kho: preserve FDT folio only once during initialization

Currently, the FDT folio is preserved inside __kho_finalize().  If the
user performs multiple finalize/abort cycles, kho_preserve_folio() is
called repeatedly for the same FDT folio.

Since the FDT folio is allocated once during kho_init(), it should be
marked for preservation at the same time.  Move the preservation call to
kho_init() to align the preservation state with the object's lifecycle and
simplify the finalize path.

Also, pre-zero the FDT tree so we do not expose random bits to the user
and to the next kernel by using the new kho_alloc_preserve() api.

Link: https://lkml.kernel.org/r/20251114190002.3311679-5-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 5c5c9c46fe923e9dadbf428c144a294fdeff54cd..704e914182141f2e044a72a9396dd52968411b61 100644 (file)
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -1251,10 +1251,6 @@ static int __kho_finalize(void)
        if (err)
                goto abort;
 
-       err = kho_preserve_folio(virt_to_folio(kho_out.fdt));
-       if (err)
-               goto abort;
-
        err = kho_mem_serialize(&kho_out);
        if (err)
                goto abort;
@@ -1384,19 +1380,17 @@ EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
 
 static __init int kho_init(void)
 {
-       int err = 0;
        const void *fdt = kho_get_fdt();
-       struct page *fdt_page;
+       int err = 0;
 
        if (!kho_enable)
                return 0;
 
-       fdt_page = alloc_page(GFP_KERNEL);
-       if (!fdt_page) {
-               err = -ENOMEM;
+       kho_out.fdt = kho_alloc_preserve(PAGE_SIZE);
+       if (IS_ERR(kho_out.fdt)) {
+               err = PTR_ERR(kho_out.fdt);
                goto err_free_scratch;
        }
-       kho_out.fdt = page_to_virt(fdt_page);
 
        err = kho_debugfs_init();
        if (err)
@@ -1424,9 +1418,9 @@ static __init int kho_init(void)
        return 0;
 
 err_free_fdt:
-       put_page(fdt_page);
-       kho_out.fdt = NULL;
+       kho_unpreserve_free(kho_out.fdt);
 err_free_scratch:
+       kho_out.fdt = NULL;
        for (int i = 0; i < kho_scratch_cnt; i++) {
                void *start = __va(kho_scratch[i].addr);
                void *end = start + kho_scratch[i].size;