Re: [PATCH v6 6/6] drivers/node: Show in sysfs node's crypto capabilities

["Limonciello, Mario" <mario.limonciello@amd.com>]

On 2/3/2022 10:43, Martin Fernandez wrote:
> Show in each node in sysfs if its memory is able to do be encrypted by
> the CPU, ie. if all its memory is marked with EFI_MEMORY_CPU_CRYPTO in
> the EFI memory map.
> 
> Signed-off-by: Martin Fernandez <martin.fernandez@eclypsium.com>
> ---
>   Documentation/ABI/testing/sysfs-devices-node | 10 ++++++++++
>   drivers/base/node.c                          | 10 ++++++++++
>   2 files changed, 20 insertions(+)
>   create mode 100644 Documentation/ABI/testing/sysfs-devices-node
> 
> diff --git a/Documentation/ABI/testing/sysfs-devices-node b/Documentation/ABI/testing/sysfs-devices-node
> new file mode 100644
> index 000000000000..0d1fd86c9faf
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-devices-node
> @@ -0,0 +1,10 @@
> +What:		/sys/devices/system/node/nodeX/crypto_capable
> +Date:		February 2022
> +Contact:	Martin Fernandez <martin.fernandez@eclypsium.com>
> +Users:		fwupd (https://fwupd.org)
> +Description:
> +		This value is 1 if all system memory in this node is
> +		marked with EFI_MEMORY_CPU_CRYPTO, indicating that the
> +		system memory is capable of being protected with the
> +		CPU’s memory cryptographic capabilities. It is 0
> +		otherwise.
> \ No newline at end of file
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 87acc47e8951..dabaed997ecd 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -560,11 +560,21 @@ static ssize_t node_read_distance(struct device *dev,
>   }
>   static DEVICE_ATTR(distance, 0444, node_read_distance, NULL);
>   
> +static ssize_t crypto_capable_show(struct device *dev,
> +				   struct device_attribute *attr, char *buf)
> +{
> +	struct pglist_data *pgdat = NODE_DATA(dev->id);
> +
> +	return sysfs_emit(buf, "%d\n", pgdat->crypto_capable);

As there is interest in seeing these capabilities from userspace, it 
seems like a logical time to also expose a `crypto_active` attribute.

Then userspace can make a judgement call if the system supports crypto 
memory (`crypto_capable`) and then also whether or not it's been turned 
on (`crypto_active`).

`crypto_active` could be detected with some existing support in the 
kernel of `mem_encrypt_active()`.  This will then work for a variety of 
architectures too that offer `mem_encrypt_active()`.

As it stands today the only reliable way to tell from userspace (at 
least for AMD's x86 implementation) is by grepping the system log for 
the line "AMD Memory Encryption Features active".

> +}
> +static DEVICE_ATTR_RO(crypto_capable);
> +
>   static struct attribute *node_dev_attrs[] = {
>   	&dev_attr_meminfo.attr,
>   	&dev_attr_numastat.attr,
>   	&dev_attr_distance.attr,
>   	&dev_attr_vmstat.attr,
> +	&dev_attr_crypto_capable.attr,
>   	NULL
>   };
>