Re: [PATCH v4 6/7] ima: make the kexec extra memory configurable

[Tushar Sugandhi <tusharsu@linux.microsoft.com>]

On 1/24/24 06:07, Mimi Zohar wrote:
> 
>> --- a/security/integrity/ima/ima_kexec.c
>> +++ b/security/integrity/ima/ima_kexec.c
>> @@ -121,6 +121,7 @@ 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;
>> @@ -128,15 +129,19 @@ 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.
>>   	 */
> 
> The memory is still being allocated at kexec "load",  so the extra memory is for
> additional measurement records "since" kexec load.
> 
> Mimi
> 
This wording was an attempt to address the comment in v3[1].
So I tried to make the comment generic.  But maybe I made it too generic.
I will update.

[1] Re: [PATCH v3 6/7] ima: configure memory to log events between kexec 
load and execute
https://lore.kernel.org/all/fbe6aa7577875b23a9913a39f858f06f1d2aa903.camel@linux.ibm.com/

"Additional records could be added as a result of the kexec
load itself.
...
Please remove any references to measurements between kexec load and
execute."

~Tushar

>> -	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;
>> +
>>   	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");
>