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Message-ID: <1a06e28dbac24d32168a7362a903d6076fafdc34.camel@kernel.org>
Subject: Re: [PATCH v3 4/6] tpm: Support TPM2 sized buffers (TPM2B)
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     James Bottomley <James.Bottomley@HansenPartnership.com>,
        linux-integrity@vger.kernel.org
Cc:     keyrings@vger.kernel.org,
        William Roberts <bill.c.roberts@gmail.com>,
        Stefan Berger <stefanb@linux.ibm.com>,
        David Howells <dhowells@redhat.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Mimi Zohar <zohar@linux.ibm.com>,
        Peter Huewe <peterhuewe@gmx.de>,
        Paul Moore <paul@paul-moore.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Jerry Snitselaar <jsnitsel@redhat.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        Julien Gomes <julien@arista.com>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:SECURITY SUBSYSTEM" 
        <linux-security-module@vger.kernel.org>
Date:   Mon, 06 Nov 2023 05:25:15 +0200
In-Reply-To: <d4157726d924a3ddad477923d6bcb4a8e6a55e60.camel@HansenPartnership.com>
References: <20231024011531.442587-1-jarkko@kernel.org>
         <20231024011531.442587-5-jarkko@kernel.org>
         <d4157726d924a3ddad477923d6bcb4a8e6a55e60.camel@HansenPartnership.com>
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On Fri, 2023-10-27 at 08:32 -0400, James Bottomley wrote:
> On Tue, 2023-10-24 at 04:15 +0300, Jarkko Sakkinen wrote:
> > +++ b/drivers/char/tpm/tpm-buf.c
> > @@ -7,22 +7,32 @@
> > =C2=A0#include <linux/tpm.h>
> > =C2=A0
> > =C2=A0/**
> > - * tpm_buf_init() - Initialize from the heap
> > + * tpm_buf_init() - Initialize a TPM buffer
> > =C2=A0 * @buf:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0A @tpm_buf
> > + * @sized:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Represent a sized buffer (TPM2=
B)
> > + * @alloc:=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Allocate from the heap
> > =C2=A0 *
> > =C2=A0 * Initialize all structure fields to zero, allocate a page from =
the
> > heap, and
> > =C2=A0 * zero the bytes that the buffer headers will consume.
> > =C2=A0 *
> > =C2=A0 * Return: 0 or -ENOMEM
> > =C2=A0 */
> > -int tpm_buf_init(struct tpm_buf *buf)
> > +int tpm_buf_init(struct tpm_buf *buf, bool alloc, bool sized)
>=20
> I think it creates a phenomenally confusing interface to use multiple
> booleans because, unlike flags, it's not self describing at point of
> use.=C2=A0 The confusion is enormously heightened here by having the doc
> book arguments be the reverse of the actual function prototype (I just
> tripped over this).
>=20
> The alloc flag is particularly counter intuitive: if you pass in an
> allocated buffer, you expect to be responsible for freeing it again,
> but that's not how you use it; you really use it like a reset not an
> alloc, which looks odd because you already created a separate
> tpm_buf_reset function which can't be used in this case.
>=20
> Why not replace the alloc flags with two reset functions: one for TPM2B
> buffers and one for command buffers?
>=20
> James

Or you can make that as internal (__tpm_buf_init()) and add two
wrappers.

BR, Jarkko