linux-kernel - Re: [PATCH v11 8/9] ima: make the kexec extra memory configurable

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Message-ID: <8b5e5495-4b11-4acc-8df1-fb94b2a34f0f@linux.microsoft.com>
Date: Thu, 10 Apr 2025 09:59:41 -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 v11 8/9] ima: make the kexec extra memory configurable

On 4/10/2025 2:54 AM, Baoquan He wrote:
> On 04/02/25 at 05:47am, 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
> Usually a new Kconfig item which accepts a range should define the range
> boundary, otherwise it's not clear to people how large or how small it
> can be set. For example, can I set it as value of 1<<40? We should at
> least estimate a possible upper limit for it for other people's
> reference. My personal opinion.

Hi Baoquan,

How about I set range 2-40? Default set as 2, same as the fixed setting.

Thanks,

Steven

> The rest looks good to me.
>
>
>> +	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
> ...snip...