[PATCH] kho: validate preserved memory map during population

[PATCH] kho: validate preserved memory map during population

[Pasha Tatashin]

If the previous kernel enabled KHO but did not call kho_finalize()
(e.g., CONFIG_LIVEUPDATE=n or userspace skipped the finalization step),
the 'preserved-memory-map' property in the FDT remains empty/zero.

Previously, kho_populate() would succeed regardless of the memory map's
state, reserving the incoming scratch regions in memblock. However,
kho_memory_init() would later fail to deserialize the empty map. By that
time, the scratch regions were already registered, leading to partial
initialization and subsequent list corruption (double-free) during
kho_init().

Move the validation of the preserved memory map earlier into
kho_populate(). If the memory map is empty/NULL:
1. Abort kho_populate() immediately with -ENOENT.
2. Do not register or reserve the incoming scratch memory, allowing the new
   kernel to reclaim those pages as standard free memory.
3. Leave the global 'kho_in' state uninitialized.

Consequently, kho_memory_init() sees no active KHO context
(kho_in.mem_chunks is NULL) and falls back to kho_reserve_scratch(),
allocating fresh scratch memory as if it were a standard cold boot.

Fixes: de51999e687c ("kho: allow memory preservation state updates after finalization")
Reported-by: Ricardo <ricardo@example.com>
Closes: https://lore.kernel.org/all/20251218215613.GA17304@ranerica-svr.sc.intel.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 kernel/liveupdate/kexec_handover.c | 36 +++++++++++++++++-------------
 1 file changed, 21 insertions(+), 15 deletions(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 9dc51fab604f..96c708f753d4 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -460,10 +460,9 @@ static void __init deserialize_bitmap(unsigned int order,
 	}
 }
 
-/* Return true if memory was deserizlied */
-static bool __init kho_mem_deserialize(const void *fdt)
+/* Returns head of preserved physical memory chunks pointer from FDT */
+static struct khoser_mem_chunk * __init kho_get_mem_chunks(const void *fdt)
 {
-	struct khoser_mem_chunk *chunk;
 	const void *mem_ptr;
 	u64 mem;
 	int len;
@@ -471,16 +470,16 @@ static bool __init kho_mem_deserialize(const void *fdt)
 	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 false;
+		return 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;
+	return mem ? phys_to_virt(mem) : NULL;
+}
 
+static void __init kho_mem_deserialize(struct khoser_mem_chunk *chunk)
+{
 	while (chunk) {
 		unsigned int i;
 
@@ -489,8 +488,6 @@ static bool __init kho_mem_deserialize(const void *fdt)
 					   &chunk->bitmaps[i]);
 		chunk = KHOSER_LOAD_PTR(chunk->hdr.next);
 	}
-
-	return true;
 }
 
 /*
@@ -1253,6 +1250,7 @@ bool kho_finalized(void)
 struct kho_in {
 	phys_addr_t fdt_phys;
 	phys_addr_t scratch_phys;
+	struct khoser_mem_chunk *mem_chunks;
 	struct kho_debugfs dbg;
 };
 
@@ -1434,12 +1432,10 @@ static void __init kho_release_scratch(void)
 
 void __init kho_memory_init(void)
 {
-	if (kho_in.scratch_phys) {
+	if (kho_in.mem_chunks) {
 		kho_scratch = phys_to_virt(kho_in.scratch_phys);
 		kho_release_scratch();
-
-		if (!kho_mem_deserialize(kho_get_fdt()))
-			kho_in.fdt_phys = 0;
+		kho_mem_deserialize(kho_in.mem_chunks);
 	} else {
 		kho_reserve_scratch();
 	}
@@ -1448,8 +1444,9 @@ void __init kho_memory_init(void)
 void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
 			 phys_addr_t scratch_phys, u64 scratch_len)
 {
-	void *fdt = NULL;
+	struct khoser_mem_chunk *mem_chunks;
 	struct kho_scratch *scratch = NULL;
+	void *fdt = NULL;
 	int err = 0;
 	unsigned int scratch_cnt = scratch_len / sizeof(*kho_scratch);
 
@@ -1475,6 +1472,14 @@ void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
 		goto out;
 	}
 
+	mem_chunks = kho_get_mem_chunks(fdt);
+	if (!mem_chunks) {
+		pr_warn("setup: handover FDT (0x%llx) present but no preserved memory found\n",
+			fdt_phys);
+		err = -ENOENT;
+		goto out;
+	}
+
 	scratch = early_memremap(scratch_phys, scratch_len);
 	if (!scratch) {
 		pr_warn("setup: failed to memremap scratch (phys=0x%llx, len=%lld)\n",
@@ -1515,6 +1520,7 @@ void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
 
 	kho_in.fdt_phys = fdt_phys;
 	kho_in.scratch_phys = scratch_phys;
+	kho_in.mem_chunks = mem_chunks;
 	kho_scratch_cnt = scratch_cnt;
 	pr_info("found kexec handover data.\n");
 
-- 
2.52.0.322.g1dd061c0dc-goog

Re: [PATCH] kho: validate preserved memory map during population

[Pasha Tatashin]

On Thu, Dec 18, 2025 at 7:23 PM Pasha Tatashin
<pasha.tatashin@soleen.com> wrote:
>
> If the previous kernel enabled KHO but did not call kho_finalize()
> (e.g., CONFIG_LIVEUPDATE=n or userspace skipped the finalization step),
> the 'preserved-memory-map' property in the FDT remains empty/zero.
>
> Previously, kho_populate() would succeed regardless of the memory map's
> state, reserving the incoming scratch regions in memblock. However,
> kho_memory_init() would later fail to deserialize the empty map. By that
> time, the scratch regions were already registered, leading to partial
> initialization and subsequent list corruption (double-free) during
> kho_init().
>
> Move the validation of the preserved memory map earlier into
> kho_populate(). If the memory map is empty/NULL:
> 1. Abort kho_populate() immediately with -ENOENT.
> 2. Do not register or reserve the incoming scratch memory, allowing the new
>    kernel to reclaim those pages as standard free memory.
> 3. Leave the global 'kho_in' state uninitialized.
>
> Consequently, kho_memory_init() sees no active KHO context
> (kho_in.mem_chunks is NULL) and falls back to kho_reserve_scratch(),
> allocating fresh scratch memory as if it were a standard cold boot.
>
> Fixes: de51999e687c ("kho: allow memory preservation state updates after finalization")
> Reported-by: Ricardo <ricardo@example.com>
> Closes: https://lore.kernel.org/all/20251218215613.GA17304@ranerica-svr.sc.intel.com
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
>  kernel/liveupdate/kexec_handover.c | 36 +++++++++++++++++-------------
>  1 file changed, 21 insertions(+), 15 deletions(-)
>
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 9dc51fab604f..96c708f753d4 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -460,10 +460,9 @@ static void __init deserialize_bitmap(unsigned int order,
>         }
>  }
>
> -/* Return true if memory was deserizlied */
> -static bool __init kho_mem_deserialize(const void *fdt)
> +/* Returns head of preserved physical memory chunks pointer from FDT */
> +static struct khoser_mem_chunk * __init kho_get_mem_chunks(const void *fdt)
>  {
> -       struct khoser_mem_chunk *chunk;
>         const void *mem_ptr;
>         u64 mem;
>         int len;
> @@ -471,16 +470,16 @@ static bool __init kho_mem_deserialize(const void *fdt)
>         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 false;
> +               return 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;
> +       return mem ? phys_to_virt(mem) : NULL;

I need to update this patch, phys_to_virt() should not be called from
kho_populate() before KASLR is initialized. This causes a problem with
my live update test. I will send a new version soon.

Pasha

Re: [PATCH] kho: validate preserved memory map during population

[Ricardo Neri]

On Thu, Dec 18, 2025 at 07:49:11PM -0500, Pasha Tatashin wrote:
> On Thu, Dec 18, 2025 at 7:23 PM Pasha Tatashin
> <pasha.tatashin@soleen.com> wrote:
> >
> > If the previous kernel enabled KHO but did not call kho_finalize()
> > (e.g., CONFIG_LIVEUPDATE=n or userspace skipped the finalization step),
> > the 'preserved-memory-map' property in the FDT remains empty/zero.
> >
> > Previously, kho_populate() would succeed regardless of the memory map's
> > state, reserving the incoming scratch regions in memblock. However,
> > kho_memory_init() would later fail to deserialize the empty map. By that
> > time, the scratch regions were already registered, leading to partial
> > initialization and subsequent list corruption (double-free) during
> > kho_init().
> >
> > Move the validation of the preserved memory map earlier into
> > kho_populate(). If the memory map is empty/NULL:
> > 1. Abort kho_populate() immediately with -ENOENT.
> > 2. Do not register or reserve the incoming scratch memory, allowing the new
> >    kernel to reclaim those pages as standard free memory.
> > 3. Leave the global 'kho_in' state uninitialized.
> >
> > Consequently, kho_memory_init() sees no active KHO context
> > (kho_in.mem_chunks is NULL) and falls back to kho_reserve_scratch(),
> > allocating fresh scratch memory as if it were a standard cold boot.
> >
> > Fixes: de51999e687c ("kho: allow memory preservation state updates after finalization")
> > Reported-by: Ricardo <ricardo@example.com>
> > Closes: https://lore.kernel.org/all/20251218215613.GA17304@ranerica-svr.sc.intel.com
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> > ---
> >  kernel/liveupdate/kexec_handover.c | 36 +++++++++++++++++-------------
> >  1 file changed, 21 insertions(+), 15 deletions(-)
> >
> > diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> > index 9dc51fab604f..96c708f753d4 100644
> > --- a/kernel/liveupdate/kexec_handover.c
> > +++ b/kernel/liveupdate/kexec_handover.c
> > @@ -460,10 +460,9 @@ static void __init deserialize_bitmap(unsigned int order,
> >         }
> >  }
> >
> > -/* Return true if memory was deserizlied */
> > -static bool __init kho_mem_deserialize(const void *fdt)
> > +/* Returns head of preserved physical memory chunks pointer from FDT */
> > +static struct khoser_mem_chunk * __init kho_get_mem_chunks(const void *fdt)
> >  {
> > -       struct khoser_mem_chunk *chunk;
> >         const void *mem_ptr;
> >         u64 mem;
> >         int len;
> > @@ -471,16 +470,16 @@ static bool __init kho_mem_deserialize(const void *fdt)
> >         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 false;
> > +               return 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;
> > +       return mem ? phys_to_virt(mem) : NULL;
> 
> I need to update this patch, phys_to_virt() should not be called from
> kho_populate() before KASLR is initialized. This causes a problem with
> my live update test. I will send a new version soon.

Thanks for the patch Pasha! FWIW, I no longer see the issue I reported.
I will test your v2 when posted.

BR,
Ricardo
> 
> Pasha