Re: [PATCH] powerpc/kdump: pass dm-crypt keys to kdump kernel

[Sourabh Jain <sourabhjain@linux.ibm.com>]

On 26/12/25 19:36, Coiby Xu wrote:
> Based on the CONFIG_CRASH_DM_CRYPT feature, this patch adds
> LUKS-encrypted device dump target support to PowerPC 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.
>
> 1st kernel will build up the kernel command parameter dmcryptkeys as
> similar to elfcorehdr to pass the memory address of the stored info of
> dm-crypt keys to the kdump kernel.
>
> [1] https://lore.kernel.org/all/20250502011246.99238-1-coxu@redhat.com/
>
> Cc: Thomas Staudt <tstaudt@de.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: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Coiby Xu <coxu@redhat.com>
> ---
>   arch/powerpc/include/asm/kexec.h |  3 ++-
>   arch/powerpc/kexec/elf_64.c      | 26 +++++++++++++++++++++++++-
>   arch/powerpc/kexec/file_load.c   | 19 +++++++++++--------
>   3 files changed, 38 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kexec.h b/arch/powerpc/include/asm/kexec.h
> index bd4a6c42a5f3..f3d098d543b4 100644
> --- a/arch/powerpc/include/asm/kexec.h
> +++ b/arch/powerpc/include/asm/kexec.h
> @@ -80,7 +80,8 @@ struct kimage_arch {
>   };
>   
>   char *setup_kdump_cmdline(struct kimage *image, char *cmdline,
> -			  unsigned long cmdline_len);
> +			  unsigned long cmdline_len,
> +			  char *name, unsigned long addr);
>   int setup_purgatory(struct kimage *image, const void *slave_code,
>   		    const void *fdt, unsigned long kernel_load_addr,
>   		    unsigned long fdt_load_addr);
> diff --git a/arch/powerpc/kexec/elf_64.c b/arch/powerpc/kexec/elf_64.c
> index 5d6d616404cf..57cb3361d91b 100644
> --- a/arch/powerpc/kexec/elf_64.c
> +++ b/arch/powerpc/kexec/elf_64.c
> @@ -81,13 +81,37 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
>   
>   		/* Setup cmdline for kdump kernel case */
>   		modified_cmdline = setup_kdump_cmdline(image, cmdline,
> -						       cmdline_len);
> +						       cmdline_len,
> +						       "elfcorehdr",
> +						       image->elf_load_addr);
>   		if (!modified_cmdline) {
>   			pr_err("Setting up cmdline for kdump kernel failed\n");
>   			ret = -EINVAL;
>   			goto out;
>   		}
>   		cmdline = modified_cmdline;
> +		cmdline_len = strlen(cmdline) + 1;
> +
> +		ret = crash_load_dm_crypt_keys(image);
> +		if (ret == -ENOENT) {
> +			kexec_dprintk("No dm crypt key to load\n");
> +		} else if (ret) {
> +			pr_err("Failed to load dm crypt keys\n");
> +			return ERR_PTR(ret);
> +		}
> +
> +		if (image->dm_crypt_keys_addr != 0) {
> +			modified_cmdline = setup_kdump_cmdline(image, cmdline,
> +							       cmdline_len,
> +							       "dmcryptkeys",
> +							       image->dm_crypt_keys_addr);
> +			if (!modified_cmdline) {
> +				pr_err("Setting up cmdline for kdump kernel failed\n");
> +				ret = -EINVAL;
> +				goto out;
> +			}
> +			cmdline = modified_cmdline;
> +		}
>   	}
>   
>   	if (initrd != NULL) {
> diff --git a/arch/powerpc/kexec/file_load.c b/arch/powerpc/kexec/file_load.c
> index 4284f76cbef5..e1c08050286d 100644
> --- a/arch/powerpc/kexec/file_load.c
> +++ b/arch/powerpc/kexec/file_load.c
> @@ -23,38 +23,41 @@
>   #define SLAVE_CODE_SIZE		256	/* First 0x100 bytes */
>   
>   /**
> - * setup_kdump_cmdline - Prepend "elfcorehdr=<addr> " to command line
> + * setup_kdump_cmdline - Prepend "<name>=<addr> " to command line
>    *                       of kdump kernel for exporting the core.
>    * @image:               Kexec image
>    * @cmdline:             Command line parameters to update.
>    * @cmdline_len:         Length of the cmdline parameters.
> + * @name:                Name e.g elfcorehdr.
> + * @addr:                Memory address.
>    *
>    * kdump segment must be setup before calling this function.
>    *
>    * Returns new cmdline buffer for kdump kernel on success, NULL otherwise.
>    */
>   char *setup_kdump_cmdline(struct kimage *image, char *cmdline,
> -			  unsigned long cmdline_len)
> +			  unsigned long cmdline_len,
> +			  char *name, unsigned long addr)
>   {
> -	int elfcorehdr_strlen;
> +	unsigned long parameter_len;
>   	char *cmdline_ptr;
>   
>   	cmdline_ptr = kzalloc(COMMAND_LINE_SIZE, GFP_KERNEL);
>   	if (!cmdline_ptr)
>   		return NULL;
>   
> -	elfcorehdr_strlen = sprintf(cmdline_ptr, "elfcorehdr=0x%lx ",
> -				    image->elf_load_addr);
> +	parameter_len = sprintf(cmdline_ptr, "%s=0x%lx ", name, addr);
>   
> -	if (elfcorehdr_strlen + cmdline_len > COMMAND_LINE_SIZE) {
> -		pr_err("Appending elfcorehdr=<addr> exceeds cmdline size\n");
> +	if (parameter_len + cmdline_len > COMMAND_LINE_SIZE) {
> +		pr_err("Appending %s=<addr> exceeds cmdline size\n", name);
>   		kfree(cmdline_ptr);
>   		return NULL;
>   	}
>   
> -	memcpy(cmdline_ptr + elfcorehdr_strlen, cmdline, cmdline_len);
> +	memcpy(cmdline_ptr + parameter_len, cmdline, cmdline_len);
>   	// Ensure it's nul terminated
>   	cmdline_ptr[COMMAND_LINE_SIZE - 1] = '\0';
> +	kfree(cmdline);

When setup_kdump_cmdline() is called for elfcorehdr, cmdline holds the
same pointer as image->cmdline_buf. Freeing it here may therefore
cause issues, right?

Currently, image->cmdline_buf is not used after calling the
architecture-specific load function (elf64_load on powerpc).
However, kimage_file_post_load_cleanup() later calls kfree() on
the same address.

>   	return cmdline_ptr;
>   }
>   
>
> base-commit: ccd1cdca5cd433c8a5dff78b69a79b31d9b77ee1