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

From: Stefan Berger <stefanb@linux.ibm.com>
To: Tushar Sugandhi <tusharsu@linux.microsoft.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
Subject: Re: [PATCH 05/10] kexec: implement functions to map and unmap segment to kimage
Date: Fri, 7 Jul 2023 08:28:17 -0400	[thread overview]
Message-ID: <ab4c5f9a-5b70-5d45-80d9-2ec48ea49913@linux.ibm.com> (raw)
In-Reply-To: <20230703215709.1195644-6-tusharsu@linux.microsoft.com>

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

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