[PATCH v9 1/6] kho: add size parameter to kho_add_subtree()

Breno Leitao
2026-03-16T11:56:14Z

kho_add_subtree() assumes the fdt argument is always an FDT and calls
fdt_totalsize() on it in the debugfs code path. This assumption will
break if a caller passes arbitrary data instead of an FDT.

When CONFIG_KEXEC_HANDOVER_DEBUGFS is enabled, kho_debugfs_fdt_add()
calls __kho_debugfs_fdt_add(), which executes:

f->wrapper.size = fdt_totalsize(fdt);

Fix this by adding an explicit size parameter to kho_add_subtree() so
callers specify the blob size. This allows subtrees to contain
arbitrary data formats, not just FDTs. Update all callers:

- memblock.c: use fdt_totalsize(fdt)
- luo_core.c: use fdt_totalsize(fdt_out)
- test_kho.c: use fdt_totalsize()
- kexec_handover.c (root fdt): use fdt_totalsize(kho_out.fdt)

Also update __kho_debugfs_fdt_add() to receive the size explicitly
instead of computing it internally via fdt_totalsize(). In
kho_in_debugfs_init(), pass fdt_totalsize() for the root FDT and
sub-blobs since all current users are FDTs. A subsequent patch will
persist the size in the KHO FDT so the incoming side can handle
non-FDT blobs correctly.

Suggested-by: Pratyush Yadav <pratyush@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
include/linux/kexec_handover.h | 4 ++--
kernel/liveupdate/kexec_handover.c | 8 +++++---
kernel/liveupdate/kexec_handover_debugfs.c | 15 +++++++++------
kernel/liveupdate/kexec_handover_internal.h | 5 +++--
kernel/liveupdate/luo_core.c | 3 ++-
lib/test_kho.c | 3 ++-
mm/memblock.c | 2 +-
7 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index ac4129d1d7416..abb1d324f42d0 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -32,7 +32,7 @@ void kho_restore_free(void *mem);
struct folio *kho_restore_folio(phys_addr_t phys);
struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages);
void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);
-int kho_add_subtree(const char *name, void *fdt);
+int kho_add_subtree(const char *name, void *fdt, size_t size);
void kho_remove_subtree(void *fdt);
int kho_retrieve_subtree(const char *name, phys_addr_t *phys);

@@ -97,7 +97,7 @@ static inline void *kho_restore_vmalloc(const struct kho_vmalloc *preservation)
return NULL;
}

-static inline int kho_add_subtree(const char *name, void *fdt)
+static inline int kho_add_subtree(const char *name, void *fdt, size_t size)
{
return -EOPNOTSUPP;
}
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index b64f36a452965..55bdc5d2d1929 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -752,6 +752,7 @@ static void __init kho_reserve_scratch(void)
* kho_add_subtree - record the physical address of a sub FDT in KHO root tree.
* @name: name of the sub tree.
* @fdt: the sub tree blob.
+ * @size: size of the blob in bytes.
*
* Creates a new child node named @name in KHO root FDT and records
* the physical address of @fdt. The pages of @fdt must also be preserved
@@ -763,7 +764,7 @@ static void __init kho_reserve_scratch(void)
*
* Return: 0 on success, error code on failure
*/
-int kho_add_subtree(const char *name, void *fdt)
+int kho_add_subtree(const char *name, void *fdt, size_t size)
{
phys_addr_t phys = virt_to_phys(fdt);
void *root_fdt = kho_out.fdt;
@@ -788,7 +789,7 @@ int kho_add_subtree(const char *name, void *fdt)
if (err < 0)
goto out_pack;

- WARN_ON_ONCE(kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, false));
+ WARN_ON_ONCE(kho_debugfs_fdt_add(&kho_out.dbg, name, fdt, size, false));

out_pack:
fdt_pack(root_fdt);
@@ -1452,7 +1453,8 @@ static __init int kho_init(void)
}

WARN_ON_ONCE(kho_debugfs_fdt_add(&kho_out.dbg, "fdt",
- kho_out.fdt, true));
+ kho_out.fdt,
+ fdt_totalsize(kho_out.fdt), true));

return 0;

diff --git a/kernel/liveupdate/kexec_handover_debugfs.c b/kernel/liveupdate/kexec_handover_debugfs.c
index acf3682226824..ca0153736af13 100644
--- a/kernel/liveupdate/kexec_handover_debugfs.c
+++ b/kernel/liveupdate/kexec_handover_debugfs.c
@@ -25,7 +25,7 @@ struct fdt_debugfs {
};

static int __kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir,
- const char *name, const void *fdt)
+ const char *name, const void *fdt, size_t size)
{
struct fdt_debugfs *f;
struct dentry *file;
@@ -35,7 +35,7 @@ static int __kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir,
return -ENOMEM;

f->wrapper.data = (void *)fdt;
- f->wrapper.size = fdt_totalsize(fdt);
+ f->wrapper.size = size;

file = debugfs_create_blob(name, 0400, dir, &f->wrapper);
if (IS_ERR(file)) {
@@ -50,7 +50,7 @@ static int __kho_debugfs_fdt_add(struct list_head *list, struct dentry *dir,
}

int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name,
- const void *fdt, bool root)
+ const void *fdt, size_t size, bool root)
{
struct dentry *dir;

@@ -59,7 +59,7 @@ int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name,
else
dir = dbg->sub_fdt_dir;

- return __kho_debugfs_fdt_add(&dbg->fdt_list, dir, name, fdt);
+ return __kho_debugfs_fdt_add(&dbg->fdt_list, dir, name, fdt, size);
}

void kho_debugfs_fdt_remove(struct kho_debugfs *dbg, void *fdt)
@@ -113,7 +113,8 @@ __init void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt)
goto err_rmdir;
}

- err = __kho_debugfs_fdt_add(&dbg->fdt_list, dir, "fdt", fdt);
+ err = __kho_debugfs_fdt_add(&dbg->fdt_list, dir, "fdt", fdt,
+ fdt_totalsize(fdt));
if (err)
goto err_rmdir;

@@ -121,6 +122,7 @@ __init void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt)
int len = 0;
const char *name = fdt_get_name(fdt, child, NULL);
const u64 *fdt_phys;
+ void *sub_fdt;

fdt_phys = fdt_getprop(fdt, child, KHO_FDT_SUB_TREE_PROP_NAME, &len);
if (!fdt_phys)
@@ -130,8 +132,9 @@ __init void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt)
name, len);
continue;
}
+ sub_fdt = phys_to_virt(*fdt_phys);
err = __kho_debugfs_fdt_add(&dbg->fdt_list, sub_fdt_dir, name,
- phys_to_virt(*fdt_phys));
+ sub_fdt, fdt_totalsize(sub_fdt));
if (err) {
pr_warn("failed to add fdt %s to debugfs: %pe\n", name,
ERR_PTR(err));
diff --git a/kernel/liveupdate/kexec_handover_internal.h b/kernel/liveupdate/kexec_handover_internal.h
index 9a832a35254cf..2a28cb8db9b0a 100644
--- a/kernel/liveupdate/kexec_handover_internal.h
+++ b/kernel/liveupdate/kexec_handover_internal.h
@@ -27,7 +27,7 @@ int kho_debugfs_init(void);
void kho_in_debugfs_init(struct kho_debugfs *dbg, const void *fdt);
int kho_out_debugfs_init(struct kho_debugfs *dbg);
int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name,
- const void *fdt, bool root);
+ const void *fdt, size_t size, bool root);
void kho_debugfs_fdt_remove(struct kho_debugfs *dbg, void *fdt);
#else
static inline int kho_debugfs_init(void) { return 0; }
@@ -35,7 +35,8 @@ static inline void kho_in_debugfs_init(struct kho_debugfs *dbg,
const void *fdt) { }
static inline int kho_out_debugfs_init(struct kho_debugfs *dbg) { return 0; }
static inline int kho_debugfs_fdt_add(struct kho_debugfs *dbg, const char *name,
- const void *fdt, bool root) { return 0; }
+ const void *fdt, size_t size,
+ bool root) { return 0; }
static inline void kho_debugfs_fdt_remove(struct kho_debugfs *dbg,
void *fdt) { }
#endif /* CONFIG_KEXEC_HANDOVER_DEBUGFS */
diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c
index 84ac728d63baa..04d06a0906c0e 100644
--- a/kernel/liveupdate/luo_core.c
+++ b/kernel/liveupdate/luo_core.c
@@ -172,7 +172,8 @@ static int __init luo_fdt_setup(void)
if (err)
goto exit_free;

- err = kho_add_subtree(LUO_FDT_KHO_ENTRY_NAME, fdt_out);
+ err = kho_add_subtree(LUO_FDT_KHO_ENTRY_NAME, fdt_out,
+ fdt_totalsize(fdt_out));
if (err)
goto exit_free;
luo_global.fdt_out = fdt_out;
diff --git a/lib/test_kho.c b/lib/test_kho.c
index 7ef9e40618696..2631824373152 100644
--- a/lib/test_kho.c
+++ b/lib/test_kho.c
@@ -143,7 +143,8 @@ static int kho_test_preserve(struct kho_test_state *state)
if (err)
goto err_unpreserve_data;

- err = kho_add_subtree(KHO_TEST_FDT, folio_address(state->fdt));
+ err = kho_add_subtree(KHO_TEST_FDT, folio_address(state->fdt),
+ fdt_totalsize(folio_address(state->fdt)));
if (err)
goto err_unpreserve_data;

diff --git a/mm/memblock.c b/mm/memblock.c
index ae6a5af46bd78..29e12ea2a854c 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2488,7 +2488,7 @@ static int __init prepare_kho_fdt(void)
if (err)
goto err_unpreserve_fdt;

- err = kho_add_subtree(MEMBLOCK_KHO_FDT, fdt);
+ err = kho_add_subtree(MEMBLOCK_KHO_FDT, fdt, fdt_totalsize(fdt));
if (err)
goto err_unpreserve_fdt;

--
2.52.0