Re: [PATCH v3 09/10] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if crash hotplug supported

[Sourabh Jain <sourabhjain@linux.ibm.com>]

On 29/07/26 09:06, Coiby Xu wrote:
> If crash hotplug is supported, dm-crypt keys saved to reserved memory
> will be taken care of automatically. Thus it doesn't make sense to use
> configfs/crash_dm_crypt_key/reuse. Reserving image->dm_crypt_keys_addr
> is also unnecessary. Currently x86_64 and ppc64le have implemented
> crash hotplug feature.
>
> Also update the doc accordingly. Note two doc issues are fixed as well.
>
> Fixes: 9ebfa8dcaea7 ("crash_dump: reuse saved dm crypt keys for CPU/memory hot-plugging")
> Signed-off-by: Coiby Xu <coiby.xu@gmail.com>
> ---
>   Documentation/admin-guide/kdump/kdump.rst | 16 ++++++++++------
>   kernel/crash_dump_dm_crypt.c              | 23 ++++++++++++++++++++---
>   2 files changed, 30 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> index 7587caadbae1..0bf2eb100a05 100644
> --- a/Documentation/admin-guide/kdump/kdump.rst
> +++ b/Documentation/admin-guide/kdump/kdump.rst
> @@ -577,9 +577,10 @@ 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
> -    mkdir /sys/kernel/config/crash_dm_crypt_keys/7d26b7b4-e342-4d2d-b660-7426b0996720
> +    VOL1_UUID=7d26b7b4-e342-4d2d-b660-7426b0996720
> +    mkdir /sys/kernel/config/crash_dm_crypt_keys/$VOL1_UUID
>       # Add key #1's description
> -    echo cryptsetup:7d26b7b4-e342-4d2d-b660-7426b0996720 > /sys/kernel/config/crash_dm_crypt_keys/description
> +    echo cryptsetup:$VOL1_UUID > /sys/kernel/config/crash_dm_crypt_keys/$VOL1_UUID/description
>   
>       # how many keys do we have now?
>       cat /sys/kernel/config/crash_dm_crypt_keys/count
> @@ -591,15 +592,18 @@ with /sys/kernel/config/crash_dm_crypt_keys for setup,
>       cat /sys/kernel/config/crash_dm_crypt_keys/count
>       2
>   
> -    # To support CPU/memory hot-plugging, reuse keys already saved to reserved
> -    # memory
> -    echo true > /sys/kernel/config/crash_dm_crypt_key/reuse
> -
>   2. Load the dump-capture kernel
>   
>   3. After the dump-capture kerne get booted, restore the keys to user keyring
>      echo yes > /sys/kernel/crash_dm_crypt_keys/restore
>   
> +For CPU/memory hot-plugging, you can reuse keys already saved to reserved
> +memory before reloading the kdump image,
> +    echo true > /sys/kernel/config/crash_dm_crypt_keys/reuse
> +
> +Note if crash hotplug is supported, this API is totally unnecessary thus will
> +be disabled automatically.
> +
>   Contact
>   =======
>   
> diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
> index b5b78656cf06..46d6b31c3ca4 100644
> --- a/kernel/crash_dump_dm_crypt.c
> +++ b/kernel/crash_dump_dm_crypt.c
> @@ -310,6 +310,15 @@ static ssize_t config_keys_reuse_show(struct config_item *item, char *page)
>   	return sysfs_emit(page, "%d\n", is_dm_key_reused);
>   }
>   
> +static bool crash_hotplug_support(struct kimage *image)
> +{
> +#ifdef CONFIG_CRASH_HOTPLUG
> +	return image->hotplug_support;

I don't think it is good idea to access kexec_crash_image properties without
holding the kexec lock.

Also, would it make sense to move this API somewhere else?

- Sourabh Jain

> +#else
> +	return false;
> +#endif
> +}
> +
>   static ssize_t config_keys_reuse_store(struct config_item *item,
>   					   const char *page, size_t count)
>   {
> @@ -317,6 +326,11 @@ static ssize_t config_keys_reuse_store(struct config_item *item,
>   	bool val;
>   	int r;
>   
> +	if (kexec_crash_image && crash_hotplug_support(kexec_crash_image)) {
> +		pr_debug("Crash hotplug supported\n");
> +		return -EINVAL;
> +	}
> +
>   	if (!kexec_crash_image || !kexec_crash_image->dm_crypt_keys_addr) {
>   		pr_debug("dm-crypt keys haven't be saved to crash-reserved memory\n");
>   		return -EINVAL;
> @@ -513,9 +527,9 @@ int crash_load_dm_crypt_keys(struct kimage *image)
>   void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
>   {
>   	/*
> -	 * For CPU/memory hot-plugging, the kdump image will be reloaded. Prevent
> -	 * keys_header from being cleaned up during unloading when
> -	 * is_dm_key_reused=true
> +	 * For CPU/memory hot-plugging without CONFIG_CRASH_HOTPLUG, the whole kdump
> +	 * image will be reloaded. Prevent keys_header from being cleaned up during
> +	 * unloading when is_dm_key_reused=true
>   	 */
>   	if (!is_dm_key_reused) {
>   		kfree_sensitive(keys_header);
> @@ -526,6 +540,9 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image)
>   		mutex_unlock(&config_keys_subsys.su_mutex);
>   		mutex_acquired = false;
>   	}
> +
> +	if (crash_hotplug_support(image))
> +		image->dm_crypt_keys_addr = 0;
>   }
>   
>   static int __init configfs_dmcrypt_keys_init(void)