[PATCH v3 6/7] ima: configure memory to log events between kexec load and execute

[Mimi Zohar]

Hi Tushar,

The Subject line should include the word "extra".   The use of the
extra memory isn't limited to the measurements between the kexec load
and exec.  Additional records could be added as a result of the kexec
load itself.  Let's simplify the title to "ima: make the kexec extra
memory configurable".

Please remove any references to measurements between kexec load and
execute.

On Fri, 2023-12-15 at 17:07 -0800, Tushar Sugandhi wrote:
> IMA currently allocates half a PAGE_SIZE for the extra events that would
> be measured between kexec 'load' and 'execute'.  Depending on the IMA
> policy and the system state, that memory may not be sufficient to hold
> the extra IMA events measured after kexec 'load'.  The memory
> requirements vary from system to system and they should be configurable.

The extra memory allocated for carrying the IMA measurement list across
kexec is hardcoded as a 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 in the
> window from kexec 'load' to kexec 'execute'.

> Update ima_add_kexec_buffer() function to allocate memory based on the 
> Kconfig option value, rather than the currently hardcoded one.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
> ---
>  security/integrity/ima/Kconfig     |  9 +++++++++
>  security/integrity/ima/ima_kexec.c | 13 ++++++++-----
>  2 files changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index 60a511c6b583..8792b7aab768 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -338,3 +338,12 @@ config IMA_DISABLE_HTABLE
>  	default n
>  	help
>  	   This option disables htable to allow measurement of duplicate records.
> +
> +config IMA_KEXEC_EXTRA_MEMORY_KB
> +	int
> +	depends on IMA && IMA_KEXEC
> +	default 64

Since this isn't optional, the default should remain as a half page. 
Since a page is architecture specific, the default will need to be arch
 specific.

thanks,

Mimih

> +	help
> +	  IMA_KEXEC_EXTRA_MEMORY_KB determines the extra memory to be
> +	  allocated (in kb) for IMA measurements added in the window
> +	  from kexec 'load' to kexec 'execute'.
> diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
> index 55bd5362262e..063da9c834a0 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -128,15 +128,18 @@ 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 in the window from
> +	 * kexec 'load' to kexec 'execute'.
>  	 */
> -	binary_runtime_size = ima_get_binary_runtime_size();
> +	binary_runtime_size = ima_get_binary_runtime_size() +
> +			      sizeof(struct ima_kexec_hdr) +
> +			      (CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024);
> +
>  	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);
> +
>  	if ((kexec_segment_size == ULONG_MAX) ||
>  	    ((kexec_segment_size >> PAGE_SHIFT) > totalram_pages() / 2)) {
>  		pr_err("Binary measurement list too large.\n");