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

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Message-ID: <b2b3fa5d3d20284f790ce74bb97da2b9795a0e0e.camel@linux.ibm.com>
Date: Fri, 07 Feb 2025 12:06:11 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: steven chen <chenste@...ux.microsoft.com>, stefanb@...ux.ibm.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 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.

Mimi