arm64,ppc64le/kdump: pass dm-crypt keys to kdump kernel

CONFIG_CRASH_DM_CRYPT has been introduced to support LUKS-encrypted
device dump target by addressing two challenges [1],
 - Kdump kernel may not be able to decrypt the LUKS partition. For some
   machines, a system administrator may not have a chance to enter the
   password to decrypt the device in kdump initramfs after the 1st kernel
   crashes

 - LUKS2 by default use the memory-hard Argon2 key derivation function
   which is quite memory-consuming compared to the limited memory reserved
   for kdump.

To also enable this feature for ARM64 and PowerPC, the missing piece is to
let the kdump kernel know where to find the dm-crypt keys which are
randomly stored in memory reserved for kdump.  Introduce a new device tree
property dmcryptkeys [2] as similar to elfcorehdr to pass the memory
address of the stored info of dm-crypt keys to the kdump kernel.  Since
this property is only needed by the kdump kernel, it won't be exposed to
userspace.

Link: https://lkml.kernel.org/r/20260225060347.718905-4-coxu@redhat.com
Link: https://lore.kernel.org/all/20250502011246.99238-1-coxu@redhat.com/ [1]
Link: https://github.com/devicetree-org/dt-schema/pull/181 [2]
Signed-off-by: Coiby Xu <coxu@redhat.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Cc: Arnaud Lefebvre <arnaud.lefebvre@clever-cloud.com>
Cc: Baoquan he <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Pingfan Liu <kernelfans@gmail.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Thomas Staudt <tstaudt@de.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/arm64/kernel/machine_kexec_file.c

@@ -134,6 +134,10 @@ int load_other_segments(struct kimage *image,
 
 		kexec_dprintk("Loaded elf core header at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
 			      image->elf_load_addr, kbuf.bufsz, kbuf.memsz);
+
+		ret = crash_load_dm_crypt_keys(image);
+		if (ret)
+			goto out_err;
 	}
 #endif
 

arch/powerpc/kexec/elf_64.c

@@ -79,6 +79,10 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
 			goto out;
 		}
 
+		ret = crash_load_dm_crypt_keys(image);
+		if (ret)
+			goto out;
+
 		/* Setup cmdline for kdump kernel case */
 		modified_cmdline = setup_kdump_cmdline(image, cmdline,
 						       cmdline_len);

drivers/of/fdt.c

@@ -866,6 +866,26 @@ static void __init early_init_dt_check_for_elfcorehdr(unsigned long node)
 		 elfcorehdr_addr, elfcorehdr_size);
 }
 
+static void __init early_init_dt_check_for_dmcryptkeys(unsigned long node)
+{
+	const char *prop_name = "linux,dmcryptkeys";
+	const __be32 *prop;
+
+	if (!IS_ENABLED(CONFIG_CRASH_DM_CRYPT))
+		return;
+
+	pr_debug("Looking for dmcryptkeys property... ");
+
+	prop = of_get_flat_dt_prop(node, prop_name, NULL);
+	if (!prop)
+		return;
+
+	dm_crypt_keys_addr = dt_mem_next_cell(dt_root_addr_cells, &prop);
+
+	/* Property only accessible to crash dump kernel */
+	fdt_delprop(initial_boot_params, node, prop_name);
+}
+
 static unsigned long chosen_node_offset = -FDT_ERR_NOTFOUND;
 
 /*
@@ -1097,6 +1117,7 @@ int __init early_init_dt_scan_chosen(char *cmdline)
 
 	early_init_dt_check_for_initrd(node);
 	early_init_dt_check_for_elfcorehdr(node);
+	early_init_dt_check_for_dmcryptkeys(node);
 
 	rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l);
 	if (rng_seed && l > 0) {

drivers/of/kexec.c

@@ -423,6 +423,25 @@ void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
 		if (ret)
 			goto out;
 
+		if (image->dm_crypt_keys_addr != 0) {
+			ret = fdt_appendprop_addrrange(fdt, 0, chosen_node,
+						       "linux,dmcryptkeys",
+						       image->dm_crypt_keys_addr,
+						       image->dm_crypt_keys_sz);
+
+			if (ret)
+				goto out;
+
+			/*
+			 * Avoid dmcryptkeys from being stomped on in kdump kernel by
+			 * setting up memory reserve map.
+			 */
+			ret = fdt_add_mem_rsv(fdt, image->dm_crypt_keys_addr,
+					      image->dm_crypt_keys_sz);
+			if (ret)
+				goto out;
+		}
+
 #ifdef CONFIG_CRASH_DUMP
 		/* add linux,usable-memory-range */
 		ret = fdt_appendprop_addrrange(fdt, 0, chosen_node,