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

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

Le 11/02/2026 à 09:24, Coiby Xu a écrit :
> 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

What do you want to say exactly with 'only' ?

> 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://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F20250502011246.99238-1-coxu%40redhat.com%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C0aa5f3b34d694b23b0cc08de6946f66c%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639063950684962054%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=8uCc%2Bg6YNojymf8UpZhmJY19vpWXJCC9KIf3qMyQ3dI%3D&reserved=0
> [2] https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fdevicetree-org%2Fdt-schema%2Fpull%2F181&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C0aa5f3b34d694b23b0cc08de6946f66c%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639063950684987003%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=1s5NPHgF1LsXdrDXBhawduFXOqnHPlkbohQHHvolLw4%3D&reserved=0
> 
> 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: Andrew Morton <akpm@linux-foundation.org>
> Cc: Krzysztof Kozlowski <krzk@kernel.org>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Thomas Staudt <tstaudt@de.ibm.com>
> Cc: Sourabh Jain <sourabhjain@linux.ibm.com>
> Cc: Will Deacon <will@kernel.org>
> Signed-off-by: Coiby Xu <coxu@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/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);

Shouldn't this property be deleted regardless of whether kernel is built 
with CONFIG_CRASH_DM_CRYPT or without ?

> +}
> +
>   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) {