linux-kernel - Re: [PATCH v12 2/9] ima: define and call ima_alloc_kexec_file

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Message-ID: <aAHWFjfQgDBq84lH@MiWiFi-R3L-srv>
Date: Fri, 18 Apr 2025 12:33:26 +0800
From: Baoquan He <bhe@...hat.com>
To: steven chen <chenste@...ux.microsoft.com>
Cc: zohar@...ux.ibm.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,
	madvenka@...ux.microsoft.com, nramas@...ux.microsoft.com,
	James.Bottomley@...senpartnership.com, vgoyal@...hat.com,
	dyoung@...hat.com
Subject: Re: [PATCH v12 2/9] ima: define and call ima_alloc_kexec_file_buf()

Hi Steven,

On 04/15/25 at 07:10pm, steven chen wrote:
> From: Steven Chen <chenste@...ux.microsoft.com>
> 
> In the current implementation, the ima_dump_measurement_list() API is 
> called during the kexec "load" phase, where a buffer is allocated and 
> the measurement records are copied. Due to this, new events added after
> kexec load but before kexec execute are not carried over to the new kernel
> during kexec operation
> 
> Carrying the IMA measurement list across kexec requires allocating a
> buffer and copying the measurement records.  Separate allocating the
> buffer and copying the measurement records into separate functions in
> order to allocate the buffer at kexec 'load' and copy the measurements
> at kexec 'execute'.

Seems you didn't add note in this patch log to mention that the IMA
measurement list fails to verify when doing two consecuritv "kexec -s -l"
with/without a "kexec -s -u" in between. When people do bisecting and
come to this patch, she/he will see the failure even though it's not a
fatal blocker.

====
After moving the vfree() here at this stage in the patch set, the IMA
measurement list fails to verify when doing two consecutive "kexec -s -l"
with/without a "kexec -s -u" in between.  Only after "ima: kexec: move IMA log
copy from kexec load to execute" the IMA measurement list verifies properly with
the vfree() here.
====


> 
> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
> Signed-off-by: Steven Chen <chenste@...ux.microsoft.com>
> ---
>  security/integrity/ima/ima_kexec.c | 46 +++++++++++++++++++++++-------
>  1 file changed, 35 insertions(+), 11 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index 650beb74346c..b12ac3619b8f 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -15,26 +15,46 @@
>  #include "ima.h"
>  
>  #ifdef CONFIG_IMA_KEXEC
> +static struct seq_file ima_kexec_file;
> +
> +static void ima_free_kexec_file_buf(struct seq_file *sf)
> +{
> +	vfree(sf->buf);
> +	sf->buf = NULL;
> +	sf->size = 0;
> +	sf->read_pos = 0;
> +	sf->count = 0;
> +}
> +
> +static int ima_alloc_kexec_file_buf(size_t segment_size)
> +{
> +	ima_free_kexec_file_buf(&ima_kexec_file);
> +
> +	/* segment size can't change between kexec load and execute */
> +	ima_kexec_file.buf = vmalloc(segment_size);
> +	if (!ima_kexec_file.buf)
> +		return -ENOMEM;
> +
> +	ima_kexec_file.size = segment_size;
> +	ima_kexec_file.read_pos = 0;
> +	ima_kexec_file.count = sizeof(struct ima_kexec_hdr);	/* reserved space */
> +
> +	return 0;
> +}
> +
>  static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>  				     unsigned long segment_size)
>  {
> -	struct seq_file ima_kexec_file;
>  	struct ima_queue_entry *qe;
>  	struct ima_kexec_hdr khdr;
>  	int ret = 0;
>  
>  	/* segment size can't change between kexec load and execute */
> -	ima_kexec_file.buf = vmalloc(segment_size);
>  	if (!ima_kexec_file.buf) {
> -		ret = -ENOMEM;
> -		goto out;
> +		pr_err("Kexec file buf not allocated\n");
> +		return -EINVAL;
>  	}
>  
> -	ima_kexec_file.file = NULL;
> -	ima_kexec_file.size = segment_size;
> -	ima_kexec_file.read_pos = 0;
> -	ima_kexec_file.count = sizeof(khdr);	/* reserved space */
> -
>  	memset(&khdr, 0, sizeof(khdr));
>  	khdr.version = 1;
>  	/* This is an append-only list, no need to hold the RCU read lock */
> @@ -71,8 +91,6 @@ static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>  	*buffer_size = ima_kexec_file.count;
>  	*buffer = ima_kexec_file.buf;
>  out:
> -	if (ret == -EINVAL)
> -		vfree(ima_kexec_file.buf);
>  	return ret;
>  }
>  
> @@ -111,6 +129,12 @@ void ima_add_kexec_buffer(struct kimage *image)
>  		return;
>  	}
>  
> +	ret = ima_alloc_kexec_file_buf(kexec_segment_size);
> +	if (ret < 0) {
> +		pr_err("Not enough memory for the kexec measurement buffer.\n");
> +		return;
> +	}
> +
>  	ima_dump_measurement_list(&kexec_buffer_size, &kexec_buffer,
>  				  kexec_segment_size);
>  	if (!kexec_buffer) {
> -- 
> 2.43.0
>