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: Tue, 11 Jul 2023 11:41:23 -0700	[thread overview]
Message-ID: <7f38366e-744e-78c8-cf05-acfeb59afd2e@linux.microsoft.com> (raw)
In-Reply-To: <ab4c5f9a-5b70-5d45-80d9-2ec48ea49913@linux.ibm.com>

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?

~Tushar