Re: [PATCH v2 8/9] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if CONFIG_CRASH_HOTPLUG enabled

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

On 02/05/26 05:13, Coiby Xu wrote:
> If CONFIG_CRASH_HOTPLUG is enabled, dm-crypt keys saved to reserved
> memory will be took 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 CONFIG_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 |  9 ++++++---
>   kernel/crash_dump_dm_crypt.c              | 14 +++++++++++---
>   2 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> index 7587caadbae1..73f2e9500c60 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
> @@ -593,7 +594,9 @@ with /sys/kernel/config/crash_dm_crypt_keys for setup,
>   
>       # To support CPU/memory hot-plugging, reuse keys already saved to reserved
>       # memory
> -    echo true > /sys/kernel/config/crash_dm_crypt_key/reuse
> +    # Note if CONFIG_CRASH_HOTPLUG is enabled, this API is totally unnecessary
> +    # thus will be disabled.
> +    echo true > /sys/kernel/config/crash_dm_crypt_keys/reuse
>   
>   2. Load the dump-capture kernel
>   
> diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
> index 36e51807d94f..7a7cae17f578 100644
> --- a/kernel/crash_dump_dm_crypt.c
> +++ b/kernel/crash_dump_dm_crypt.c
> @@ -304,6 +304,11 @@ static ssize_t config_keys_reuse_store(struct config_item *item,
>   	bool val;
>   	int r;
>   
> +	if (IS_ENABLED(CONFIG_CRASH_HOTPLUG)) {
> +		pr_info("CONFIG_CRASH_HOTPLUG already enabled");
> +		return -EINVAL;
> +	}
> +

Deciding this solely at compile time can create issues. For example, the 
kernel
may be built with CONFIG_CRASH_HOTPLUG, but if kexec tool loads the kdump
kernel using the kexec_load system call without hotplug support, it can
cause problems. It is rare but possible.

How about this:

#ifdef CONFIG_CRASH_HOTPLUG
     if (kexec_crash_image->hotplug_support) {
pr_info("crash image is loaded with hotplug support\n");return -EINVAL;
     }
#endif

This code should be placed after validating kexec_crash_image.


- Sourabh Jain

>   	if (!kexec_crash_image || !kexec_crash_image->dm_crypt_keys_addr) {
>   		pr_info("dm-crypt keys haven't be saved to crash-reserved memory\n");
>   		return -EINVAL;
> @@ -486,15 +491,18 @@ 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);
>   		keys_header = NULL;
>   	}
>   
> +	if (IS_ENABLED(CONFIG_CRASH_HOTPLUG))
> +		image->dm_crypt_keys_addr = 0;
> +
>   	if (mutex_is_locked(&config_keys_subsys.su_mutex))
>   		mutex_unlock(&config_keys_subsys.su_mutex);
>   }