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

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Message-ID: <692121f5-fc17-45b5-b4c0-c4393bb05bc4@linux.microsoft.com>
Date: Thu, 10 Apr 2025 11:49:34 -0700
From: steven chen <chenste@...ux.microsoft.com>
To: Mimi Zohar <zohar@...ux.ibm.com>, Baoquan He <bhe@...hat.com>,
 Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
Cc: 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, 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 11:04 AM, Mimi Zohar wrote:
> On Thu, 2025-04-10 at 09:59 -0700, steven chen wrote:
>> 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.
> 0, the current default, sets the "extra" memory to the existing "extra half a
> page of memory for the additional measurements".  For backwards compatibility,
> please do not change this.
>
> The requirement for a larger "extra" measurement is coming from Microsoft. If
> this isn't any longer a requirement, we could drop this patch.  Lakshmi, do you
> have any thoughts on this?
>
> thanks,
>
> Mimi

How about the range set as 0-40 and the default as 0?

We (Microsoft) are ok with 0 as the default.

Thanks

>>> 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...
>>
>>