[PATCH 05/10] kexec: implement functions to map and unmap segment to kimage

[Stefan Berger]

On 7/11/23 14:41, Tushar Sugandhi wrote:
> Adding Eric to cc.
> 
> On 7/7/23 05:28, Stefan Berger wrote:
>>
>>
>> On 7/3/23 17:57, Tushar Sugandhi wrote:
>>> Currently, there's no mechanism to map and unmap segments to the kimage
>>> structure.  This functionality is needed when dealing with memory segments
>>> in the context of a kexec operation.
>>>
>>> The patch adds two new functions: kimage_map_segment() and
>>> kimage_unmap_segment().
>>>
>>> Implement kimage_map_segment() which takes a kimage pointer, an address,
>>> and a size.  Ensures that the entire segment is being mapped by comparing
>>> the given address and size to each segment in the kimage's segment array.
>>> Collect the source pages that correspond to the given address range,
>>> allocate an array of pointers to these pages, and map them to a contiguous
>>> range of virtual addresses.  If the mapping operation is successful, the
>>> function returns the start of this range.  Otherwise, it frees the page
>>> pointer array and returns NULL.
>>>
>>> Implement kimage_unmap_segment() that takes a pointer to a segment buffer
>>> and unmaps it using vunmap().
>>>
>>> Finally, move for_each_kimage_entry() macro to kexec.h.
>>>
>>> Note: Use kimage_map_segment() and kimage_unmap_segment() carefully to
>>> avoid memory leaks and ensure that all mapped segments are properly
>>> unmapped when they're no longer needed.
>>>
>>> Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
>>
>>> +
>>> +    i = 0;
>>> +    for_each_kimage_entry(image, ptr, entry) {
>>> +        if (entry & IND_DESTINATION)
>>> +            dest_page_addr = entry & PAGE_MASK;
>>> +        else if (entry & IND_SOURCE) {
>>> +            if (dest_page_addr >= addr && dest_page_addr < eaddr) {
>>> +                src_page_addr = entry & PAGE_MASK;
>>> +                src_pages[i++] = phys_to_page(src_page_addr);
>>
>> Since phys_to_page is not defined on many/most architectures I change it for ppc64 and have successfully used the following:
>>
>> +                               src_pages[i++] = virt_to_page(__va(src_page_addr))
>>
>>
>> After several kexecs the following check still works:
>>
>> # evmctl ima_measurement --ignore-violations /sys/kernel/security/ima/binary_runtime_measurements
>> Matched per TPM bank calculated digest(s).
>>
>>
>>    Stefan
> Thank you so much Stefan for reviewing this series, and catching this
> issue.  Are you suggesting I should use virt_to_page on all architectures
> unconditionally, or use it only when phys_to_page is not available?

I would try to used it on all architectures.

    Stefan

> 
> ~Tushar
> 
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