[PATCH RFC 0/5] liveupdate: validate restored LUO metadata

[PATCH RFC 0/5] liveupdate: validate restored LUO metadata

[Cris Jacob Maamor]

LUO restores metadata from KHO/FDT during liveupdate. The restored
metadata contains physical addresses and count fields used to access and
walk preserved session, file-set, and FLB arrays.

This series adds a non-consuming KHO preserved-range check and uses it
before phys_to_virt() on restored metadata addresses. It also rejects
restored counts above LUO_SESSION_MAX, LUO_FILE_MAX, and LUO_FLB_MAX
before traversal.

As far as I can tell, this is root/admin-only; I do not have evidence
that a normal unprivileged user can trigger it directly.

I have not reproduced this in a VM yet, so I may be missing a KHO
invariant or a preferred restore helper pattern. Feedback on the helper
semantics is welcome.

Cris Jacob Maamor (5):
  kexec: handover: add helper to check preserved page ranges
  liveupdate: validate restored LUO FDT before use
  liveupdate: validate restored LUO session metadata
  liveupdate: validate restored LUO file-set metadata
  liveupdate: validate restored LUO FLB metadata

 include/linux/kexec_handover.h     |  6 +++++
 kernel/liveupdate/kexec_handover.c | 35 ++++++++++++++++++++++++++++++
 kernel/liveupdate/luo_core.c       | 10 ++++++++-
 kernel/liveupdate/luo_file.c       | 14 ++++++++++--
 kernel/liveupdate/luo_flb.c        | 23 +++++++++++++++++++-
 kernel/liveupdate/luo_session.c    | 22 +++++++++++++++++--
 6 files changed, 104 insertions(+), 6 deletions(-)

-- 
2.53.0

[PATCH RFC 1/5] kexec: handover: add helper to check preserved page ranges

[Cris Jacob Maamor]

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 include/linux/kexec_handover.h     |  6 +++++
 kernel/liveupdate/kexec_handover.c | 35 ++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index 8968c56d2d73..fb09943ab232 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -19,6 +19,7 @@ struct page;
 #ifdef CONFIG_KEXEC_HANDOVER
 bool kho_is_enabled(void);
 bool is_kho_boot(void);
+bool kho_is_preserved(phys_addr_t phys, unsigned long nr_pages);
 
 int kho_preserve_folio(struct folio *folio);
 void kho_unpreserve_folio(struct folio *folio);
@@ -51,6 +52,11 @@ static inline bool is_kho_boot(void)
 	return false;
 }
 
+static inline bool kho_is_preserved(phys_addr_t phys, unsigned long nr_pages)
+{
+	return false;
+}
+
 static inline int kho_preserve_folio(struct folio *folio)
 {
 	return -EOPNOTSUPP;
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 94762de1fe5f..fe9f11190705 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -10,6 +10,7 @@
 
 #define pr_fmt(fmt) "KHO: " fmt
 
+#include <linux/bits.h>
 #include <linux/cleanup.h>
 #include <linux/cma.h>
 #include <linux/kmemleak.h>
@@ -429,6 +430,40 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)
 	return page;
 }
 
+/**
+ * kho_is_preserved - Verify that a physical page range belongs to KHO.
+ * @phys: physical address of the first page in the range.
+ * @nr_pages: number of pages that the caller expects to access.
+ *
+ * Use this before phys_to_virt() when a physical address comes from restored
+ * metadata. It checks that @phys starts a KHO-preserved allocation large
+ * enough to cover @nr_pages.
+ *
+ * This only checks the KHO marker. It does not restore, free, or take
+ * ownership of the pages.
+ *
+ * Return: true if @phys starts a preserved KHO allocation large enough to cover
+ * @nr_pages, false otherwise.
+ */
+bool kho_is_preserved(phys_addr_t phys, unsigned long nr_pages)
+{
+	struct page *page;
+	union kho_page_info info;
+
+	if (!nr_pages || !IS_ALIGNED(phys, PAGE_SIZE))
+		return false;
+
+	page = pfn_to_online_page(PHYS_PFN(phys));
+	if (!page)
+		return false;
+
+	info.page_private = page->private;
+	if (info.magic != KHO_PAGE_MAGIC || info.order >= BITS_PER_LONG)
+		return false;
+
+	return nr_pages <= BIT(info.order);
+}
+
 /**
  * kho_restore_folio - recreates the folio from the preserved memory.
  * @phys: physical address of the folio.
-- 
2.53.0

Re: [PATCH RFC 1/5] kexec: handover: add helper to check preserved page ranges

[Greg Kroah-Hartman]

On Fri, May 01, 2026 at 05:46:33PM +0800, Cris Jacob Maamor wrote:
> Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>

For obvious reasons, we can't take patches without any changelog text
(nor do you want us to.)

And when a pathc is "RFC", what specific comments are you asking for?
Why don't you feel this is good enough to take now?

thanks,

greg k-h

[PATCH RFC 2/5] liveupdate: validate restored LUO FDT before use

[Cris Jacob Maamor]

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 kernel/liveupdate/luo_core.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c
index 803f51c84275..633a16434164 100644
--- a/kernel/liveupdate/luo_core.c
+++ b/kernel/liveupdate/luo_core.c
@@ -82,6 +82,7 @@ early_param("liveupdate", early_liveupdate_param);
 
 static int __init luo_early_startup(void)
 {
+	size_t fdt_size;
 	phys_addr_t fdt_phys;
 	int err, ln_size;
 	const void *ptr;
@@ -94,7 +95,8 @@ static int __init luo_early_startup(void)
 	}
 
 	/* Retrieve LUO subtree, and verify its format. */
-	err = kho_retrieve_subtree(LUO_FDT_KHO_ENTRY_NAME, &fdt_phys, NULL);
+	err = kho_retrieve_subtree(LUO_FDT_KHO_ENTRY_NAME, &fdt_phys,
+				   &fdt_size);
 	if (err) {
 		if (err != -ENOENT) {
 			pr_err("failed to retrieve FDT '%s' from KHO: %pe\n",
@@ -105,6 +107,12 @@ static int __init luo_early_startup(void)
 		return 0;
 	}
 
+	if (!fdt_size || fdt_size > LUO_FDT_SIZE ||
+	    !kho_is_preserved(fdt_phys, DIV_ROUND_UP(fdt_size, PAGE_SIZE))) {
+		pr_err("Invalid LUO FDT from KHO\n");
+		return -EINVAL;
+	}
+
 	luo_global.fdt_in = phys_to_virt(fdt_phys);
 	err = fdt_node_check_compatible(luo_global.fdt_in, 0,
 					LUO_FDT_COMPATIBLE);
-- 
2.53.0

[PATCH RFC 3/5] liveupdate: validate restored LUO session metadata

[Cris Jacob Maamor]

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 kernel/liveupdate/luo_session.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
index a3327a28fc1f..0244c071936d 100644
--- a/kernel/liveupdate/luo_session.c
+++ b/kernel/liveupdate/luo_session.c
@@ -501,7 +501,18 @@ int __init luo_session_setup_incoming(void *fdt_in)
 	}
 
 	header_ser_pa = get_unaligned((u64 *)ptr);
+	if (!kho_is_preserved(header_ser_pa, LUO_SESSION_PGCNT)) {
+		pr_err("Session header is not KHO preserved: %#llx\n",
+		       (unsigned long long)header_ser_pa);
+		return -EINVAL;
+	}
+
 	header_ser = phys_to_virt(header_ser_pa);
+	if (header_ser->count > LUO_SESSION_MAX) {
+		pr_err("Invalid session count: %llu\n",
+		       (unsigned long long)header_ser->count);
+		return -EINVAL;
+	}
 
 	luo_session_global.incoming.header_ser = header_ser;
 	luo_session_global.incoming.ser = (void *)(header_ser + 1);
@@ -515,6 +526,7 @@ int luo_session_deserialize(void)
 	struct luo_session_header *sh = &luo_session_global.incoming;
 	static bool is_deserialized;
 	static int err;
+	u64 count;
 
 	/* If has been deserialized, always return the same error code */
 	if (is_deserialized)
@@ -524,6 +536,13 @@ int luo_session_deserialize(void)
 	if (!sh->active)
 		return 0;
 
+	count = sh->header_ser->count;
+	if (count > LUO_SESSION_MAX) {
+		pr_err("Invalid session count: %llu\n",
+		       (unsigned long long)count);
+		return -EINVAL;
+	}
+
 	/*
 	 * Note on error handling:
 	 *
@@ -539,7 +558,7 @@ int luo_session_deserialize(void)
 	 * userspace to detect the failure and trigger a reboot, which will
 	 * reliably reset devices and reclaim memory.
 	 */
-	for (int i = 0; i < sh->header_ser->count; i++) {
+	for (u64 i = 0; i < count; i++) {
 		struct luo_session *session;
 
 		session = luo_session_alloc(sh->ser[i].name);
@@ -606,4 +625,3 @@ int luo_session_serialize(void)
 
 	return err;
 }
-
-- 
2.53.0

[PATCH RFC 4/5] liveupdate: validate restored LUO file-set metadata

[Cris Jacob Maamor]

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 kernel/liveupdate/luo_file.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index a0a419085e28..cde43d822f8f 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -783,11 +783,21 @@ int luo_file_deserialize(struct luo_file_set *file_set,
 	struct luo_file_ser *file_ser;
 	u64 i;
 
-	if (!file_set_ser->files) {
-		WARN_ON(file_set_ser->count);
+	if (!file_set_ser->count) {
+		if (file_set_ser->files)
+			return -EINVAL;
 		return 0;
 	}
 
+	if (file_set_ser->count > LUO_FILE_MAX)
+		return -EINVAL;
+
+	if (!file_set_ser->files)
+		return -EINVAL;
+
+	if (!kho_is_preserved(file_set_ser->files, LUO_FILE_PGCNT))
+		return -EINVAL;
+
 	file_set->count = file_set_ser->count;
 	file_set->files = phys_to_virt(file_set_ser->files);
 
-- 
2.53.0

[PATCH RFC 5/5] liveupdate: validate restored LUO FLB metadata

[Cris Jacob Maamor]

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 kernel/liveupdate/luo_flb.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index 00f5494812c4..e80032669cea 100644
--- a/kernel/liveupdate/luo_flb.c
+++ b/kernel/liveupdate/luo_flb.c
@@ -162,6 +162,7 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
 	struct luo_flb_header *fh = &luo_flb_global.incoming;
 	struct liveupdate_flb_op_args args = {0};
 	bool found = false;
+	u64 count;
 	int err;
 
 	guard(mutex)(&private->incoming.lock);
@@ -175,7 +176,14 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
 	if (!fh->active)
 		return -ENODATA;
 
-	for (int i = 0; i < fh->header_ser->count; i++) {
+	count = fh->header_ser->count;
+	if (count > LUO_FLB_MAX) {
+		pr_err("Invalid FLB count: %llu\n",
+		       (unsigned long long)count);
+		return -EINVAL;
+	}
+
+	for (u64 i = 0; i < count; i++) {
 		if (!strcmp(fh->ser[i].name, flb->compatible)) {
 			private->incoming.data = fh->ser[i].data;
 			private->incoming.count = fh->ser[i].count;
@@ -620,7 +628,20 @@ int __init luo_flb_setup_incoming(void *fdt_in)
 	}
 
 	header_ser_pa = get_unaligned((u64 *)ptr);
+	if (!kho_is_preserved(header_ser_pa, LUO_FLB_PGCNT)) {
+		pr_err("FLB header is not KHO preserved: %#llx\n",
+		       (unsigned long long)header_ser_pa);
+		return -EINVAL;
+	}
+
 	header_ser = phys_to_virt(header_ser_pa);
+	if (header_ser->pgcnt != LUO_FLB_PGCNT ||
+	    header_ser->count > LUO_FLB_MAX) {
+		pr_err("Invalid FLB header: pgcnt %llu count %llu\n",
+		       (unsigned long long)header_ser->pgcnt,
+		       (unsigned long long)header_ser->count);
+		return -EINVAL;
+	}
 
 	luo_flb_global.incoming.header_ser = header_ser;
 	luo_flb_global.incoming.ser = (void *)(header_ser + 1);
-- 
2.53.0

[PATCH v2 0/5] liveupdate: validate restored LUO metadata

[Cris Jacob Maamor]

LUO restores metadata from KHO/FDT during liveupdate. The restored
metadata contains physical addresses and count fields used to access and
walk preserved session, file set, and FLB arrays.

This series adds a non-consuming KHO preserved-range check and uses it
before phys_to_virt() on restored metadata addresses. It also rejects
restored counts above LUO_SESSION_MAX, LUO_FILE_MAX, and LUO_FLB_MAX
before traversal.

As far as I can tell, this is root/admin-only; I do not have evidence
that a normal unprivileged user can trigger it directly.

Changes since v1:
- Dropped RFC marking.
- Added changelog text to each patch.
- No code changes.

Cris Jacob Maamor (5):
  kexec: handover: add helper to check preserved page ranges
  liveupdate: validate LUO FDT physical address before mapping
  liveupdate: validate restored LUO session metadata
  liveupdate: validate restored LUO file set metadata
  liveupdate: validate restored LUO FLB metadata

 include/linux/kexec_handover.h     |  6 +++++
 kernel/liveupdate/kexec_handover.c | 35 ++++++++++++++++++++++++++++++
 kernel/liveupdate/luo_core.c       | 10 ++++++++-
 kernel/liveupdate/luo_file.c       | 14 ++++++++++--
 kernel/liveupdate/luo_flb.c        | 23 +++++++++++++++++++-
 kernel/liveupdate/luo_session.c    | 22 +++++++++++++++++--
 6 files changed, 104 insertions(+), 6 deletions(-)

-- 
2.53.0

[PATCH v2 1/5] kexec: handover: add helper to check preserved page ranges

[Cris Jacob Maamor]

Restore code should not use phys_to_virt() on physical addresses from
restored metadata until it verifies that the range was preserved by KHO.

Add kho_is_preserved() so callers can check a preserved page range without
restoring, freeing, or taking ownership of the pages.

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 include/linux/kexec_handover.h     |  6 +++++
 kernel/liveupdate/kexec_handover.c | 35 ++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index 8968c56d2d73..fb09943ab232 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -19,6 +19,7 @@ struct page;
 #ifdef CONFIG_KEXEC_HANDOVER
 bool kho_is_enabled(void);
 bool is_kho_boot(void);
+bool kho_is_preserved(phys_addr_t phys, unsigned long nr_pages);
 
 int kho_preserve_folio(struct folio *folio);
 void kho_unpreserve_folio(struct folio *folio);
@@ -51,6 +52,11 @@ static inline bool is_kho_boot(void)
 	return false;
 }
 
+static inline bool kho_is_preserved(phys_addr_t phys, unsigned long nr_pages)
+{
+	return false;
+}
+
 static inline int kho_preserve_folio(struct folio *folio)
 {
 	return -EOPNOTSUPP;
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 94762de1fe5f..fe9f11190705 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -10,6 +10,7 @@
 
 #define pr_fmt(fmt) "KHO: " fmt
 
+#include <linux/bits.h>
 #include <linux/cleanup.h>
 #include <linux/cma.h>
 #include <linux/kmemleak.h>
@@ -429,6 +430,40 @@ static struct page *kho_restore_page(phys_addr_t phys, bool is_folio)
 	return page;
 }
 
+/**
+ * kho_is_preserved - Verify that a physical page range belongs to KHO.
+ * @phys: physical address of the first page in the range.
+ * @nr_pages: number of pages that the caller expects to access.
+ *
+ * Use this before phys_to_virt() when a physical address comes from restored
+ * metadata. It checks that @phys starts a KHO-preserved allocation large
+ * enough to cover @nr_pages.
+ *
+ * This only checks the KHO marker. It does not restore, free, or take
+ * ownership of the pages.
+ *
+ * Return: true if @phys starts a preserved KHO allocation large enough to cover
+ * @nr_pages, false otherwise.
+ */
+bool kho_is_preserved(phys_addr_t phys, unsigned long nr_pages)
+{
+	struct page *page;
+	union kho_page_info info;
+
+	if (!nr_pages || !IS_ALIGNED(phys, PAGE_SIZE))
+		return false;
+
+	page = pfn_to_online_page(PHYS_PFN(phys));
+	if (!page)
+		return false;
+
+	info.page_private = page->private;
+	if (info.magic != KHO_PAGE_MAGIC || info.order >= BITS_PER_LONG)
+		return false;
+
+	return nr_pages <= BIT(info.order);
+}
+
 /**
  * kho_restore_folio - recreates the folio from the preserved memory.
  * @phys: physical address of the folio.
-- 
2.53.0

[PATCH v2 2/5] liveupdate: validate LUO FDT physical address before mapping

[Cris Jacob Maamor]

LUO gets the restored FDT address from KHO and maps it with phys_to_virt().

Check the FDT size and make sure the address range is KHO-preserved before
mapping it. Reject empty or oversized FDT metadata.

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 kernel/liveupdate/luo_core.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/liveupdate/luo_core.c b/kernel/liveupdate/luo_core.c
index 803f51c84275..633a16434164 100644
--- a/kernel/liveupdate/luo_core.c
+++ b/kernel/liveupdate/luo_core.c
@@ -82,6 +82,7 @@ early_param("liveupdate", early_liveupdate_param);
 
 static int __init luo_early_startup(void)
 {
+	size_t fdt_size;
 	phys_addr_t fdt_phys;
 	int err, ln_size;
 	const void *ptr;
@@ -94,7 +95,8 @@ static int __init luo_early_startup(void)
 	}
 
 	/* Retrieve LUO subtree, and verify its format. */
-	err = kho_retrieve_subtree(LUO_FDT_KHO_ENTRY_NAME, &fdt_phys, NULL);
+	err = kho_retrieve_subtree(LUO_FDT_KHO_ENTRY_NAME, &fdt_phys,
+				   &fdt_size);
 	if (err) {
 		if (err != -ENOENT) {
 			pr_err("failed to retrieve FDT '%s' from KHO: %pe\n",
@@ -105,6 +107,12 @@ static int __init luo_early_startup(void)
 		return 0;
 	}
 
+	if (!fdt_size || fdt_size > LUO_FDT_SIZE ||
+	    !kho_is_preserved(fdt_phys, DIV_ROUND_UP(fdt_size, PAGE_SIZE))) {
+		pr_err("Invalid LUO FDT from KHO\n");
+		return -EINVAL;
+	}
+
 	luo_global.fdt_in = phys_to_virt(fdt_phys);
 	err = fdt_node_check_compatible(luo_global.fdt_in, 0,
 					LUO_FDT_COMPATIBLE);
-- 
2.53.0

[PATCH v2 3/5] liveupdate: validate restored LUO session metadata

[Cris Jacob Maamor]

The restored FDT contains the physical address of the LUO session header,
which LUO maps before reading session metadata. Check that physical range
against KHO-preserved memory before calling phys_to_virt(), and abort the
restore if the physical range is not covered.

The session header has a count that controls how far LUO walks the
serialized session array. Check that count against LUO_SESSION_MAX before
deserialization, and abort the restore if the value is out of range.

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 kernel/liveupdate/luo_session.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/kernel/liveupdate/luo_session.c b/kernel/liveupdate/luo_session.c
index a3327a28fc1f..0244c071936d 100644
--- a/kernel/liveupdate/luo_session.c
+++ b/kernel/liveupdate/luo_session.c
@@ -501,7 +501,18 @@ int __init luo_session_setup_incoming(void *fdt_in)
 	}
 
 	header_ser_pa = get_unaligned((u64 *)ptr);
+	if (!kho_is_preserved(header_ser_pa, LUO_SESSION_PGCNT)) {
+		pr_err("Session header is not KHO preserved: %#llx\n",
+		       (unsigned long long)header_ser_pa);
+		return -EINVAL;
+	}
+
 	header_ser = phys_to_virt(header_ser_pa);
+	if (header_ser->count > LUO_SESSION_MAX) {
+		pr_err("Invalid session count: %llu\n",
+		       (unsigned long long)header_ser->count);
+		return -EINVAL;
+	}
 
 	luo_session_global.incoming.header_ser = header_ser;
 	luo_session_global.incoming.ser = (void *)(header_ser + 1);
@@ -515,6 +526,7 @@ int luo_session_deserialize(void)
 	struct luo_session_header *sh = &luo_session_global.incoming;
 	static bool is_deserialized;
 	static int err;
+	u64 count;
 
 	/* If has been deserialized, always return the same error code */
 	if (is_deserialized)
@@ -524,6 +536,13 @@ int luo_session_deserialize(void)
 	if (!sh->active)
 		return 0;
 
+	count = sh->header_ser->count;
+	if (count > LUO_SESSION_MAX) {
+		pr_err("Invalid session count: %llu\n",
+		       (unsigned long long)count);
+		return -EINVAL;
+	}
+
 	/*
 	 * Note on error handling:
 	 *
@@ -539,7 +558,7 @@ int luo_session_deserialize(void)
 	 * userspace to detect the failure and trigger a reboot, which will
 	 * reliably reset devices and reclaim memory.
 	 */
-	for (int i = 0; i < sh->header_ser->count; i++) {
+	for (u64 i = 0; i < count; i++) {
 		struct luo_session *session;
 
 		session = luo_session_alloc(sh->ser[i].name);
@@ -606,4 +625,3 @@ int luo_session_serialize(void)
 
 	return err;
 }
-
-- 
2.53.0

[PATCH v2 4/5] liveupdate: validate restored LUO file set metadata

[Cris Jacob Maamor]

The restored session metadata provides the LUO file set address and count.
LUO maps that address with phys_to_virt() and uses the restored count to
walk the serialized file array.

Reject invalid empty file set metadata, reject counts above LUO_FILE_MAX,
and check that the physical range is KHO-preserved before mapping it.

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 kernel/liveupdate/luo_file.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/liveupdate/luo_file.c b/kernel/liveupdate/luo_file.c
index a0a419085e28..cde43d822f8f 100644
--- a/kernel/liveupdate/luo_file.c
+++ b/kernel/liveupdate/luo_file.c
@@ -783,11 +783,21 @@ int luo_file_deserialize(struct luo_file_set *file_set,
 	struct luo_file_ser *file_ser;
 	u64 i;
 
-	if (!file_set_ser->files) {
-		WARN_ON(file_set_ser->count);
+	if (!file_set_ser->count) {
+		if (file_set_ser->files)
+			return -EINVAL;
 		return 0;
 	}
 
+	if (file_set_ser->count > LUO_FILE_MAX)
+		return -EINVAL;
+
+	if (!file_set_ser->files)
+		return -EINVAL;
+
+	if (!kho_is_preserved(file_set_ser->files, LUO_FILE_PGCNT))
+		return -EINVAL;
+
 	file_set->count = file_set_ser->count;
 	file_set->files = phys_to_virt(file_set_ser->files);
 
-- 
2.53.0

[PATCH v2 5/5] liveupdate: validate restored LUO FLB metadata

[Cris Jacob Maamor]

The restored FDT contains the physical address of the LUO FLB header, which
LUO maps before using the restored FLB metadata.

Check that the FLB header range is KHO-preserved before calling
phys_to_virt(). Reject invalid page counts and counts above LUO_FLB_MAX
before walking the restored FLB array.

Signed-off-by: Cris Jacob Maamor <crisjacobmaamor@gmail.com>
---
 kernel/liveupdate/luo_flb.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c
index 00f5494812c4..e80032669cea 100644
--- a/kernel/liveupdate/luo_flb.c
+++ b/kernel/liveupdate/luo_flb.c
@@ -162,6 +162,7 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
 	struct luo_flb_header *fh = &luo_flb_global.incoming;
 	struct liveupdate_flb_op_args args = {0};
 	bool found = false;
+	u64 count;
 	int err;
 
 	guard(mutex)(&private->incoming.lock);
@@ -175,7 +176,14 @@ static int luo_flb_retrieve_one(struct liveupdate_flb *flb)
 	if (!fh->active)
 		return -ENODATA;
 
-	for (int i = 0; i < fh->header_ser->count; i++) {
+	count = fh->header_ser->count;
+	if (count > LUO_FLB_MAX) {
+		pr_err("Invalid FLB count: %llu\n",
+		       (unsigned long long)count);
+		return -EINVAL;
+	}
+
+	for (u64 i = 0; i < count; i++) {
 		if (!strcmp(fh->ser[i].name, flb->compatible)) {
 			private->incoming.data = fh->ser[i].data;
 			private->incoming.count = fh->ser[i].count;
@@ -620,7 +628,20 @@ int __init luo_flb_setup_incoming(void *fdt_in)
 	}
 
 	header_ser_pa = get_unaligned((u64 *)ptr);
+	if (!kho_is_preserved(header_ser_pa, LUO_FLB_PGCNT)) {
+		pr_err("FLB header is not KHO preserved: %#llx\n",
+		       (unsigned long long)header_ser_pa);
+		return -EINVAL;
+	}
+
 	header_ser = phys_to_virt(header_ser_pa);
+	if (header_ser->pgcnt != LUO_FLB_PGCNT ||
+	    header_ser->count > LUO_FLB_MAX) {
+		pr_err("Invalid FLB header: pgcnt %llu count %llu\n",
+		       (unsigned long long)header_ser->pgcnt,
+		       (unsigned long long)header_ser->count);
+		return -EINVAL;
+	}
 
 	luo_flb_global.incoming.header_ser = header_ser;
 	luo_flb_global.incoming.ser = (void *)(header_ser + 1);
-- 
2.53.0

Re: [PATCH v2 0/5] liveupdate: validate restored LUO metadata

[Pasha Tatashin]

On 05-02 01:30, Cris Jacob Maamor wrote:
> LUO restores metadata from KHO/FDT during liveupdate. The restored
> metadata contains physical addresses and count fields used to access and
> walk preserved session, file set, and FLB arrays.
> 
> This series adds a non-consuming KHO preserved-range check and uses it
> before phys_to_virt() on restored metadata addresses. It also rejects
> restored counts above LUO_SESSION_MAX, LUO_FILE_MAX, and LUO_FLB_MAX
> before traversal.
> 
> As far as I can tell, this is root/admin-only; I do not have evidence
> that a normal unprivileged user can trigger it directly.
> 
> Changes since v1:
> - Dropped RFC marking.
> - Added changelog text to each patch.
> - No code changes.
> 
> Cris Jacob Maamor (5):
>   kexec: handover: add helper to check preserved page ranges
>   liveupdate: validate LUO FDT physical address before mapping
>   liveupdate: validate restored LUO session metadata
>   liveupdate: validate restored LUO file set metadata
>   liveupdate: validate restored LUO FLB metadata

I have replied separately in the security report to clarify that this is 
not a bug. The behavior follows the ABI specification exactly: we use 
the PA addresses and ranges provided by the KHO FDT tree.

NAK

> 
>  include/linux/kexec_handover.h     |  6 +++++
>  kernel/liveupdate/kexec_handover.c | 35 ++++++++++++++++++++++++++++++
>  kernel/liveupdate/luo_core.c       | 10 ++++++++-
>  kernel/liveupdate/luo_file.c       | 14 ++++++++++--
>  kernel/liveupdate/luo_flb.c        | 23 +++++++++++++++++++-
>  kernel/liveupdate/luo_session.c    | 22 +++++++++++++++++--
>  6 files changed, 104 insertions(+), 6 deletions(-)
> 
> -- 
> 2.53.0
> 

Re: [PATCH v2 0/5] liveupdate: validate restored LUO metadata

[Pratyush Yadav]

Hi Pasha,

On Fri, May 01 2026, Pasha Tatashin wrote:

> On 05-02 01:30, Cris Jacob Maamor wrote:
>> LUO restores metadata from KHO/FDT during liveupdate. The restored
>> metadata contains physical addresses and count fields used to access and
>> walk preserved session, file set, and FLB arrays.
>> 
>> This series adds a non-consuming KHO preserved-range check and uses it
>> before phys_to_virt() on restored metadata addresses. It also rejects
>> restored counts above LUO_SESSION_MAX, LUO_FILE_MAX, and LUO_FLB_MAX
>> before traversal.
>> 
>> As far as I can tell, this is root/admin-only; I do not have evidence
>> that a normal unprivileged user can trigger it directly.
>> 
>> Changes since v1:
>> - Dropped RFC marking.
>> - Added changelog text to each patch.
>> - No code changes.
>> 
>> Cris Jacob Maamor (5):
>>   kexec: handover: add helper to check preserved page ranges
>>   liveupdate: validate LUO FDT physical address before mapping
>>   liveupdate: validate restored LUO session metadata
>>   liveupdate: validate restored LUO file set metadata
>>   liveupdate: validate restored LUO FLB metadata
>
> I have replied separately in the security report to clarify that this is 
> not a bug. The behavior follows the ABI specification exactly: we use 
> the PA addresses and ranges provided by the KHO FDT tree.
>
> NAK

I really do think we should do a restore-only variant for the
kho_alloc_preserve() family of allocators and use it everywhere. It
would prevent problems in the future. Not because the previous kernel is
malicious, but because we might have bugs and the KHO page magic sanity
check acts as a defense in depth.

For example, I am currently looking at a LUO bug where LUO does not
track if a session is outgoing or incoming. So you can do a retrieve()
or finish() on an outgoing session. A lot of nastiness is saved because
of the page magic check. Things like kho_restore_vmalloc() or
kho_restore_folio() fail early and loudly.

If we want to squeeze out more performance later down the line we can
move it behind a debug config, but having this usage pattern of always
restoring before using is going to be a lot more sane than just using
physical addresses willy nilly.

The approach this series takes with kho_is_preserved() is the wrong
design. But a kho_restore() or something similar (maybe we can find a
better name?) is really where we should be going.

-- 
Regards,
Pratyush Yadav