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

Limonciello, Mario
2022-02-04T03:47:12Z

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
> };
>