linux-kernel - Re: [PATCH v3 4/7] crash_dump: reuse saved dm crypt keys for CPU/memory hot-plugging

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Date: Tue, 21 May 2024 11:48:49 +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>
Subject: Re: [PATCH v3 4/7] crash_dump: reuse saved dm crypt keys for
 CPU/memory hot-plugging

On 04/25/24 at 06:04pm, Coiby Xu wrote:
> When there is CPU/memory hot-plugging, the kdump kernel image and initrd
> will be reloaded. The user space can write the "reuse" command to
> /sys/kernel/crash_dm_crypt_key so the stored keys can be re-saved again.
> 
> Note currently only x86 (commit ea53ad9cf73b ("x86/crash: add x86 crash
> hotplug support")) and ppc (WIP) supports the new infrastructure
> (commit 247262756121 ("crash: add generic infrastructure for crash
> hotplug support")). If the new infrastructure get extended to all arches,
> this patch can be dropped.
> 
> Signed-off-by: Coiby Xu <coxu@...hat.com>
> ---
>  kernel/crash_dump_dm_crypt.c | 30 ++++++++++++++++++++++++++----
>  1 file changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
> index b9997fb53351..6ac1fabdb6cb 100644
> --- a/kernel/crash_dump_dm_crypt.c
> +++ b/kernel/crash_dump_dm_crypt.c
> @@ -10,12 +10,13 @@
>  // 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 char *STATE_STR[] = {"fresh", "initialized", "recorded", "loaded", "reuse"};
>  enum STATE_ENUM {
>  	FRESH = 0,
>  	INITIALIZED,
>  	RECORDED,
>  	LOADED,
> +	REUSE,
>  } state;
>  
>  static unsigned int key_count;
> @@ -90,12 +91,31 @@ static int record_key_desc(const char *buf, struct dm_crypt_key *dm_key)
>  	return 0;
>  }
>  
> +static void get_keys_from_kdump_reserved_memory(void)
> +{
> +	struct keys_header *keys_header_loaded;
> +
> +	arch_kexec_unprotect_crashkres();

I don't see the corresponging arch_kexec_protect_crashkres() in the
following flow. Aren't they a pair when used?

> +
> +	keys_header_loaded = kmap_local_page(pfn_to_page(
> +		kexec_crash_image->dm_crypt_keys_addr >> PAGE_SHIFT));
> +
> +	memcpy(keys_header, keys_header_loaded, keys_header_size);
> +	kunmap_local(keys_header_loaded);
> +	state = RECORDED;
> +}
> +
>  static int process_cmd(const char *buf, size_t count)
>  {
>  	if (strncmp(buf, "init ", 5) == 0)
>  		return init(buf);
>  	else if (strncmp(buf, "record ", 7) == 0)
>  		return record_key_desc(buf, &keys_header->keys[key_count]);
> +	else if (!strcmp(buf, "reuse")) {
> +		state = REUSE;
> +		get_keys_from_kdump_reserved_memory();
> +		return 0;
> +	}
>  
>  	return -EINVAL;
>  }
> @@ -175,9 +195,11 @@ int crash_load_dm_crypt_keys(struct kimage *image)
>  	}
>  
>  	image->dm_crypt_keys_addr = 0;
> -	r = build_keys_header();
> -	if (r)
> -		return r;
> +	if (state != REUSE) {
> +		r = build_keys_header();
> +		if (r)
> +			return r;
> +	}
>  
>  	kbuf.buffer = keys_header;
>  	kbuf.bufsz = keys_header_size;
> -- 
> 2.44.0
>