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kho: make sure page being restored is actually from KHO

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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: Pratyush 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Pratyush Yadav 2025-09-17 14:56:54 +02:00 • committed by Andrew Morton
parent 20571b1870
commit 89a3ecca49
1 changed files with 34 additions and 7 deletions
Download patch file Download diff file Expand all files Collapse all files

41
kernel/kexec_handover.c
View file

@ -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;
}
}