Re: [PATCH v5 7/8] ima: make the kexec extra memory configurable

[Mimi Zohar <zohar@linux.ibm.com>]

Hi Tushar,

On Wed, 2024-02-14 at 07:38 -0800, Tushar Sugandhi wrote:
> The extra memory allocated for carrying the IMA measurement list across
> kexec is hard-coded as half a PAGE.  Make it configurable.
> 
> Define a Kconfig option, IMA_KEXEC_EXTRA_MEMORY_KB, to configure the
> extra memory (in kb) to be allocated for IMA measurements added during
> kexec soft reboot.  Ensure the default value of the option is set such
> that extra half a page of memory for additional measurements is allocated
> for the additional measurements.
> 
> Update ima_add_kexec_buffer() function to allocate memory based on the
> Kconfig option value, rather than the currently hard-coded one.
> 
> Suggested-by: Stefan Berger <stefanb@linux.ibm.com>
> Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> ---
>  security/integrity/ima/Kconfig     |  9 +++++++++
>  security/integrity/ima/ima_kexec.c | 15 ++++++++++-----
>  2 files changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index b98bfe9efd0c..4c0fc53d6aa3 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -320,4 +320,13 @@ config IMA_DISABLE_HTABLE
>  	help
>  	   This option disables htable to allow measurement of duplicate
> records.
>  
> +config IMA_KEXEC_EXTRA_MEMORY_KB
> +	int
> +	depends on IMA_KEXEC
> +	default 0
> +	help
> +	  IMA_KEXEC_EXTRA_MEMORY_KB determines the extra memory to be
> +	  allocated (in kb) for IMA measurements added during kexec soft reboot.
> +	  If set to the default value, an extra half a page of memory for those
> +	  additional measurements will be allocated.
>  endif
> diff --git a/security/integrity/ima/ima_kexec.c
> b/security/integrity/ima/ima_kexec.c
> index dbeeb7f1355e..50903d4ce880 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -126,6 +126,7 @@ void ima_add_kexec_buffer(struct kimage *image)
>  				  .buf_min = 0, .buf_max = ULONG_MAX,
>  				  .top_down = true };
>  	unsigned long binary_runtime_size;
> +	unsigned long extra_size;
>  
>  	/* use more understandable variable names than defined in kbuf */
>  	void *kexec_buffer = NULL;
> @@ -133,15 +134,19 @@ void ima_add_kexec_buffer(struct kimage *image)
>  	int ret;
>  
>  	/*
> -	 * Reserve an extra half page of memory for additional measurements
> -	 * added during the kexec load.
> +	 * Reserve extra memory for measurements added during kexec.
>  	 */
> -	binary_runtime_size = ima_get_binary_runtime_size();
> +	if (CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB <= 0)
> +		extra_size = PAGE_SIZE / 2;
> +	else
> +		extra_size = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
> +	binary_runtime_size = ima_get_binary_runtime_size() + extra_size;

It's clearer if the 'extra_size' is added to the segment_size, not the
binary_runtime_size.  Please revert this change.

> +
>  	if (binary_runtime_size >= ULONG_MAX - PAGE_SIZE)
>  		kexec_segment_size = ULONG_MAX;
>  	else
> -		kexec_segment_size = ALIGN(ima_get_binary_runtime_size() +
> -					   PAGE_SIZE / 2, PAGE_SIZE);
> +		kexec_segment_size = ALIGN(binary_runtime_size, PAGE_SIZE);

Please replace binary_runtime_size with "ima_get_binary_runtime_size() +
extra_size".

Mimi

>  	if ((kexec_segment_size == ULONG_MAX) ||
>  	    ((kexec_segment_size >> PAGE_SHIFT) > totalram_pages() / 2)) {
>  		pr_err("Binary measurement list too large.\n");