linux-kernel - Re: [PATCH v7 7/7] ima: measure kexec load and exec events as critical data

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Message-ID: <8ca0bdd9-7cae-4adf-b4c0-eebf057d4c5b@linux.ibm.com>
Date: Fri, 7 Feb 2025 12:48:52 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: Mimi Zohar <zohar@...ux.ibm.com>,
        steven chen <chenste@...ux.microsoft.com>,
        roberto.sassu@...weicloud.com, roberto.sassu@...wei.com,
        eric.snowberg@...cle.com, ebiederm@...ssion.com, paul@...l-moore.com,
        code@...icks.com, bauermann@...abnow.com,
        linux-integrity@...r.kernel.org, kexec@...ts.infradead.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: madvenka@...ux.microsoft.com, nramas@...ux.microsoft.com,
        James.Bottomley@...senPartnership.com
Subject: Re: [PATCH v7 7/7] ima: measure kexec load and exec events as
 critical data



On 2/7/25 12:06 PM, Mimi Zohar wrote:
> On Fri, 2025-02-07 at 10:16 -0500, Mimi Zohar wrote:
>> On Mon, 2025-02-03 at 15:20 -0800, steven chen wrote:
>>> The amount of memory allocated at kexec load, even with the extra memory
>>> allocated, might not be large enough for the entire measurement list.  The
>>> indeterminate interval between kexec 'load' and 'execute' could exacerbate
>>> this problem.
>>>
>>> Define two new IMA events, 'kexec_load' and 'kexec_execute', to be
>>> measured as critical data at kexec 'load' and 'execute' respectively.
>>> Report the allocated kexec segment size, IMA binary log size and the
>>> runtime measurements count as part of those events.
>>>
>>> These events, and the values reported through them, serve as markers in
>>> the IMA log to verify the IMA events are captured during kexec soft
>>> reboot.  The presence of a 'kexec_load' event in between the last two
>>> 'boot_aggregate' events in the IMA log implies this is a kexec soft
>>> reboot, and not a cold-boot. And the absence of 'kexec_execute' event
>>> after kexec soft reboot implies missing events in that window which
>>> results in inconsistency with TPM PCR quotes, necessitating a cold boot
>>> for a successful remote attestation.
>>
>> As a reminder, please include directions for verifying the buffer data hash against
>> the buffer data.  The directions would be similar to those in commit 6b4da8c0e7f
>> ("IMA: Define a new template field buf").
>>
>>>
>>> Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
>>> Author: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>>> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>>> Signed-off-by: steven chen <chenste@...ux.microsoft.com>
>>> ---
>>>   security/integrity/ima/ima_kexec.c | 23 +++++++++++++++++++++++
>>>   1 file changed, 23 insertions(+)
>>>
>>> diff --git a/security/integrity/ima/ima_kexec.c
>>> b/security/integrity/ima/ima_kexec.c
>>> index c9c916f69ca7..0342ddfa9342 100644
>>> --- a/security/integrity/ima/ima_kexec.c
>>> +++ b/security/integrity/ima/ima_kexec.c
>>> @@ -17,6 +17,8 @@
>>>   #include "ima.h"
>>>   
>>>   #ifdef CONFIG_IMA_KEXEC
>>> +#define IMA_KEXEC_EVENT_LEN 256
>>> +
>>>   static struct seq_file ima_kexec_file;
>>>   static void *ima_kexec_buffer;
>>>   static size_t kexec_segment_size;
>>> @@ -36,6 +38,24 @@ static void ima_free_kexec_file_buf(struct seq_file *sf)
>>>   	ima_reset_kexec_file(sf);
>>>   }
>>>   
>>> +static void ima_measure_kexec_event(const char *event_name)
>>> +{
>>> +	char ima_kexec_event[IMA_KEXEC_EVENT_LEN];
>>> +	size_t buf_size = 0;
>>> +	long len;
>>> +
>>> +	buf_size = ima_get_binary_runtime_size();
>>> +	len = atomic_long_read(&ima_htable.len);
>>> +
>>> +	scnprintf(ima_kexec_event, IMA_KEXEC_EVENT_LEN,
>>> +			"kexec_segment_size=%lu;ima_binary_runtime_size=%lu;"
>>> +			"ima_runtime_measurements_count=%ld;",
>>> +				kexec_segment_size, buf_size, len);
>>
>>  From scripts/checkpatch.pl, "Alignment should match open parenthesis".
>>
>>> +
>>> +	ima_measure_critical_data("ima_kexec", event_name, ima_kexec_event,
>>> +					strlen(ima_kexec_event), false, NULL,
>>> 0);
>>
>>  From the kernel-doc scnprintf(), returns the number of bytes.  There should be no
>> need to calculate it using strlen().
>>
>>> +}
>>> +
>>>   static int ima_alloc_kexec_file_buf(size_t segment_size)
>>>   {
>>>   	/*
>>> @@ -60,6 +80,7 @@ static int ima_alloc_kexec_file_buf(size_t segment_size)
>>>   out:
>>>   	ima_kexec_file.read_pos = 0;
>>>   	ima_kexec_file.count = sizeof(struct ima_kexec_hdr);	/* reserved
>>> space
>>> */
>>> +	ima_measure_kexec_event("kexec_load");
>>>   
>>>   	return 0;
>>>   }
>>> @@ -201,6 +222,8 @@ static int ima_update_kexec_buffer(struct notifier_block
>>> *self,
>>>   		return ret;
>>>   	}
>>>   
>>> +	ima_measure_kexec_event("kexec_execute");
>>> +
>>>   	ret = ima_dump_measurement_list(&buf_size, &buf,
>>>   					kexec_segment_size);
>>>   
>>
>> After fixing up and applying this patch set to 6.14.0-rc1, I'm not seeing the
>> "kexec_execute".  Even after changing the default extra memory, I'm still not
>> seeing
>> the measurement.
> 
> FYI, after reverting commit 254ef9541d68 ("ima: Suspend PCR extends and log appends
> when rebooting"), I'm seeing the "kexec_execute" measurement.

I would try sth. like this:
static int ima_reboot_notifier(struct notifier_block *nb,
			       unsigned long action,
			       void *data)
{
	if (action == SYS_RESTART && data && !strcmp(data, "kexec reboot"))
		ima_measure_kexec_event("kexec_execute");
> 
> Mimi
> 
>