask TPM RC in tpm2_start_auth_session()")
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>
> > ---
> > include/linux/tpm.h                       |  9 +++++---
> > security/keys/trusted-keys/trusted_tpm2.c | 26 ++++++-----------------
> > 2 files changed, 13 insertions(+), 22 deletions(-)
> > 
> > diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> > index dc0338a783f3..667d290789ca 100644
> > --- a/include/linux/tpm.h
> > +++ b/include/linux/tpm.h
> > @@ -449,13 +449,16 @@ static inline ssize_t tpm_ret_to_err(ssize_t ret)
> > 	if (ret < 0)
> > 		return ret;
> > 
> > -	switch (tpm2_rc_value(ret)) {
> > -	case TPM2_RC_SUCCESS:
> 
> I slightly prefer the `case TPM2_RC_SUCCESS` but I don't have a strong
> opinion.
> 
> > +	if (!ret)
> > 		return 0;
> 
> If we want to remove the `case TPM2_RC_SUCCESS`, can we just merge this
> condition with the if on top, I mean:
> 
> 	if (ret <= 0)
> 		return ret;

I can cope with this i.e. revert back, it's not really part of the scope
and was totally intentional

> 
> > +
> > +	switch (tpm2_rc_value(ret)) {
> > 	case TPM2_RC_SESSION_MEMORY:
> > 		return -ENOMEM;
> > +	case TPM2_RC_HASH:
> > +		return -EINVAL;
> > 	default:
> > -		return -EFAULT;
> > +		return -EPERM;
> > 	}
> > }
> > 
> > diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> > index 024be262702f..e165b117bbca 100644
> > --- a/security/keys/trusted-keys/trusted_tpm2.c
> > +++ b/security/keys/trusted-keys/trusted_tpm2.c
> > @@ -348,25 +348,19 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
> > 	}
> > 
> > 	blob_len = tpm2_key_encode(payload, options, &buf.data[offset], blob_len);
> > +	if (blob_len < 0)
> > +		rc = blob_len;
> > 
> > out:
> > 	tpm_buf_destroy(&sized);
> > 	tpm_buf_destroy(&buf);
> > 
> > -	if (rc > 0) {
> > -		if (tpm2_rc_value(rc) == TPM2_RC_HASH)
> > -			rc = -EINVAL;
> > -		else
> > -			rc = -EPERM;
> > -	}
> > -	if (blob_len < 0)
> 
> nit: since `blob_len` is not accessed anymore in the error path, can we
> avoid to set it to 0 when declaring it?
> 
> Thanks,
> Stefano
> 
> > -		rc = blob_len;
> > -	else
> > +	if (!rc)
> > 		payload->blob_len = blob_len;
> > 
> > out_put:
> > 	tpm_put_ops(chip);
> > -	return rc;
> > +	return tpm_ret_to_err(rc);
> > }
> > 
> > /**
> > @@ -468,10 +462,7 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
> > 		kfree(blob);
> > 	tpm_buf_destroy(&buf);
> > 
> > -	if (rc > 0)
> > -		rc = -EPERM;
> > -
> > -	return rc;
> > +	return tpm_ret_to_err(rc);
> > }
> > 
> > /**
> > @@ -534,8 +525,6 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
> > 	tpm_buf_fill_hmac_session(chip, &buf);
> > 	rc = tpm_transmit_cmd(chip, &buf, 6, "unsealing");
> > 	rc = tpm_buf_check_hmac_response(chip, &buf, rc);
> > -	if (rc > 0)
> > -		rc = -EPERM;
> > 
> > 	if (!rc) {
> > 		data_len = be16_to_cpup(
> > @@ -568,7 +557,7 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
> > 
> > out:
> > 	tpm_buf_destroy(&buf);
> > -	return rc;
> > +	return tpm_ret_to_err(rc);
> > }
> > 
> > /**
> > @@ -600,6 +589,5 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
> > 
> > out:
> > 	tpm_put_ops(chip);
> > -
> > -	return rc;
> > +	return tpm_ret_to_err(rc);
> > }
> > -- 
> > 2.39.5
> > 
> 

BR, Jarkko