Commit 89a3ecca authored by Pratyush Yadav's avatar Pratyush Yadav Committed by Andrew Morton
Browse files

kho: make sure page being restored is actually from KHO 

When restoring a page, no sanity checks are done to make sure the page
actually came from a kexec handover.  The caller is trusted to pass in the
right address.  If the caller has a bug and passes in a wrong address, an
in-use page might be "restored" and returned, causing all sorts of memory
corruption.

Harden the page restore logic by stashing in a magic number in
page->private along with the order.  If the magic number does not match,
the page won't be touched.  page->private is an unsigned long.  The union
kho_page_info splits it into two parts, with one holding the order and the
other holding the magic number.

Link: https://lkml.kernel.org/r/20250917125725.665-2-pratyush@kernel.org


Signed-off-by: default avatarPratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 20571b18

kernel/kexec_handover.c

+34 −7
Original line number Diff line number Diff line
@@ -32,6 +32,22 @@ 
#define PROP_PRESERVED_MEMORY_MAP "preserved-memory-map"

#define PROP_SUB_FDT "fdt"



#define KHO_PAGE_MAGIC 0x4b484f50U /* ASCII for 'KHOP' */



/*

 * KHO uses page->private, which is an unsigned long, to store page metadata.

 * Use it to store both the magic and the order.

 */

union kho_page_info {

	unsigned long page_private;

	struct {

		unsigned int order;

		unsigned int magic;

	};

};



static_assert(sizeof(union kho_page_info) == sizeof(((struct page *)0)->private));



static bool kho_enable __ro_after_init;



bool kho_is_enabled(void)
@@ -186,16 +202,24 @@ static int __kho_preserve_order(struct kho_mem_track *track, unsigned long pfn, 
static struct page *kho_restore_page(phys_addr_t phys)

{

	struct page *page = pfn_to_online_page(PHYS_PFN(phys));

	unsigned int nr_pages, order;

	union kho_page_info info;

	unsigned int nr_pages;



	if (!page)

		return NULL;



	order = page->private;

	if (order > MAX_PAGE_ORDER)

	info.page_private = page->private;

	/*

	 * deserialize_bitmap() only sets the magic on the head page. This magic

	 * check also implicitly makes sure phys is order-aligned since for

	 * non-order-aligned phys addresses, magic will never be set.

	 */

	if (WARN_ON_ONCE(info.magic != KHO_PAGE_MAGIC || info.order > MAX_PAGE_ORDER))

		return NULL;

	nr_pages = (1 << order);

	nr_pages = (1 << info.order);



	/* Clear private to make sure later restores on this page error out. */

	page->private = 0;

	/* Head page gets refcount of 1. */

	set_page_count(page, 1);
@@ -203,8 +227,8 @@ static struct page *kho_restore_page(phys_addr_t phys) 
	for (unsigned int i = 1; i < nr_pages; i++)

		set_page_count(page + i, 0);



	if (order > 0)

		prep_compound_page(page, order);

	if (info.order > 0)

		prep_compound_page(page, info.order);



	adjust_managed_page_count(page, nr_pages);

	return page;
@@ -341,10 +365,13 @@ static void __init deserialize_bitmap(unsigned int order, 
		phys_addr_t phys =

			elm->phys_start + (bit << (order + PAGE_SHIFT));

		struct page *page = phys_to_page(phys);

		union kho_page_info info;



		memblock_reserve(phys, sz);

		memblock_reserved_mark_noinit(phys, sz);

		page->private = order;

		info.magic = KHO_PAGE_MAGIC;

		info.order = order;

		page->private = info.page_private;

	}

}