Hi Marco,
On Sat, Feb 14, 2026 at 01:57:51AM +0100, Marco Elver wrote:
> The function deserialize_bitmap() calculates the reservation size using:
>
> int sz = 1 << (order + PAGE_SHIFT);
>
> If a corrupted KHO image provides an order >= 20 (on systems with 4KB
> pages), the shift amount becomes >= 32, which overflows the 32-bit
> integer. This results in a zero-size memory reservation.
>
> Furthermore, the physical address calculation:
>
> phys_addr_t phys = elm->phys_start + (bit << (order + PAGE_SHIFT));
>
> can also overflow and wrap around if the order is large. This allows a
> corrupt KHO image to cause out-of-bounds updates to page->private of
> arbitrary physical pages during early boot.
>
> Fix this by adding a bounds check for the order field.
>
> Fixes: fc33e4b44b27 ("kexec: enable KHO support for memory preservation")
> Signed-off-by: Marco Elver <[email protected]>
> ---
> kernel/liveupdate/kexec_handover.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/liveupdate/kexec_handover.c
> b/kernel/liveupdate/kexec_handover.c
> index b851b09a8e99..ec353e4b68a6 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -463,6 +463,11 @@ static void __init deserialize_bitmap(unsigned int order,
> struct kho_mem_phys_bits *bitmap = KHOSER_LOAD_PTR(elm->bitmap);
> unsigned long bit;
>
> + if (order > MAX_PAGE_ORDER) {
Preserved order can be larger than MAX_PAGE_ORDER.
Let's make 'sz' unsigned long and add checks that calculations won't
overflow.
> + pr_warn("invalid order %u for preserved bitmap\n", order);
> + return;
> + }
> +
> for_each_set_bit(bit, bitmap->preserve, PRESERVE_BITS) {
> int sz = 1 << (order + PAGE_SHIFT);
> phys_addr_t phys =
> --
> 2.53.0.335.g19a08e0c02-goog
--
Sincerely yours,
Mike.
