Re: [PATCH v10 2/8] ima: define and call ima_alloc_kexec_file_buf()

[Baoquan He <bhe@redhat.com>]

On 03/17/25 at 06:04pm, steven chen wrote:
> 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'.
> 
> This patch includes the following changes:
>  - Refactor ima_dump_measurement_list() to move the memory allocation
>    to a separate function ima_alloc_kexec_file_buf() which allocates
>    buffer of size 'kexec_segment_size' at kexec 'load'.
>  - Make the local variable ima_kexec_file in ima_dump_measurement_list()
>    a local static to the file, so that it can be accessed from 
>    ima_alloc_kexec_file_buf().
>  - Make necessary changes to the function ima_add_kexec_buffer() to call
>    the above two functions.

We may not need above details about code change because it's not so
difficult to get them from patch.

> 
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Signed-off-by: steven chen <chenste@linux.microsoft.com>
> ---
>  security/integrity/ima/ima_kexec.c | 67 +++++++++++++++++++++++++-----
>  1 file changed, 56 insertions(+), 11 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index 8567619889d1..45170e283272 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -15,6 +15,48 @@
>  #include "ima.h"
>  
>  #ifdef CONFIG_IMA_KEXEC
> +static struct seq_file ima_kexec_file;
> +
> +static void ima_reset_kexec_file(struct seq_file *sf)
> +{
> +	sf->buf = NULL;
> +	sf->size = 0;
> +	sf->read_pos = 0;
> +	sf->count = 0;
> +}
> +
> +static void ima_free_kexec_file_buf(struct seq_file *sf)
> +{
> +	vfree(sf->buf);
> +	ima_reset_kexec_file(sf);
> +}
> +
> +static int ima_alloc_kexec_file_buf(size_t segment_size)
> +{
> +	/*
> +	 * kexec 'load' may be called multiple times.
> +	 * Free and realloc the buffer only if the segment_size is
> +	 * changed from the previous kexec 'load' call.
> +	 */
> +	if (ima_kexec_file.buf && ima_kexec_file.size == segment_size)
> +		goto out;
> +
> +	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;
> +
> +out:
> +	ima_kexec_file.read_pos = 0;
> +	ima_kexec_file.count = sizeof(struct ima_kexec_hdr);	/* reserved space */
> +
> +	return 0;
> +}
> +
>  /*
>   * Copy the measurement list to the allocated memory
>   * compare the size of IMA measurement list with the size of the allocated memory
> @@ -26,23 +68,16 @@
>  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 */
> @@ -79,8 +114,6 @@ 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;
>  }
>  
> @@ -119,6 +152,12 @@ 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) {
> @@ -140,6 +179,12 @@ void ima_add_kexec_buffer(struct kimage *image)
>  	image->ima_buffer_size = kexec_segment_size;
>  	image->ima_buffer = kexec_buffer;
>  
> +	/*
> +	 * kexec owns kexec_buffer after kexec_add_buffer() is called
> +	 * and it will vfree() that buffer.
> +	 */
> +	ima_reset_kexec_file(&ima_kexec_file);

I can't see why we need call ima_reset_kexec_file() here. If we need
reuse the buffer, we will reset the needed fields at the end of
ima_alloc_kexec_file_buf(). Not sure if I miss anything.

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 */

        return 0;
}