Date: Fri, 24 May 2024 15:38:18 +0800
From: Coiby Xu <coxu@...hat.com>
To: Baoquan He <bhe@...hat.com>
Cc: kexec@...ts.infradead.org, Ondrej Kozina <okozina@...hat.com>, 
	Milan Broz <gmazyland@...il.com>, Thomas Staudt <tstaudt@...ibm.com>, 
	Daniel P . Berrangé <berrange@...hat.com>, Kairui Song <ryncsn@...il.com>, 
	. Jan Pazdziora <jpazdziora@...hat.com>, Pingfan Liu <kernelfans@...il.com>, 
	Dave Young <dyoung@...hat.com>, linux-kernel@...r.kernel.org, x86@...nel.org, 
	Dave Hansen <dave.hansen@...el.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, 
	Vivek Goyal <vgoyal@...hat.com>, Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [PATCH v3 3/7] crash_dump: store dm keys in kdump reserved memory

On Tue, May 21, 2024 at 11:42:52AM +0800, Baoquan He wrote:
>On 04/25/24 at 06:04pm, Coiby Xu wrote:
>> When the kdump kernel image and initrd are loaded, the dm crypts keys
>> will be read from keyring and then stored in kdump reserved memory.
>>
>> Signed-off-by: Coiby Xu <coxu@...hat.com>
>> ---
>>  include/linux/crash_core.h   |  3 ++
>>  include/linux/crash_dump.h   |  2 +
>>  include/linux/kexec.h        |  4 ++
>>  kernel/crash_dump_dm_crypt.c | 87 ++++++++++++++++++++++++++++++++++++
>>  4 files changed, 96 insertions(+)
>>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index 98825b7e0ea6..1f3d5a4fa6c1 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -37,6 +37,9 @@ static inline void arch_kexec_unprotect_crashkres(void) { }
>>  #ifdef CONFIG_CRASH_DM_CRYPT
>>  int crash_sysfs_dm_crypt_keys_read(char *buf);
>>  int crash_sysfs_dm_crypt_keys_write(const char *buf, size_t count);
>> +int crash_load_dm_crypt_keys(struct kimage *image);
>> +#else
>> +static inline int crash_load_dm_crypt_keys(struct kimage *image) {return 0; }
>>  #endif
>>
>>  #ifndef arch_crash_handle_hotplug_event
>> diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
>> index acc55626afdc..dfd8e4fe6129 100644
>> --- a/include/linux/crash_dump.h
>> +++ b/include/linux/crash_dump.h
>> @@ -15,6 +15,8 @@
>>  extern unsigned long long elfcorehdr_addr;
>>  extern unsigned long long elfcorehdr_size;
>>
>> +extern unsigned long long dm_crypt_keys_addr;
>> +
>>  #ifdef CONFIG_CRASH_DUMP
>>  extern int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size);
>>  extern void elfcorehdr_free(unsigned long long addr);
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index fc1e20d565d5..b6cedce66828 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -368,6 +368,10 @@ struct kimage {
>>  	void *elf_headers;
>>  	unsigned long elf_headers_sz;
>>  	unsigned long elf_load_addr;
>> +
>> +	/* dm crypt keys buffer */
>> +	unsigned long dm_crypt_keys_addr;
>> +	unsigned long dm_crypt_keys_sz;
>>  };
>>
>>  /* kexec interface functions */
>> diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
>> index 847499cdcd42..b9997fb53351 100644
>> --- a/kernel/crash_dump_dm_crypt.c
>> +++ b/kernel/crash_dump_dm_crypt.c
>> @@ -1,4 +1,6 @@
>>  // SPDX-License-Identifier: GPL-2.0-only
>> +#include <linux/key.h>
>> +#include <linux/keyctl.h>
>>  #include <keys/user-type.h>
>>  #include <linux/crash_dump.h>
>>
>> @@ -111,3 +113,88 @@ int crash_sysfs_dm_crypt_keys_read(char *buf)
>>  	return sprintf(buf, "%s\n", STATE_STR[state]);
>>  }
>>  EXPORT_SYMBOL(crash_sysfs_dm_crypt_keys_read);
>> +
>> +static int read_key_from_user_keying(struct dm_crypt_key *dm_key)
>> +{
>> +	const struct user_key_payload *ukp;
>> +	struct key *key;
>> +
>> +	pr_debug("Requesting key %s", dm_key->key_desc);
>> +	key = request_key(&key_type_logon, dm_key->key_desc, NULL);
>> +
>> +	if (IS_ERR(key)) {
>> +		pr_warn("No such key %s\n", dm_key->key_desc);
>> +		return PTR_ERR(key);
>> +	}
>> +
>> +	ukp = user_key_payload_locked(key);
>> +	if (!ukp)
>> +		return -EKEYREVOKED;
>> +
>> +	memcpy(dm_key->data, ukp->data, ukp->datalen);
>> +	dm_key->key_size = ukp->datalen;
>> +	pr_debug("Get dm crypt key (size=%u) %s: %8ph\n", dm_key->key_size,
>> +		 dm_key->key_desc, dm_key->data);
>> +	return 0;
>> +}
>> +
>> +static int build_keys_header(void)
>> +{
>> +	int i, r;
>> +
>> +	for (i = 0; i < key_count; i++) {
>> +		r = read_key_from_user_keying(&keys_header->keys[i]);
>> +		if (r != 0) {
>> +			pr_err("Failed to read key %s\n", keys_header->keys[i].key_desc);
>> +			return r;
>> +		}
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +int crash_load_dm_crypt_keys(struct kimage *image)
>> +{
>> +	struct kexec_buf kbuf = {
>> +		.image = image,
>> +		.buf_min = 0,
>> +		.buf_max = ULONG_MAX,
>> +		.top_down = false,
>> +		.random = true,
>> +	};
>> +
>> +	int r;
>> +
>> +	if (state == FRESH)
>> +		return 0;
>> +
>> +	if (key_count != keys_header->key_count) {
>> +		pr_err("Only record %u keys (%u in total)\n", key_count,
>> +		       keys_header->key_count);
>> +		return -EINVAL;
>> +	}
>> +
>> +	image->dm_crypt_keys_addr = 0;
>> +	r = build_keys_header();
>> +	if (r)
>> +		return r;
>> +
>> +	kbuf.buffer = keys_header;
>> +	kbuf.bufsz = keys_header_size;
>> +
>> +	kbuf.memsz = kbuf.bufsz;
>> +	kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
>> +	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>> +	r = kexec_add_buffer(&kbuf);
>> +	if (r) {
>> +		vfree((void *)kbuf.buffer);
>> +		return r;
>> +	}
>> +	state = LOADED;
>> +	image->dm_crypt_keys_addr = kbuf.mem;
>> +	image->dm_crypt_keys_sz = kbuf.bufsz;
>> +	pr_debug("Loaded dm crypt keys at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
>> +		 image->dm_crypt_keys_addr, kbuf.bufsz, kbuf.bufsz);
>
>Please use kexec_dprintk() instead to print debugging message.

Thanks for pointing me to kexec_dprintk! I'll use kexec_dprintk.

>And you don't worry this printing will leak the key position and the
>information?

Thanks for raising this concern! I'll remove the key position info as it
seems kernel dyndbg can be easily enabled.

-- 
Best regards,
Coiby

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