kho: verify deserialization status and fix FDT alignment access

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.

Link: https://lkml.kernel.org/r/20251114190002.3311679-6-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baoquan He <bhe@redhat.com>
Cc: Coiby Xu <coxu@redhat.com>
Cc: Dave Vasilevsky <dave@vasilevsky.ca>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Kees Cook <kees@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 704e914182141f2e044a72a9396dd52968411b61..bed611bae1dfb0d9f6eec2742e90b07b2c386c38 100644 (file)
--- 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();
        }