Re: [PATCH v2 6/7] ima: make the memory for events between kexec load and exec configurable

[Stefan Berger <stefanb@linux.ibm.com>]

On 10/20/23 16:39, Tushar Sugandhi wrote:

>
>
> On 10/12/23 17:27, Stefan Berger wrote:
>>
>> On 10/5/23 14:26, Tushar Sugandhi wrote:
>>> IMA currently allocates half a PAGE_SIZE for the extra events that 
>>> would
>>> be measured between kexec 'load' and 'execute'.  Depending on the IMA
>>> policy and the system state, that memory may not be sufficient to hold
>>> the extra IMA events measured after kexec 'load'.  The memory
>>> requirements vary from system to system and they should be 
>>> configurable.
>>>
>>> Define a Kconfig option, IMA_KEXEC_EXTRA_PAGES, to configure the number
>>> of extra pages to be allocated for IMA measurements added in the window
>>> from kexec 'load' to kexec 'execute'.
>>>
>>> Update ima_add_kexec_buffer() function to allocate memory based on the
>>> Kconfig option value, rather than the currently hardcoded one.
>>>
>>> Signed-off-by: Tushar Sugandhi<tusharsu@linux.microsoft.com>
>>> ---
>>>   security/integrity/ima/Kconfig     |  9 +++++++++
>>>   security/integrity/ima/ima_kexec.c | 13 ++++++++-----
>>>   2 files changed, 17 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/security/integrity/ima/Kconfig 
>>> b/security/integrity/ima/Kconfig
>>> index 60a511c6b583..1b55cd2bcb36 100644
>>> --- a/security/integrity/ima/Kconfig
>>> +++ b/security/integrity/ima/Kconfig
>>> @@ -338,3 +338,12 @@ config IMA_DISABLE_HTABLE
>>>       default n
>>>       help
>>>          This option disables htable to allow measurement of 
>>> duplicate records.
>>> +
>>> +config IMA_KEXEC_EXTRA_PAGES
>>> +    int
>>> +    depends on IMA && IMA_KEXEC
>>> +    default 16
>>> +    help
>>> +      IMA_KEXEC_EXTRA_PAGES determines the number of extra
>>> +      pages to be allocated for IMA measurements added in the
>>> +      window from kexec 'load' to kexec 'execute'.
>>
>>
>> On ppc64 a page is 64kb. I would ask for additional kb here.
>>
>>
> Not sure I understand.  Do you mean I should make the default value of
> the config IMA_KEXEC_EXTRA_PAGES 64 or something?


No, what I mean is you should ask the user for how many extra kilobytes 
(kb) to allocate - not ask for pages.


    Stefan

>
> In code, I multiply the config value with PAGE_SIZE.  So more memory
> would be allocated on ppc64 for given default config value. Could you
> please clarify what change you are suggesting here?
>
>
> +        binary_runtime_size = ima_get_binary_runtime_size() +
> +                               sizeof(struct ima_kexec_hdr) +
> +                               (CONFIG_IMA_KEXEC_EXTRA_PAGES *
> PAGE_SIZE);
>
> ~Tushar
>
>>> diff --git a/security/integrity/ima/ima_kexec.c 
>>> b/security/integrity/ima/ima_kexec.c
>>> index 13fbbb90319b..6cd5f46a7208 100644
>>> --- a/security/integrity/ima/ima_kexec.c
>>> +++ b/security/integrity/ima/ima_kexec.c
>>> @@ -150,15 +150,18 @@ 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 in the window from
>>> +     * kexec 'load' to kexec 'execute'.
>>>        */
>>> -    binary_runtime_size = ima_get_binary_runtime_size();
>>> +    binary_runtime_size = ima_get_binary_runtime_size() +
>>> +                  sizeof(struct ima_kexec_hdr) +
>>> +                  (CONFIG_IMA_KEXEC_EXTRA_PAGES * PAGE_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");

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