[PATCH v2] powerpc/kdump: pass dm-crypt keys to kdump kernel
Sourabh Jain
sourabhjain at linux.ibm.com
Wed Jan 7 20:02:41 AEDT 2026
On 06/01/26 13:10, Coiby Xu wrote:
> 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 PowerPC, we only need to let 1st kernel
> 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.
>
> Note to avoid a building failure [2] caused by undeclared function
> crash_load_dm_crypt_keys when CONFIG_CRASH_DUMP is not enabled,
> realign the function declaration with CONFIG_CRASH_DM_CRYPT.
>
> [1] https://lore.kernel.org/all/20250502011246.99238-1-coxu@redhat.com/
> [2] https://lore.kernel.org/oe-kbuild-all/202512272218.ghBaSjzO-lkp@intel.com/
>
> Cc: Thomas Staudt <tstaudt at de.ibm.com>
> 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: Sourabh Jain <sourabhjain at linux.ibm.com>
> Signed-off-by: Coiby Xu <coxu at redhat.com>
> ---
> v2:
> - fix double kfree issue [Sourabh]
> - corretly kfree old modified_cmdline
> - use imperative mood for commit message
> - fix a compiling error caught by kernel test robot
>
> arch/powerpc/include/asm/kexec.h | 3 ++-
> arch/powerpc/kexec/elf_64.c | 27 ++++++++++++++++++++++++++-
> arch/powerpc/kexec/file_load.c | 18 ++++++++++--------
> include/linux/crash_core.h | 14 +++++++-------
> 4 files changed, 45 insertions(+), 17 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..995d7e8e98e1 100644
> --- a/arch/powerpc/kexec/elf_64.c
> +++ b/arch/powerpc/kexec/elf_64.c
> @@ -81,13 +81,38 @@ 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;
I have a limited understanding of the new dm-crypt keys, but the way they
are loaded and the additional command-line options added for the kdump
kernel look good to me.
Feel free to add:
Acked-by: Sourabh Jain <sourabhjain at linux.ibm.com>
> +
> + 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);
> + kfree(cmdline);
> + 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..9964c57785f5 100644
> --- a/arch/powerpc/kexec/file_load.c
> +++ b/arch/powerpc/kexec/file_load.c
> @@ -23,36 +23,38 @@
> #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';
> return cmdline_ptr;
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index d35726d6a415..e128270c703f 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -34,13 +34,6 @@ static inline void arch_kexec_protect_crashkres(void) { }
> static inline void arch_kexec_unprotect_crashkres(void) { }
> #endif
>
> -#ifdef CONFIG_CRASH_DM_CRYPT
> -int crash_load_dm_crypt_keys(struct kimage *image);
> -ssize_t dm_crypt_keys_read(char *buf, size_t count, u64 *ppos);
> -#else
> -static inline int crash_load_dm_crypt_keys(struct kimage *image) {return 0; }
> -#endif
> -
> #ifndef arch_crash_handle_hotplug_event
> static inline void arch_crash_handle_hotplug_event(struct kimage *image, void *arg) { }
> #endif
> @@ -96,4 +89,11 @@ static inline void crash_save_cpu(struct pt_regs *regs, int cpu) {};
> static inline int kimage_crash_copy_vmcoreinfo(struct kimage *image) { return 0; };
> #endif /* CONFIG_CRASH_DUMP*/
>
> +#ifdef CONFIG_CRASH_DM_CRYPT
> +int crash_load_dm_crypt_keys(struct kimage *image);
> +ssize_t dm_crypt_keys_read(char *buf, size_t count, u64 *ppos);
> +#else
> +static inline int crash_load_dm_crypt_keys(struct kimage *image) { return 0; }
> +#endif
> +
> #endif /* LINUX_CRASH_CORE_H */
>
> base-commit: 7f98ab9da046865d57c102fd3ca9669a29845f67
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