[PATCH v2 1/7] ima: refactor ima_dump_measurement_list to move memory allocation to a separate function

[Mimi Zohar]

Hi Tushar,

According to Documentation/process/submitting-patches.rst, the subject
line should be between 70-75 characters.

Perhaps something like "ima: define and call ima_alloc_kexec_buffer()".

On Thu, 2023-10-05 at 11:25 -0700, Tushar Sugandhi wrote:
> IMA allocates memory and dumps the measurement during kexec soft reboot
> as a single function call ima_dump_measurement_list().  It gets called
> during kexec 'load' operation.  It results in the IMA measurements
> between the window of kexec 'load' and 'execute' getting dropped when the
> system boots into the new Kernel.  One of the kexec requirements is the
> segment size cannot change between the 'load' and the 'execute'.
> Therefore, to address this problem, ima_dump_measurement_list() needs
> to be refactored to allocate the memory at kexec 'load', and dump the
> measurements at kexec 'execute'.  The function that allocates the memory
> should handle the scenario where the kexec load is called multiple times

The above pragraph is unnecessary.

> Refactor ima_dump_measurement_list() to move the memory allocation part
> to a separate function ima_alloc_kexec_buf() to allocate buffer of size
> 'kexec_segment_size' at kexec 'load'.  Make the local variables in
> function ima_dump_measurement_list() global, so that they can be accessed
> from ima_alloc_kexec_buf().  Make necessary changes to the function
> ima_add_kexec_buffer() to call the above two functions.

Fix the wording based on the suggested changes below.

> Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>

Before re-posting this patch set, verify there aren't any
"checkpatch.pl --strict" issues.
After applying each patch, compile the kernel and verify it still
works.

> ---
>  security/integrity/ima/ima_kexec.c | 126 +++++++++++++++++++++--------
>  1 file changed, 93 insertions(+), 33 deletions(-)
> 
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index 419dc405c831..307e07991865 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -15,61 +15,114 @@
>  #include "ima.h"
>  
>  #ifdef CONFIG_IMA_KEXEC
> +struct seq_file ima_kexec_file;

Define "ima_kexec_file" as static since it only used in this file.  
Since the variable does not need to be global, is there still a reason
for changing its name?   Minimize code change.

> +struct ima_kexec_hdr ima_khdr;
> +
> +void ima_clear_kexec_file(void)

The opposite of "set" is "clear" (e.g. set_git, clear_bit).  The
opposite of "alloc" would be "free" (e.g. ima_alloc_kexec_buf,
ima_free_kexec_buf)

> +{
> +	vfree(ima_kexec_file.buf);
> +	ima_kexec_file.buf = NULL;
> +	ima_kexec_file.size = 0;
> +	ima_kexec_file.read_pos = 0;
> +	ima_kexec_file.count = 0;
> +}
> +
> +static int ima_alloc_kexec_buf(size_t kexec_segment_size)
> +{
> +	if ((kexec_segment_size == 0) ||
> +	    (kexec_segment_size == ULONG_MAX) ||
> +	    ((kexec_segment_size >> PAGE_SHIFT) > totalram_pages() / 2)) {
> +		pr_err("%s: Invalid segment size for kexec: %zu\n",
> +			__func__, kexec_segment_size);
> +		return -EINVAL;
> +	}

Please avoid code duplication.  If moving the test here, then remove it
from its original place.

> +
> +	/*
> +	 * If kexec load was called before, clear the existing buffer
> +	 * before allocating a new one
> +	 */

> +	if (ima_kexec_file.buf)
> +		ima_clear_kexec_file();

Perhaps instead of always freeing the buffer, check and see whether the
size has changed.  If it hasn't changed, then simply return.  If it has
changed, perhaps use realloc().  Possible wording:

"Kexec may be called multiple times.  Free and re-alloc the buffer if
the size changed."

> +
> +	/* segment size can't change between kexec load and execute */
> +	ima_kexec_file.buf = vmalloc(kexec_segment_size);
> +	if (!ima_kexec_file.buf) {
> +		pr_err("%s: No memory for ima kexec measurement buffer\n",
> +			__func__);
> +		return -ENOMEM;
> +	}
> +
> +	ima_kexec_file.size = kexec_segment_size;
> +	ima_kexec_file.read_pos = 0;
> +	ima_kexec_file.count = sizeof(ima_khdr);	/* reserved space */
> +
> +	memset(&ima_khdr, 0, sizeof(ima_khdr));
> +	ima_khdr.version = 1;
> +
> +	return 0;
> +}
> +
>  static int ima_dump_measurement_list(unsigned long *buffer_size, void **buffer,
>  				     unsigned long segment_size)
>  {
>  	struct ima_queue_entry *qe;
> -	struct seq_file file;
> -	struct ima_kexec_hdr khdr;
>  	int ret = 0;
>  
> -	/* segment size can't change between kexec load and execute */
> -	file.buf = vmalloc(segment_size);
> -	if (!file.buf) {
> -		ret = -ENOMEM;
> -		goto out;
> +	if (!ima_kexec_file.buf) {
> +		pr_err("%s: Kexec file buf not allocated\n",
> +			__func__);
> +		return -EINVAL;
>  	}
>  
> -	file.size = segment_size;
> -	file.read_pos = 0;
> -	file.count = sizeof(khdr);	/* reserved space */
> +	/*
> +	 * Ensure the kexec buffer is large enough to hold ima_khdr
> +	 */
> +	if (ima_kexec_file.size < sizeof(ima_khdr)) {
> +		pr_err("%s: Kexec buffer size too low to hold ima_khdr\n",
> +			__func__);
> +		ima_clear_kexec_file();
> +		return -ENOMEM;
> +	}

Is this necessary?
 
> -	memset(&khdr, 0, sizeof(khdr));
> -	khdr.version = 1;
> +	/*
> +	 * If we reach here, then there is enough memory
> +	 * of size kexec_segment_size in ima_kexec_file.buf
> +	 * to copy at least partial IMA log.
> +	 * Make best effort to copy as many IMA measurements
> +	 * as possible.
> +	 */

Suggestion:

/* Copy as many IMA measurements list records as possible */

>  	list_for_each_entry_rcu(qe, &ima_measurements, later) {
> -		if (file.count < file.size) {
> -			khdr.count++;
> -			ima_measurements_show(&file, qe);
> +		if (ima_kexec_file.count < ima_kexec_file.size) {
> +			ima_khdr.count++;
> +			ima_measurements_show(&ima_kexec_file, qe);
>  		} else {
> -			ret = -EINVAL;
> +			ret = EFBIG;
> +			pr_err("%s: IMA log file is too big for Kexec buf\n",
> +				__func__);
>  			break;
>  		}
>  	}
>  
> -	if (ret < 0)
> -		goto out;
> -
>  	/*
>  	 * fill in reserved space with some buffer details
>  	 * (eg. version, buffer size, number of measurements)
>  	 */
> -	khdr.buffer_size = file.count;
> +	ima_khdr.buffer_size = ima_kexec_file.count;
>  	if (ima_canonical_fmt) {
> -		khdr.version = cpu_to_le16(khdr.version);
> -		khdr.count = cpu_to_le64(khdr.count);
> -		khdr.buffer_size = cpu_to_le64(khdr.buffer_size);
> +		ima_khdr.version = cpu_to_le16(ima_khdr.version);
> +		ima_khdr.count = cpu_to_le64(ima_khdr.count);
> +		ima_khdr.buffer_size = cpu_to_le64(ima_khdr.buffer_size);
>  	}
> -	memcpy(file.buf, &khdr, sizeof(khdr));
> +	memcpy(ima_kexec_file.buf, &ima_khdr, sizeof(ima_khdr));
>  
>  	print_hex_dump_debug("ima dump: ", DUMP_PREFIX_NONE, 16, 1,
> -			     file.buf, file.count < 100 ? file.count : 100,
> +			     ima_kexec_file.buf, ima_kexec_file.count < 100 ?
> +			     ima_kexec_file.count : 100,
>  			     true);
>  
> -	*buffer_size = file.count;
> -	*buffer = file.buf;
> -out:
> -	if (ret == -EINVAL)
> -		vfree(file.buf);
> +	*buffer_size = ima_kexec_file.count;
> +	*buffer = ima_kexec_file.buf;
> +
>  	return ret;
>  }

-- 
thanks,

Mimi