[PATCH v4 2/2] arm64,ppc64le/kdump: pass dm-crypt keys to kdump kernel

[Coiby Xu]

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, we only need to add
a 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 user space.

[1] https://lore.kernel.org/all/20250502011246.99238-1-coxu@redhat.com/
[2] https://github.com/devicetree-org/dt-schema/pull/181

Cc: Arnaud Lefebvre <arnaud.lefebvre at clever-cloud.com>
Cc: Baoquan he <bhe at redhat.com>
Cc: Dave Young <dyoung at redhat.com>
Cc: Kairui Song <ryncsn at gmail.com>
Cc: Pingfan Liu <kernelfans at gmail.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Krzysztof Kozlowski <krzk at kernel.org>
Cc: Rob Herring <robh at kernel.org>
Cc: Thomas Staudt <tstaudt at de.ibm.com>
Cc: Sourabh Jain <sourabhjain at linux.ibm.com>
Cc: Will Deacon <will at kernel.org>
Signed-off-by: Coiby Xu <coxu at redhat.com>
---
 arch/arm64/kernel/machine_kexec_file.c |  4 ++++
 arch/powerpc/kexec/elf_64.c            |  4 ++++
 drivers/of/fdt.c                       | 21 +++++++++++++++++++++
 drivers/of/kexec.c                     | 19 +++++++++++++++++++
 4 files changed, 48 insertions(+)

diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
index 410060ebd86d..b6798bb2bb82 100644
--- a/arch/arm64/kernel/machine_kexec_file.c
+++ b/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
 
diff --git a/arch/powerpc/kexec/elf_64.c b/arch/powerpc/kexec/elf_64.c
index 5d6d616404cf..ea50a072debf 100644
--- a/arch/powerpc/kexec/elf_64.c
+++ b/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);
diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index 331646d667b9..2967e4aff807 100644
--- a/drivers/of/fdt.c
+++ b/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) {
diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
index 1ee2d31816ae..4bfb1ea5744e 100644
--- a/drivers/of/kexec.c
+++ b/drivers/of/kexec.c
@@ -432,6 +432,25 @@ 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,
-- 
2.53.0