x86/crash: pass dm crypt keys to kdump kernel

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 key to kdump kernel.

Link: https://lkml.kernel.org/r/20250502011246.99238-8-coxu@redhat.com
Signed-off-by: Coiby Xu <coxu@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: "Daniel P. Berrange" <berrange@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Jan Pazdziora <jpazdziora@redhat.com>
Cc: Liu Pingfan <kernelfans@gmail.com>
Cc: Milan Broz <gmazyland@gmail.com>
Cc: Ondrej Kozina <okozina@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: coiby

Documentation/admin-guide/kdump/kdump.rst

@@ -551,8 +551,8 @@ Write the dump file to encrypted disk volume
 ============================================
 
 CONFIG_CRASH_DM_CRYPT can be enabled to support saving the dump file to an
-encrypted disk volume. User space can interact with
-/sys/kernel/config/crash_dm_crypt_keys for setup,
+encrypted disk volume (only x86_64 supported for now). User space can interact
+with /sys/kernel/config/crash_dm_crypt_keys for setup,
 
 1. Tell the first kernel what logon keys are needed to unlock the disk volumes,
     # Add key #1

arch/x86/kernel/crash.c

@@ -278,6 +278,7 @@ static int memmap_exclude_ranges(struct kimage *image, struct crash_mem *cmem,
 				 unsigned long long mend)
 {
 	unsigned long start, end;
+	int ret;
 
 	cmem->ranges[0].start = mstart;
 	cmem->ranges[0].end = mend;
@@ -286,22 +287,43 @@ static int memmap_exclude_ranges(struct kimage *image, struct crash_mem *cmem,
 	/* Exclude elf header region */
 	start = image->elf_load_addr;
 	end = start + image->elf_headers_sz - 1;
-	return crash_exclude_mem_range(cmem, start, end);
+	ret = crash_exclude_mem_range(cmem, start, end);
+
+	if (ret)
+		return ret;
+
+	/* Exclude dm crypt keys region */
+	if (image->dm_crypt_keys_addr) {
+		start = image->dm_crypt_keys_addr;
+		end = start + image->dm_crypt_keys_sz - 1;
+		return crash_exclude_mem_range(cmem, start, end);
+	}
+
+	return ret;
 }
 
 /* Prepare memory map for crash dump kernel */
 int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
 {
+	unsigned int nr_ranges = 0;
 	int i, ret = 0;
 	unsigned long flags;
 	struct e820_entry ei;
 	struct crash_memmap_data cmd;
 	struct crash_mem *cmem;
 
-	cmem = vzalloc(struct_size(cmem, ranges, 1));
+	/*
+	 * Using random kexec_buf for passing dm crypt keys may cause a range
+	 * split. So use two slots here.
+	 */
+	nr_ranges = 2;
+	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
 	if (!cmem)
 		return -ENOMEM;
 
+	cmem->max_nr_ranges = nr_ranges;
+	cmem->nr_ranges = 0;
+
 	memset(&cmd, 0, sizeof(struct crash_memmap_data));
 	cmd.params = params;
 

arch/x86/kernel/kexec-bzimage64.c

@@ -27,6 +27,8 @@
 #include <asm/kexec-bzimage64.h>
 
 #define MAX_ELFCOREHDR_STR_LEN	30	/* elfcorehdr=0x<64bit-value> */
+#define MAX_DMCRYPTKEYS_STR_LEN	31	/* dmcryptkeys=0x<64bit-value> */
+
 
 /*
  * Defines lowest physical address for various segments. Not sure where
@@ -76,6 +78,10 @@ static int setup_cmdline(struct kimage *image, struct boot_params *params,
 	if (image->type == KEXEC_TYPE_CRASH) {
 		len = sprintf(cmdline_ptr,
 			"elfcorehdr=0x%lx ", image->elf_load_addr);
+
+		if (image->dm_crypt_keys_addr != 0)
+			len += sprintf(cmdline_ptr + len,
+					"dmcryptkeys=0x%lx ", image->dm_crypt_keys_addr);
 	}
 	memcpy(cmdline_ptr + len, cmdline, cmdline_len);
 	cmdline_len += len;
@@ -441,6 +447,19 @@ static void *bzImage64_load(struct kimage *image, char *kernel,
 		ret = crash_load_segments(image);
 		if (ret)
 			return ERR_PTR(ret);
+		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 &&
+		    cmdline_len + MAX_ELFCOREHDR_STR_LEN + MAX_DMCRYPTKEYS_STR_LEN >
+			    header->cmdline_size) {
+			pr_err("Appending dmcryptkeys=<addr> to command line exceeds maximum allowed length\n");
+			return ERR_PTR(-EINVAL);
+		}
 	}
 #endif
 
@@ -468,6 +487,8 @@ static void *bzImage64_load(struct kimage *image, char *kernel,
 	efi_map_sz = efi_get_runtime_map_size();
 	params_cmdline_sz = sizeof(struct boot_params) + cmdline_len +
 				MAX_ELFCOREHDR_STR_LEN;
+	if (image->dm_crypt_keys_addr)
+		params_cmdline_sz += MAX_DMCRYPTKEYS_STR_LEN;
 	params_cmdline_sz = ALIGN(params_cmdline_sz, 16);
 	kbuf.bufsz = params_cmdline_sz + ALIGN(efi_map_sz, 16) +
 				sizeof(struct setup_data) +