[PATCH v12 3/9] kexec: define functions to map and unmap segments

[Baoquan He]

On 04/20/25 at 05:30am, steven chen wrote:
> On 4/17/2025 9:36 PM, Baoquan He wrote:
> > On 04/15/25 at 07:10pm, steven chen wrote:
> > > From: Steven Chen <chenste at linux.microsoft.com>
> >   ^^^^^^
> > > Implement kimage_map_segment() to enable IMA to map the measurement log
> > > list to the kimage structure during the kexec 'load' stage. This function
> > > gathers the source pages within the specified address range, and maps them
> > > to a contiguous virtual address range.
> > > 
> > > This is a preparation for later usage.
> > > 
> > > Implement kimage_unmap_segment() for unmapping segments using vunmap().
> > > 
> > > From: Tushar Sugandhi <tusharsu at linux.microsoft.com>
> >    ^^^^^^
> > > Signed-off-by: Tushar Sugandhi <tusharsu at linux.microsoft.com>
> >    ^^^^^^^
> > > Cc: Eric Biederman <ebiederm at xmission.com>
> > > Cc: Baoquan He <bhe at redhat.com>
> > > Cc: Vivek Goyal <vgoyal at redhat.com>
> > > Cc: Dave Young <dyoung at redhat.com>
> > > Signed-off-by: steven chen <chenste at linux.microsoft.com>
> >    ^^^^^
> > 
> > The signing on this patch is a little confusing. I can't see who is the
> > real author, who is the co-author, between you and Tushar. You may need
> > to refer to Documentation/process/5.Posting.rst to make that clear.
> 
> Hi Baoquan,
> 
> From my understanding, if there is no change from the original author patch,
> need to add
> From tag and Signed-off-by tag; otherwise, if there are changes,
> Signed-off-by can be used.

If you don't change a patch, you can add your Signed-off-by when
posting. However, the From decides who is the real author. There's no
way to have two From on one patch. My personal understanding.

> 
> Steven
> 
> > > Acked-by: Baoquan He <bhe at redhat.com>
> > > ---
> > >   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..a5e378e1dc7f 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 src_page_addr, dest_page_addr = 0;
> > > +	unsigned long eaddr = addr + size;
> > > +	kimage_entry_t *ptr, entry;
> > > +	struct page **src_pages;
> > > +	unsigned int npages;
> > > +	void *vaddr = NULL;
> > > +	int i;
> > > +
> > > +	/*
> > > +	 * 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;
> > > -- 
> > > 2.43.0
> > > 
>