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kexec_core: remove superfluous page offset handling in segment loading

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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);

[jbouron@amazon.com: v3]
  Link: https://lkml.kernel.org/r/20251024155009.39502-1-jbouron@amazon.com
Link: https://lkml.kernel.org/r/20250929160220.47616-1-jbouron@amazon.com
Signed-off-by: Justinien Bouron <jbouron@amazon.com>
Reviewed-by: Gunnar Kudrjavets <gunnarku@amazon.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: Marcos Paulo de Souza <mpdesouza@suse.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Justinien Bouron
2025-09-29 09:02:20 -07:00
committed by Andrew Morton
parent 8a7d58845f
commit 6a2e57ad22
1 changed files with 3 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
kernel/kexec_core.c
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@@ -742,7 +742,6 @@ static int kimage_load_cma_segment(struct kimage *image, int idx)
struct kexec_segment *segment = &image->segment[idx];
struct page *cma = image->segment_cma[idx];
char *ptr = page_address(cma);
unsigned long maddr;
size_t ubytes, mbytes;
int result = 0;
unsigned char __user *buf = NULL;
@@ -754,15 +753,12 @@ static int kimage_load_cma_segment(struct kimage *image, int idx)
buf = segment->buf;
ubytes = segment->bufsz;
mbytes = segment->memsz;
maddr = segment->mem;
/* Then copy from source buffer to the CMA one */
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) {
@@ -784,7 +780,6 @@ static int kimage_load_cma_segment(struct kimage *image, int idx)
}
ptr += mchunk;
maddr += mchunk;
mbytes -= mchunk;
cond_resched();
@@ -839,9 +834,7 @@ 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) {
@@ -904,9 +897,7 @@ 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 */