linux-kernel - Re: [PATCH v4] tpm: Managed allocations for tpm

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Message-ID: <7316e17a4d8dba36a4a773f87dc4f516697dd402.camel@HansenPartnership.com>
Date: Tue, 01 Jul 2025 22:51:55 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, linux-kernel@...r.kernel.org
Cc: keyrings@...r.kernel.org, Stefan Berger <stefanb@...ux.ibm.com>, Jarkko
 Sakkinen <jarkko.sakkinen@...nsys.com>, Peter Huewe <peterhuewe@....de>,
 Jason Gunthorpe <jgg@...pe.ca>, Mimi Zohar <zohar@...ux.ibm.com>, David
 Howells <dhowells@...hat.com>, Paul Moore <paul@...l-moore.com>, James
 Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, "open
 list:TPM DEVICE DRIVER" <linux-integrity@...r.kernel.org>, "open
 list:SECURITY SUBSYSTEM" <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v4] tpm: Managed allocations for tpm_buf instances

On Tue, 2025-07-01 at 17:51 +0300, Jarkko Sakkinen wrote:
> Repeal and replace tpm_buf_init() and tpm_buf_init_sized() with
> tpm_buf_alloc(), which returns a buffer of  memory with the struct
> tpm_buf header at the beginning of the returned buffer. This leaves
> 4090 bytes of free space for the payload.

Shouldn't this be accounted for in tpm_buf_append()? right now it will
let us run off the end of the allocation by six bytes before it signals
overflow because it's checking final length against PAGE_SIZE not
PAGE_SIZE - sizeof(struct tpm_buf).  I realise this should be an
impossible condition in production, but it's useful for debugging so we
should be accurate about it to avoid hard to detect bugs.

Regards,

James