[PATCH v2 05/13] kho: Verify deserialization status and fix FDT alignment access

Pasha Tatashin
2025-11-14T19:00:13Z

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 get_unaligned() 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 <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
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 704e91418214..bed611bae1df 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -18,6 +18,7 @@
#include <linux/list.h>
#include <linux/memblock.h>
#include <linux/page-isolation.h>
+#include <linux/unaligned.h>
#include <linux/vmalloc.h>

#include <asm/early_ioremap.h>
@@ -451,20 +452,27 @@ 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;
}

- chunk = *mem ? phys_to_virt(*mem) : NULL;
+ mem = get_unaligned((const u64 *)mem_ptr);
+ chunk = mem ? phys_to_virt(mem) : NULL;
+
+ /* No preserved physical pages were passed, no deserialization */
+ if (!chunk)
+ return false;
+
while (chunk) {
unsigned int i;

@@ -473,6 +481,8 @@ static void __init kho_mem_deserialize(const void *fdt)
&chunk->bitmaps[i]);
chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
}
+
+ return true;
}

/*
@@ -1458,16 +1468,12 @@ 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;
} else {
kho_reserve_scratch();
}
--
2.52.0.rc1.455.g30608eb744-goog