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

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Message-ID: <20251114190002.3311679-6-pasha.tatashin@soleen.com>
Date: Fri, 14 Nov 2025 13:59:54 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: akpm@...ux-foundation.org,
	bhe@...hat.com,
	pasha.tatashin@...een.com,
	rppt@...nel.org,
	jasonmiu@...gle.com,
	arnd@...db.de,
	coxu@...hat.com,
	dave@...ilevsky.ca,
	ebiggers@...gle.com,
	graf@...zon.com,
	kees@...nel.org,
	linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org,
	linux-mm@...ck.org
Subject: [PATCH v2 05/13] 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.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.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