Re: [PATCH 2/2] x86/sev: Make SEV_STATUS available via SYSFS

[Tom Lendacky]

On 3/12/25 09:41, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@xxxxxxx>
> 
> Current user-space tooling which needs access to the SEV_STATUS MSR is
> using the MSR module. The use of this module poses a security risk in
> any trusted execution environment and is generally discouraged.
> 
> Instead, provide an file in SYSFS in the /sys/hypervisor/sev/
> directory to provide the value of the SEV_STATUS MSR to user-space.
> 
> Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
> ---
>  Documentation/ABI/testing/sysfs-hypervisor | 5 +++++
>  arch/x86/coco/sev/core.c                   | 9 +++++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-hypervisor b/Documentation/ABI/testing/sysfs-hypervisor
> index aca8b02c878c..54c80899c19c 100644
> --- a/Documentation/ABI/testing/sysfs-hypervisor
> +++ b/Documentation/ABI/testing/sysfs-hypervisor
> @@ -1,5 +1,6 @@
>  What:		/sys/devices/system/cpu/sev
>  		/sys/devices/system/cpu/sev/vmpl
> +		/sys/devices/system/cpu/sev/sev_status
>  Date:		May 2024
>  Contact:	Linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx>
>  Description:	Secure Encrypted Virtualization (SEV) information
> @@ -8,3 +9,7 @@ Description:	Secure Encrypted Virtualization (SEV) information
>  
>  		vmpl: Reports the Virtual Machine Privilege Level (VMPL) at which
>  		      the SEV-SNP guest is running.
> +
> +		sev_status: Reports the value of the SEV_STATUS MSR which
> +		            enumerates the enabled features of an SEV-SNP
> +			    environment.
> diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> index 51a04a19449b..3e834ce9badc 100644
> --- a/arch/x86/coco/sev/core.c
> +++ b/arch/x86/coco/sev/core.c
> @@ -2678,10 +2678,19 @@ static ssize_t vmpl_show(struct kobject *kobj,
>  	return sysfs_emit(buf, "%d\n", snp_vmpl);
>  }
>  
> +static ssize_t sev_status_show(struct kobject *kobj,
> +			       struct kobj_attribute *attr, char *buf)
> +{
> +	return sysfs_emit(buf, "%llx\n", sev_status);

Should it be prefixed with '0x'? That would make use of functions like
atoi() and strtol() easier.

Thanks,
Tom

> +}
> +
>  static struct kobj_attribute vmpl_attr = __ATTR_RO(vmpl);
> +static struct kobj_attribute sev_status_attr = __ATTR_RO(sev_status);
> +
>  
>  static struct attribute *vmpl_attrs[] = {
>  	&vmpl_attr.attr,
> +	&sev_status_attr.attr,
>  	NULL
>  };
>