linux-kernel - Re: [PATCH v6 6/7] ima: make the kexec extra memory configurable

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Message-ID: <eeeed6d2-7790-4f2a-8484-23b8d8e9f540@linux.microsoft.com>
Date: Tue, 28 Jan 2025 10:34:02 -0800
From: steven chen <chenste@...ux.microsoft.com>
To: Stefan Berger <stefanb@...ux.ibm.com>, zohar@...ux.ibm.com,
 roberto.sassu@...weicloud.com, petr@...arici.cz, eric.snowberg@...cle.com,
 paul@...l-moore.com, code@...icks.com, nramas@...ux.microsoft.com,
 James.Bottomley@...senPartnership.com, madvenka@...ux.microsoft.com
Cc: linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 6/7] ima: make the kexec extra memory configurable

On 1/28/2025 7:18 AM, Stefan Berger wrote:
>
>
> On 1/24/25 5:55 PM, 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.
>>
>> From: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>> Author: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
>> 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>
>> ---
>>   security/integrity/ima/Kconfig     | 10 ++++++++++
>>   security/integrity/ima/ima_kexec.c | 16 ++++++++++------
>>   2 files changed, 20 insertions(+), 6 deletions(-)
>>
>> diff --git a/security/integrity/ima/Kconfig 
>> b/security/integrity/ima/Kconfig
>> index 475c32615006..7dd2ed8b2cdc 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
>
> int "Extra memory for IMA measurements added during kexec soft reboot"
>
> Without the description I wasn't able to modify the value.
>
>> +    depends on IMA_KEXEC
>> +    default 0
>> +    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, an extra half a 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 d5f004cfeaec..c9c916f69ca7 100644
>> --- a/security/integrity/ima/ima_kexec.c
>> +++ b/security/integrity/ima/ima_kexec.c
>> @@ -128,22 +128,26 @@ 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;
>>       size_t kexec_buffer_size = 0;
>>       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_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");
>
> With the changes to Kconfig:
>
>
> Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
>
Thanks, will update in the next release