+ 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: Fri, 9 May 2025 00:46:31 -0700

During kexec handover (KHO) memory contains data that should be preserved
and this data would be consumed by kexec'ed kernel.

To make sure that the preserved memory is not overwritten, KHO uses
"scratch regions" to bootstrap kexec'ed kernel.  These regions are
guaranteed to not have any memory that KHO would preserve and are used as
the only memory the kernel sees during the early boot.

The scratch regions are passed in the setup_data by the first kernel with
other KHO parameters.  If the setup_data contains the KHO parameters,
limit randomization to scratch areas only to make sure preserved memory
won't get overwritten.

Since all the pointers in setup_data are represented by u64, they require
double casting (first to unsigned long and then to the actual pointer
type) to compile on 32-bits.  This looks goofy out of context, but it is
unfortunately the way that this is handled across the tree.  There are at
least a dozen instances of casting like this.

Link: https://lkml.kernel.org/r/20250509074635.3187114-14-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>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Anthony Yznaga <anthony.yznaga@oracle.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ashish Kalra <ashish.kalra@amd.com>
Cc: Ben Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Gowans <jgowans@amazon.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Pratyush Yadav <ptyadav@amazon.de>
Cc: Rob Herring <robh@kernel.org>
Cc: Saravana Kannan <saravanak@google.com>
Cc: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Thomas Lendacky <thomas.lendacky@amd.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/x86/boot/compressed/kaslr.c |   50 ++++++++++++++++++++++++++++-
 1 file changed, 49 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 +760,49 @@ static void process_e820_entries(unsigne
 	}
 }
 
+/*
+ * If KHO is active, only process its scratch areas to ensure we are not
+ * stepping onto preserved memory.
+ */
+static bool process_kho_entries(unsigned long minimum, unsigned long image_size)
+{
+	struct kho_scratch *kho_scratch;
+	struct setup_data *ptr;
+	struct kho_data *kho;
+	int i, nr_areas = 0;
+
+	if (!IS_ENABLED(CONFIG_KEXEC_HANDOVER))
+		return false;
+
+	ptr = (struct setup_data *)(unsigned long)boot_params_ptr->hdr.setup_data;
+	while (ptr) {
+		if (ptr->type == SETUP_KEXEC_KHO) {
+			kho = (struct kho_data *)(unsigned long)ptr->data;
+			kho_scratch = (void *)(unsigned long)kho->scratch_addr;
+			nr_areas = kho->scratch_size / sizeof(*kho_scratch);
+			break;
+		}
+
+		ptr = (struct setup_data *)(unsigned long)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;
+}
+
 static unsigned long find_random_phys_addr(unsigned long minimum,
 					   unsigned long image_size)
 {
@@ -775,7 +818,12 @@ static unsigned long find_random_phys_ad
 		return 0;
 	}
 
-	if (!process_efi_entries(minimum, image_size))
+	/*
+	 * During kexec handover only process KHO scratch areas that are known
+	 * not to contain any data that must be preserved.
+	 */
+	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