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]/
---
kernel/kexec_core.c | 12 +++---------
1 file changed, 3 insertions(+), 9 deletions(-)
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 31203f0bacaf..3b279d9e0d01 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -761,9 +761,7 @@ static int kimage_load_cma_segment(struct kimage *image,
int idx)
while (mbytes) {
size_t uchunk, mchunk;
- ptr += maddr & ~PAGE_MASK;
- mchunk = min_t(size_t, mbytes,
- PAGE_SIZE - (maddr & ~PAGE_MASK));
+ mchunk = min_t(size_t, mbytes, PAGE_SIZE);
uchunk = min(ubytes, mchunk);
if (uchunk) {
@@ -840,9 +838,7 @@ static int kimage_load_normal_segment(struct kimage *image,
int idx)
ptr = kmap_local_page(page);
/* Start with a clear page */
clear_page(ptr);
- ptr += maddr & ~PAGE_MASK;
- mchunk = min_t(size_t, mbytes,
- PAGE_SIZE - (maddr & ~PAGE_MASK));
+ mchunk = min_t(size_t, mbytes, PAGE_SIZE);
uchunk = min(ubytes, mchunk);
if (uchunk) {
@@ -905,9 +901,7 @@ static int kimage_load_crash_segment(struct kimage *image,
int idx)
}
arch_kexec_post_alloc_pages(page_address(page), 1, 0);
ptr = kmap_local_page(page);
- ptr += maddr & ~PAGE_MASK;
- mchunk = min_t(size_t, mbytes,
- PAGE_SIZE - (maddr & ~PAGE_MASK));
+ mchunk = min_t(size_t, mbytes, PAGE_SIZE);
uchunk = min(ubytes, mchunk);
if (mchunk > uchunk) {
/* Zero the trailing part of the page */
--
2.43.0
