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

[Coiby Xu]

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 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>
Signed-off-by: Coiby Xu <coxu at 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);
 	return cmdline_ptr;
 }
 

base-commit: ccd1cdca5cd433c8a5dff78b69a79b31d9b77ee1
-- 
2.52.0