Re: [PATCH v9 2/7] kexec: define functions to map and unmap segments

[steven chen]

On 3/4/2025 2:23 PM, Jarkko Sakkinen wrote:
> On Tue, Mar 04, 2025 at 11:03:46AM -0800, steven chen wrote:
> > The content of memory segments carried over to the new kernel during the
> > kexec systemcall can be changed at kexec 'execute' stage, but the size of
> > the memory segments cannot be changed at kexec 'execute' stage.
> >
> > To copy IMA measurement logs during the kexec operation, IMA needs to
> > allocate memory at the kexec 'load' stage and map the segments to the
> > kimage structure. The mapped address will then be used to copy IMA
> > measurements during the kexec 'execute' stage.
> >
> > Currently, the mechanism to map and unmap segments to the kimage
> > structure is not available to subsystems outside of kexec.
> How does IMA work with kexec without having this? Just interested
> (and confused).
Currently, all IMA-related operations during a soft reboot, such as 
memory allocation and IMA log list copy, are handled in the kexec 'load' 
stage, so the map/unmap mechanism is not required.

The new design separates these two operations into different stages: 
memory allocation remains in the kexec 'load' stage, while the IMA log 
list copy is moved to the kexec 'execute' stage. Therefore, the 
map/unmap mechanism is introduced.

Please refer to "[PATCH v9 0/7] ima: kexec: measure events between kexec 
load and execute" for the reason why to add this.

Steven

> > Implement kimage_map_segment() to enable IMA to map measurement log list to
> > the kimage structure during kexec 'load' stage.  This function takes a kimage
> > pointer, a memory address, and a size, then gathers the
> > source pages within the specified address range, creates an array of page
> > pointers, and maps these to a contiguous virtual address range.  The
> > function returns the start virtual address of this range if successful, or NULL on
> > failure.
> >
> > Implement kimage_unmap_segment() for unmapping segments
> > using vunmap().
> >
> > From: Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>
> > Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> > Cc: Baoquan He <bhe@xxxxxxxxxx>
> > Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> > Cc: Dave Young <dyoung@xxxxxxxxxx>
> > Signed-off-by: steven chen <chenste@xxxxxxxxxxxxxxxxxxx>
> > ---
> >   include/linux/kexec.h |  6 +++++
> >   kernel/kexec_core.c   | 54 +++++++++++++++++++++++++++++++++++++++++++
> >   2 files changed, 60 insertions(+)
> >
> > diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> > index f0e9f8eda7a3..7d6b12f8b8d0 100644
> > --- a/include/linux/kexec.h
> > +++ b/include/linux/kexec.h
> > @@ -467,13 +467,19 @@ extern bool kexec_file_dbg_print;
> >   #define kexec_dprintk(fmt, arg...) \
> >           do { if (kexec_file_dbg_print) pr_info(fmt, ##arg); } while (0)
> >   
> > +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;
> > +struct kimage;
> >   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 c0bdc1686154..63e4d16b6023 100644
> > --- a/kernel/kexec_core.c
> > +++ b/kernel/kexec_core.c
> > @@ -867,6 +867,60 @@ 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("Could not allocate ima pages array.\n");
> > +		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("Could not map ima buffer.\n");
> > +
> > +	return vaddr;
> > +}
> > +
> > +void kimage_unmap_segment(void *segment_buffer)
> > +{
> > +	vunmap(segment_buffer);
> > +}
> > +
> >   struct kexec_load_limit {
> >   	/* Mutex protects the limit count. */
> >   	struct mutex mutex;
> > --
> > 2.25.1
> BR, Jarkko