linux-kernel - Re: [PATCH v4 2/7] crash_dump: make dm crypt keys persist for the kdump kernel

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Date: Wed, 5 Jun 2024 16:22:12 +0800
From: Baoquan He <bhe@...hat.com>
To: Coiby Xu <coxu@...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>, Kees Cook <keescook@...omium.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	"open list:KERNEL HARDENING (not covered by other areas):Keyword:b__counted_byb" <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH v4 2/7] crash_dump: make dm crypt keys persist for the
 kdump kernel

On 05/23/24 at 01:04pm, Coiby Xu wrote:
.....
> diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
> new file mode 100644
> index 000000000000..78809189084a
> --- /dev/null
> +++ b/kernel/crash_dump_dm_crypt.c
> @@ -0,0 +1,113 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <keys/user-type.h>
> +#include <linux/crash_dump.h>
> +
> +#define KEY_NUM_MAX 128
> +#define KEY_SIZE_MAX 256
> +
> +// The key scription has the format: cryptsetup:UUID 11+36+1(NULL)=48
> +#define KEY_DESC_LEN 48
> +
> +static char *STATE_STR[] = {"fresh", "initialized", "recorded", "loaded"};
> +static enum STATE_ENUM {
> +	FRESH = 0,
> +	INITIALIZED,
> +	RECORDED,
> +	LOADED,
> +} state;
> +
> +static unsigned int key_count;
> +static size_t keys_header_size;

These two global variables seems not so necessary. Please see comment at
below.

> +
> +struct dm_crypt_key {
> +	unsigned int key_size;
> +	char key_desc[KEY_DESC_LEN];
> +	u8 data[KEY_SIZE_MAX];
> +};
> +
> +static struct keys_header {
> +	unsigned int key_count;
                     ~~~~~~~~
                     This is the max number a system have from init();
You can add one field member to record how many key slots have been
used.
> +	struct dm_crypt_key keys[] __counted_by(key_count);
> +} *keys_header;

Maybe we can rearrange the keys_header like below, the name may not be
very appropriate though.

static struct keys_header {
	unsigned int max_key_slots;
	unsigned int used_key_slots;
	struct dm_crypt_key keys[] __counted_by(key_count);
} *keys_header;

>

> +
> +static size_t get_keys_header_size(struct keys_header *keys_header,
> +				   size_t key_count)
> +{
> +	return struct_size(keys_header, keys, key_count);
> +}

I personally don't think get_keys_header_size is so necessary. If we
have to keep it, may be we can remove the global variable
keys_header_size, we can call get_keys_header_size() and use local
variable to record the value instead.