On Fri, Nov 14 2025, Pasha Tatashin wrote:
> During boot, kho_restore_folio() relies on the memory map having been
> successfully deserialized. If deserialization fails or no map is present,
> attempting to restore the FDT folio is unsafe.
>
> Update kho_mem_deserialize() to return a boolean indicating success. Use
> this return value in kho_memory_init() to disable KHO if deserialization
> fails. Also, the incoming FDT folio is never used, there is no reason to
> restore it.
>
> Additionally, use memcpy() to retrieve the memory map pointer from the FDT.
> FDT properties are not guaranteed to be naturally aligned, and accessing
> a 64-bit value via a pointer that is only 32-bit aligned can cause faults.
>
> Signed-off-by: Pasha Tatashin <[email protected]>
> ---
> kernel/liveupdate/kexec_handover.c | 32 ++++++++++++++++++------------
> 1 file changed, 19 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/liveupdate/kexec_handover.c
> b/kernel/liveupdate/kexec_handover.c
> index a4b33ca79246..83aca3b4af15 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -450,20 +450,28 @@ static void __init deserialize_bitmap(unsigned int
> order,
> }
> }
>
> -static void __init kho_mem_deserialize(const void *fdt)
> +/* Return true if memory was deserizlied */
> +static bool __init kho_mem_deserialize(const void *fdt)
> {
> struct khoser_mem_chunk *chunk;
> - const phys_addr_t *mem;
> + const void *mem_ptr;
> + u64 mem;
> int len;
>
> - mem = fdt_getprop(fdt, 0, PROP_PRESERVED_MEMORY_MAP, &len);
> -
> - if (!mem || len != sizeof(*mem)) {
> + mem_ptr = fdt_getprop(fdt, 0, PROP_PRESERVED_MEMORY_MAP, &len);
> + if (!mem_ptr || len != sizeof(u64)) {
> pr_err("failed to get preserved memory bitmaps\n");
> - return;
> + return false;
> }
> + /* FDT guarantees 32-bit alignment, have to use memcpy */
> + memcpy(&mem, mem_ptr, len);
Perhaps get_unaligned(mem) would have been simpler?
> +
> + chunk = mem ? phys_to_virt(mem) : NULL;
> +
> + /* No preserved physical pages were passed, no deserialization */
> + if (!chunk)
> + return false;
Should we disallow all kho_restore_{folio,pages}() calls too if this
fails? Ideally those should never happen since kho_retrieve_subtree()
will fail, so maybe as a debug aid?
>
> - chunk = *mem ? phys_to_virt(*mem) : NULL;
> while (chunk) {
> unsigned int i;
>
> @@ -472,6 +480,8 @@ static void __init kho_mem_deserialize(const void *fdt)
> &chunk->bitmaps[i]);
> chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
> }
> +
> + return true;
> }
>
> /*
> @@ -1377,16 +1387,12 @@ static void __init kho_release_scratch(void)
>
> void __init kho_memory_init(void)
> {
> - struct folio *folio;
> -
> if (kho_in.scratch_phys) {
> kho_scratch = phys_to_virt(kho_in.scratch_phys);
> kho_release_scratch();
>
> - kho_mem_deserialize(kho_get_fdt());
> - folio = kho_restore_folio(kho_in.fdt_phys);
> - if (!folio)
> - pr_warn("failed to restore folio for KHO fdt\n");
> + if (!kho_mem_deserialize(kho_get_fdt()))
> + kho_in.fdt_phys = 0;
The folio restore does serve a purpose: it accounts for that folio in
the system's total memory. See the call to adjust_managed_page_count()
in kho_restore_page(). In practice, I don't think it makes much of a
difference, but I don't see why not.
> } else {
> kho_reserve_scratch();
> }
--
Regards,
Pratyush Yadav
