+ x86-boot-make-sure-kaslr-does-not-step-over-kho-preserved-memory.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: x86/boot: make sure KASLR does not step over KHO preserved memory
has been added to the -mm mm-unstable branch.  Its filename is
     x86-boot-make-sure-kaslr-does-not-step-over-kho-preserved-memory.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-boot-make-sure-kaslr-does-not-step-over-kho-preserved-memory.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Alexander Graf <graf@amazon.com>
Subject: x86/boot: make sure KASLR does not step over KHO preserved memory
Date: Thu, 1 May 2025 15:54:21 -0700

KHO uses "scratch regions" to bootstrap a kexec'ed kernel.  These regions
are guaranteed to not have any memory that KHO would preserve.

Teach KASLR in decompression code to only consider these scratch regions
when KHO is enabled to make sure preserved memory won't get overwritten.

Link: https://lkml.kernel.org/r/20250501225425.635167-15-changyuanl@google.com
Signed-off-by: Alexander Graf <graf@amazon.com>
Co-developed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Co-developed-by: Changyuan Lyu <changyuanl@google.com>
Signed-off-by: Changyuan Lyu <changyuanl@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/x86/boot/compressed/kaslr.c |   52 ++++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

--- a/arch/x86/boot/compressed/kaslr.c~x86-boot-make-sure-kaslr-does-not-step-over-kho-preserved-memory
+++ a/arch/x86/boot/compressed/kaslr.c
@@ -760,6 +760,55 @@ static void process_e820_entries(unsigne
 	}
 }
 
+/*
+ * If KHO is active, only process its scratch areas to ensure we are not
+ * stepping onto preserved memory.
+ */
+#ifdef CONFIG_KEXEC_HANDOVER
+static bool process_kho_entries(unsigned long minimum, unsigned long image_size)
+{
+	struct kho_scratch *kho_scratch;
+	struct setup_data *ptr;
+	int i, nr_areas = 0;
+
+	ptr = (struct setup_data *)boot_params_ptr->hdr.setup_data;
+	while (ptr) {
+		if (ptr->type == SETUP_KEXEC_KHO) {
+			struct kho_data *kho = (struct kho_data *)ptr->data;
+
+			kho_scratch = (void *)kho->scratch_addr;
+			nr_areas = kho->scratch_size / sizeof(*kho_scratch);
+
+			break;
+		}
+
+		ptr = (struct setup_data *)ptr->next;
+	}
+
+	if (!nr_areas)
+		return false;
+
+	for (i = 0; i < nr_areas; i++) {
+		struct kho_scratch *area = &kho_scratch[i];
+		struct mem_vector region = {
+			.start = area->addr,
+			.size = area->size,
+		};
+
+		if (process_mem_region(&region, minimum, image_size))
+			break;
+	}
+
+	return true;
+}
+#else
+static inline bool process_kho_entries(unsigned long minimum,
+				       unsigned long image_size)
+{
+	return false;
+}
+#endif
+
 static unsigned long find_random_phys_addr(unsigned long minimum,
 					   unsigned long image_size)
 {
@@ -775,7 +824,8 @@ static unsigned long find_random_phys_ad
 		return 0;
 	}
 
-	if (!process_efi_entries(minimum, image_size))
+	if (!process_kho_entries(minimum, image_size) &&
+	    !process_efi_entries(minimum, image_size))
 		process_e820_entries(minimum, image_size);
 
 	phys_addr = slots_fetch_random();
_

Patches currently in -mm which might be from graf@amazon.com are

memblock-add-support-for-scratch-memory.patch
kexec-add-kexec-handover-kho-generation-helpers.patch
kexec-add-kho-parsing-support.patch
kexec-add-kho-support-to-kexec-file-loads.patch
kexec-add-config-option-for-kho.patch
arm64-add-kho-support.patch
x86-kexec-add-support-for-passing-kexec-handover-kho-data.patch
x86-e820-temporarily-enable-kho-scratch-for-memory-below-1m.patch
x86-boot-make-sure-kaslr-does-not-step-over-kho-preserved-memory.patch
x86-kconfig-enable-kexec-handover-for-64-bits.patch
memblock-add-kho-support-for-reserve_mem.patch
documentation-add-documentation-for-kho.patch