linux-kernel - Re: [PATCH v10 7/8] ima: make the kexec extra memory configurable

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Message-ID: <c050bff0-6a0d-402b-884b-fe991cd30cf3@linux.microsoft.com>
Date: Fri, 21 Mar 2025 09:46:47 -0700
From: steven chen <chenste@...ux.microsoft.com>
To: Baoquan He <bhe@...hat.com>
Cc: zohar@...ux.ibm.com, stefanb@...ux.ibm.com,
 roberto.sassu@...weicloud.com, roberto.sassu@...wei.com,
 eric.snowberg@...cle.com, ebiederm@...ssion.com, paul@...l-moore.com,
 code@...icks.com, bauermann@...abnow.com, linux-integrity@...r.kernel.org,
 kexec@...ts.infradead.org, linux-security-module@...r.kernel.org,
 linux-kernel@...r.kernel.org, madvenka@...ux.microsoft.com,
 nramas@...ux.microsoft.com, James.Bottomley@...senpartnership.com,
 vgoyal@...hat.com, dyoung@...hat.com
Subject: Re: [PATCH v10 7/8] ima: make the kexec extra memory configurable

On 3/19/2025 7:52 PM, Baoquan He wrote:
> On 03/17/25 at 06:04pm, steven chen 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@...ux.ibm.com>
>> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>> Signed-off-by: steven chen <chenste@...ux.microsoft.com>
>> Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
>> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
>> ---
>>   security/integrity/ima/Kconfig     | 10 ++++++++++
>>   security/integrity/ima/ima_kexec.c | 16 +++++++++++-----
>>   2 files changed, 21 insertions(+), 5 deletions(-)
>>
>> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
>> index 475c32615006..d73c96c3c1c9 100644
>> --- a/security/integrity/ima/Kconfig
>> +++ b/security/integrity/ima/Kconfig
>> @@ -321,4 +321,14 @@ config IMA_DISABLE_HTABLE
>>   	help
>>   	   This option disables htable to allow measurement of duplicate records.
>>   
>> +config IMA_KEXEC_EXTRA_MEMORY_KB
>> +	int "Extra memory for IMA measurements added during kexec soft reboot"
>> +	depends on IMA_KEXEC
>> +	default 0
> Is there range for this memory, e.g [0, max] and max will be a value
> according to our current perception?

Hi Baoquan,

In the code below there is value check for this

  	if ((kexec_segment_size == ULONG_MAX) ||
  	    ((kexec_segment_size >> PAGE_SHIFT) > totalram_pages() / 2)) {

Hi Mimi,

Could you provide any guidance if we need to set the range?

Thanks,

Steven

>> +	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 of 0, an extra half 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 c390c745f882..0f214e41dd33 100644
>> --- a/security/integrity/ima/ima_kexec.c
>> +++ b/security/integrity/ima/ima_kexec.c
>> @@ -131,6 +131,7 @@ 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_memory;
>>   
>>   	/* use more understandable variable names than defined in kbuf */
>>   	size_t kexec_buffer_size = 0;
>> @@ -138,15 +139,20 @@ 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_memory = PAGE_SIZE / 2;
>> +	else
>> +		extra_memory = CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024;
>> +
>> +	binary_runtime_size = ima_get_binary_runtime_size() + extra_memory;
>> +
>>   	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");
>> -- 
>> 2.25.1
>>
>>