Re: [PATCH v13 2/9] ima: define and call ima_alloc_kexec_file_buf()

[Stefan Berger <stefanb@linux.ibm.com>]

On 4/21/25 6:25 PM, steven chen wrote:
> From: Steven Chen <chenste@linux.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'.
> 
> 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.
> 
> Co-developed-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Signed-off-by: Steven Chen <chenste@linux.microsoft.com>
> Acked-by: Baoquan He <bhe@redhat.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) {

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>