On 10/24/25 at 08:50am, Justinien Bouron wrote:
> During kexec_segment loading, when copying the content of the segment
> (i.e. kexec_segment::kbuf or kexec_segment::buf) to its associated
> pages, kimage_load_{cma,normal,crash}_segment handle the case where the
> physical address of the segment is not page aligned, e.g. in
> kimage_load_normal_segment:
> ```
> page = kimage_alloc_page(image, GFP_HIGHUSER, maddr);
> // ...
> ptr = kmap_local_page(page);
> // ...
> ptr += maddr & ~PAGE_MASK;
> mchunk = min_t(size_t, mbytes,
> PAGE_SIZE - (maddr & ~PAGE_MASK));
> // ^^^^ Non page-aligned segments handled here ^^^
> // ...
> if (image->file_mode)
> memcpy(ptr, kbuf, uchunk);
> else
> result = copy_from_user(ptr, buf, uchunk);
> ```
> (similar logic is present in kimage_load_{cma,crash}_segment).
>
> This is actually not needed because, prior to their loading, all
> kexec_segments first go through a vetting step in
> `sanity_check_segment_list`, which rejects any segment that is not
> page-aligned:
> ```
> for (i = 0; i < nr_segments; i++) {
> unsigned long mstart, mend;
> mstart = image->segment[i].mem;
> mend = mstart + image->segment[i].memsz;
> // ...
> if ((mstart & ~PAGE_MASK) || (mend & ~PAGE_MASK))
> return -EADDRNOTAVAIL;
> // ...
> }
> ```
> In case `sanity_check_segment_list` finds a non-page aligned the whole
> kexec load is aborted and no segment is loaded.
>
> This means that `kimage_load_{cma,normal,crash}_segment` never actually
> have to handle non page-aligned segments and `(maddr & ~PAGE_MASK) == 0`
> is always true no matter if the segment is coming from a file (i.e.
> `kexec_file_load` syscall), from a user-space buffer (i.e. `kexec_load`
> syscall) or created by the kernel through `kexec_add_buffer`. In the
> latter case, `kexec_add_buffer` actually enforces the page alignment:
> ```
> /* Ensure minimum alignment needed for segments. */
> kbuf->memsz = ALIGN(kbuf->memsz, PAGE_SIZE);
> kbuf->buf_align = max(kbuf->buf_align, PAGE_SIZE);
> ```
>
> Signed-off-by: Justinien Bouron <[email protected]>
> Reviewed-by: Gunnar Kudrjavets <[email protected]>
> ---
> Changes since v1:
> - Reworked commit message as requested by Baoquan He
> <[email protected]>
> - Removed accidental whitespace change
> - v1 Link:
> https://lore.kernel.org/lkml/[email protected]/
>
> Changes since v2:
> - Removed unused variable in kimage_load_cma_segment() which was
> causing a warning and failing build with `make W=1`. Thanks
> Andy Shevchenko for finding this issue
> - v2 Link:
> https://lore.kernel.org/lkml/[email protected]/
> ---
> kernel/kexec_core.c | 15 +++------------
> 1 file changed, 3 insertions(+), 12 deletions(-)
LGTM, thanks.
Acked-by: Baoquan He <[email protected]>
