[PATCH v5 2/8] kexec: define functions to map and unmap segments

[Stefan Berger]

On 2/14/24 10:38, Tushar Sugandhi wrote:
> Currently, the mechanism to map and unmap segments to the kimage
> structure is not available to the subsystems outside of kexec.  This
> functionality is needed when IMA is allocating the memory segments
> during kexec 'load' operation.  Implement functions to map and unmap
> segments to kimage.
> 
> Implement kimage_map_segment() to enable mapping of IMA buffer source
> pages to the kimage structure post kexec 'load'.  This function,
> accepting a kimage pointer, an address, and a size, will gather the
> source pages within the specified address range, create an array of page
> pointers, and map these to a contiguous virtual address range.  The
> function returns the start of this range if successful, or NULL if
> unsuccessful.
> 
> Implement kimage_unmap_segment() for unmapping segments
> using vunmap().  Relocate 'for_each_kimage_entry()' macro from
> kexec_core.c to kexec.h for broader accessibility.
> 
> Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
> ---
>   include/linux/kexec.h | 13 ++++++++++
>   kernel/kexec_core.c   | 59 +++++++++++++++++++++++++++++++++++++++----
>   2 files changed, 67 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 400cb6c02176..3145447eb77a 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -486,6 +486,11 @@ static inline void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages) {
>   static inline void arch_crash_handle_hotplug_event(struct kimage *image) { }
>   #endif
>   
> +#define for_each_kimage_entry(image, ptr, entry) \
> +	for (ptr = &image->head; (entry = *ptr) && !(entry & IND_DONE); \
> +		ptr = (entry & IND_INDIRECTION) ? \
> +			boot_phys_to_virt((entry & PAGE_MASK)) : ptr + 1)
> +
>   int crash_check_update_elfcorehdr(void);
>   
>   #ifndef crash_hotplug_cpu_support
> @@ -507,6 +512,10 @@ extern bool kexec_file_dbg_print;
>   	       kexec_file_dbg_print ? KERN_INFO : KERN_DEBUG,	\
>   	       ##__VA_ARGS__)
>   
> +extern void *kimage_map_segment(struct kimage *image,
> +				unsigned long addr, unsigned long size);
> +extern void kimage_unmap_segment(void *buffer);
> +
>   #else /* !CONFIG_KEXEC_CORE */
>   struct pt_regs;
>   struct task_struct;
> @@ -514,6 +523,10 @@ static inline void __crash_kexec(struct pt_regs *regs) { }
>   static inline void crash_kexec(struct pt_regs *regs) { }
>   static inline int kexec_should_crash(struct task_struct *p) { return 0; }
>   static inline int kexec_crash_loaded(void) { return 0; }
> +static inline void *kimage_map_segment(struct kimage *image,
> +				       unsigned long addr, unsigned long size)
> +{ return NULL; }
> +static inline void kimage_unmap_segment(void *buffer) { }
>   #define kexec_in_progress false
>   #endif /* CONFIG_KEXEC_CORE */
>   
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index d08fc7b5db97..612ad8783bab 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -582,11 +582,6 @@ void kimage_terminate(struct kimage *image)
>   	*image->entry = IND_DONE;
>   }
>   
> -#define for_each_kimage_entry(image, ptr, entry) \
> -	for (ptr = &image->head; (entry = *ptr) && !(entry & IND_DONE); \
> -		ptr = (entry & IND_INDIRECTION) ? \
> -			boot_phys_to_virt((entry & PAGE_MASK)) : ptr + 1)
> -
>   static void kimage_free_entry(kimage_entry_t entry)
>   {
>   	struct page *page;
> @@ -909,6 +904,60 @@ int kimage_load_segment(struct kimage *image,
>   	return result;
>   }
>   
> +void *kimage_map_segment(struct kimage *image,
> +			 unsigned long addr, unsigned long size)
> +{
> +	unsigned long eaddr = addr + size;
> +	unsigned long src_page_addr, dest_page_addr;
> +	unsigned int npages;
> +	struct page **src_pages;
> +	int i;
> +	kimage_entry_t *ptr, entry;
> +	void *vaddr = NULL;
> +
> +	/*
> +	 * Collect the source pages and map them in a contiguous VA range.
> +	 */
> +	npages = PFN_UP(eaddr) - PFN_DOWN(addr);
> +	src_pages = kmalloc_array(npages, sizeof(*src_pages), GFP_KERNEL);
> +	if (!src_pages) {
> +		pr_err("%s: Could not allocate ima pages array.\n", __func__);
> +		return NULL;
> +	}
> +
> +	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++] =
> +					virt_to_page(__va(src_page_addr));
> +				if (i == npages)
> +					break;
> +				dest_page_addr += PAGE_SIZE;
> +			}
> +		}
> +	}
> +
> +	/* Sanity check. */
> +	WARN_ON(i < npages);
> +
> +	vaddr = vmap(src_pages, npages, VM_MAP, PAGE_KERNEL);
> +	kfree(src_pages);
> +
> +	if (!vaddr)
> +		pr_err("%s: Could not map ima buffer.\n", __func__);
> +
> +	return vaddr;
> +}
> +
> +void kimage_unmap_segment(void *segment_buffer)
> +{
> +	vunmap(segment_buffer);
> +}
> +
>   struct kexec_load_limit {
>   	/* Mutex protects the limit count. */
>   	struct mutex mutex;

Reviewed-by: Stefan Berger <stefanb at linux.ibm.com>