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

From: Tushar Sugandhi <tusharsu@linux.microsoft.com>
To: Stefan Berger <stefanb@linux.ibm.com>,
	zohar@linux.ibm.com, noodles@fb.com, bauermann@kolabnow.com,
	kexec@lists.infradead.org, linux-integrity@vger.kernel.org
Cc: code@tyhicks.com, nramas@linux.microsoft.com,
	paul@paul-moore.com, Eric Biederman <ebiederm@xmission.com>
Subject: Re: [PATCH 05/10] kexec: implement functions to map and unmap segment to kimage
Date: Wed, 12 Jul 2023 12:51:29 -0700	[thread overview]
Message-ID: <7ece0f6d-3c11-eeea-e540-c6dff707b06c@linux.microsoft.com> (raw)
In-Reply-To: <4ccfe980-3c71-fa06-59e4-56c85d798224@linux.ibm.com>


On 7/11/23 12:19, Stefan Berger wrote:
>
>
> 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@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
>
Ok.  Thanks.
>>
>> ~Tushar
>>
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