Re: [PATCH 06/10] ima: update buffer at kexec execute with ima measurements

From: Mimi Zohar <zohar@linux.ibm.com>
To: Tushar Sugandhi <tusharsu@linux.microsoft.com>,
	noodles@fb.com, bauermann@kolabnow.com,
	kexec@lists.infradead.org, linux-integrity@vger.kernel.org
Cc: code@tyhicks.com, nramas@linux.microsoft.com,
	paul@paul-moore.com, Eric Biederman <ebiederm@xmission.com>
Subject: Re: [PATCH 06/10] ima: update buffer at kexec execute with ima measurements
Date: Wed, 12 Jul 2023 11:45:08 -0400	[thread overview]
Message-ID: <0adc4f1754dcbb0412603f48c18bebb25a6cd2a8.camel@linux.ibm.com> (raw)
In-Reply-To: <9b7db004-0517-9163-e9d5-9555b416144c@linux.microsoft.com>

On Tue, 2023-07-11 at 12:08 -0700, Tushar Sugandhi wrote:
> Adding Eric to cc.
> 
> On 7/7/23 12:49, Mimi Zohar wrote:
> > On Fri, 2023-07-07 at 11:01 -0400, Mimi Zohar wrote:
> >> Hi Tushar,
> >>
> >> On Mon, 2023-07-03 at 14:57 -0700, Tushar Sugandhi wrote:
> >>
> >>> +/*
> >>> + * Called during kexec execute so that IMA can update the measurement list.
> >>> + */
> >>> +static int ima_update_kexec_buffer(struct notifier_block *self,
> >>> +				   unsigned long action, void *data)
> >>> +{
> >>> +	void *new_buffer = NULL;
> >>> +	size_t new_buffer_size, cur_buffer_size;
> >>> +	bool resume = false;
> >>> +
> >>> +	if (!kexec_in_progress) {
> >>> +		pr_info("%s: No kexec in progress.\n", __func__);
> >>> +		return NOTIFY_OK;
> >>> +	}
> >>> +
> >>> +	if (!ima_kexec_buffer) {
> >>> +		pr_err("%s: Kexec buffer not set.\n", __func__);
> >>> +		return NOTIFY_OK;
> >>> +	}
> >>> +
> >>> +	ima_measurements_suspend();
> >>> +
> >>> +	cur_buffer_size = kexec_segment_size - sizeof(struct ima_kexec_hdr);
> >>> +	new_buffer_size = ima_get_binary_runtime_size();
> >>> +	if (new_buffer_size > cur_buffer_size) {
> >>> +		pr_err("%s: Measurement list grew too large.\n", __func__);
> >>> +		resume = true;
> >>> +		goto out;
> >>> +	}
> >> This changes the current behavior of carrying as many measurements
> >> across kexec as possible.  True the measurement list won't verify
> >> against the TPM PCRs, but not copying the measurements leaves the
> >> impression there weren't any previous measurements.
> >>
> >> This also explains the reason for allocating an IMA buffer (patch 1/10)
> >> and not writing the measurements directly into the kexec buffer.
> > If not carrying even a partial measurement list across kexec is
> > desired, then in addition to the "boot_aggregate" record, define a new
> > record containing the TPM pcrcounter.  With this information,
> > attestation servers will at least be able to detect if the measurement
> > list was truncated.

> Sure.  Recording TPM pcrcounter at boot aggregate and
> Kexec 'load' should provide the necessary information to the
> attestation servers.  We can implement this if needed, based on how
> rest of the series evolves.

Recording the TPM pcrcounter should be done independently of this patch
set.  This patch set would have a dependency on it.

-- 
thanks,

Mimi

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