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Date: Mon, 23 Mar 2026 07:21:28 +0200
From: Jarkko Sakkinen <jarkko@kernel.org>
To: Nayna Jain <nayna@linux.ibm.com>
Cc: Srish Srinivasan <ssrish@linux.ibm.com>,
	linux-integrity@vger.kernel.org, keyrings@vger.kernel.org,
	James.Bottomley@hansenpartnership.com, zohar@linux.ibm.com,
	stefanb@linux.ibm.com, linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org
Subject: Re: [PATCH v2 1/2] keys/trusted_keys: clean up debug message logging
 in the tpm backend
Message-ID: <acDN2OIQcWgjk1g6@kernel.org>
References: <20260220183426.80446-1-ssrish@linux.ibm.com>
 <20260220183426.80446-2-ssrish@linux.ibm.com>
 <7f8b8478-5cd8-4d97-bfd0-341fd5cf10f9@linux.ibm.com>
 <acDM-hNRThVPRYhq@kernel.org>
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In-Reply-To: <acDM-hNRThVPRYhq@kernel.org>

On Mon, Mar 23, 2026 at 07:17:51AM +0200, Jarkko Sakkinen wrote:
> On Mon, Mar 09, 2026 at 06:45:23PM -0400, Nayna Jain wrote:
> > 
> > On 2/20/26 1:34 PM, Srish Srinivasan wrote:
> > > The TPM trusted-keys backend uses a local TPM_DEBUG guard and pr_info()
> > > for logging debug information.
> > > 
> > > Replace pr_info() with pr_debug(), and use KERN_DEBUG for print_hex_dump().
> > > Remove TPM_DEBUG.
> > > 
> > > No functional change intended.
> > There is functional change here.  This change allows secret and nonce in the
> > function dump_sess() to be logged to kernel logs when dynamic debug is
> > enabled. Previously, it was possible only in the debug builds and not the
> > production builds at runtime. With this change, it is always there in
> > production build. This can result in possible attack.
> 
> Good catch, thank you. It's in my master branch still (not in -next).
> 
> TPM_DEBUG should be removed in all cases. If you really want to read
> a secret, use tracing tools.
> 
> This only proves that the print should exist or should be a constant
> value, or overwritten same length value.

I dropped the current patches but yeah, a comment "do not touch this,
could be poisonous" won't be an acceptable way to address this.

If you want "some" debug information you can always put F-string or
0-string of same length, so there's options.

BR, Jarkko