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

Jarkko Sakkinen
2025-03-04T22:23:07Z

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).

>
> 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@linux.microsoft.com>
> Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
> Cc: Eric Biederman <ebiederm@xmission.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: Dave Young <dyoung@redhat.com>
> Signed-off-by: steven chen <chenste@linux.microsoft.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..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