Commit fce96cf0 authored by Brijesh Singh's avatar Brijesh Singh Committed by Borislav Petkov
Browse files

virt: Add SEV-SNP guest driver 



The SEV-SNP specification provides the guest a mechanism to communicate
with the PSP without risk from a malicious hypervisor who wishes to
read, alter, drop or replay the messages sent. The driver uses
snp_issue_guest_request() to issue GHCB SNP_GUEST_REQUEST or
SNP_EXT_GUEST_REQUEST NAE events to submit the request to PSP.

The PSP requires that all communication should be encrypted using key
specified through a struct snp_guest_platform_data descriptor.

Userspace can use SNP_GET_REPORT ioctl() to query the guest attestation
report.

See SEV-SNP spec section Guest Messages for more details.

  [ bp: Remove the "what" from the commit message, massage. ]

Signed-off-by: default avatarBrijesh Singh <brijesh.singh@amd.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-44-brijesh.singh@amd.com
parent 3a45b375

Documentation/virt/coco/sevguest.rst

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.. SPDX-License-Identifier: GPL-2.0



===================================================================

The Definitive SEV Guest API Documentation

===================================================================



1. General description

======================



The SEV API is a set of ioctls that are used by the guest or hypervisor

to get or set a certain aspect of the SEV virtual machine. The ioctls belong

to the following classes:



 - Hypervisor ioctls: These query and set global attributes which affect the

   whole SEV firmware.  These ioctl are used by platform provisioning tools.



 - Guest ioctls: These query and set attributes of the SEV virtual machine.



2. API description

==================



This section describes ioctls that is used for querying the SEV guest report

from the SEV firmware. For each ioctl, the following information is provided

along with a description:



  Technology:

      which SEV technology provides this ioctl. SEV, SEV-ES, SEV-SNP or all.



  Type:

      hypervisor or guest. The ioctl can be used inside the guest or the

      hypervisor.



  Parameters:

      what parameters are accepted by the ioctl.



  Returns:

      the return value.  General error numbers (-ENOMEM, -EINVAL)

      are not detailed, but errors with specific meanings are.



The guest ioctl should be issued on a file descriptor of the /dev/sev-guest device.

The ioctl accepts struct snp_user_guest_request. The input and output structure is

specified through the req_data and resp_data field respectively. If the ioctl fails

to execute due to a firmware error, then fw_err code will be set otherwise the

fw_err will be set to 0x00000000000000ff.



The firmware checks that the message sequence counter is one greater than

the guests message sequence counter. If guest driver fails to increment message

counter (e.g. counter overflow), then -EIO will be returned.



::



        struct snp_guest_request_ioctl {

                /* Message version number */

                __u32 msg_version;



                /* Request and response structure address */

                __u64 req_data;

                __u64 resp_data;



                /* firmware error code on failure (see psp-sev.h) */

                __u64 fw_err;

        };



2.1 SNP_GET_REPORT

------------------



:Technology: sev-snp

:Type: guest ioctl

:Parameters (in): struct snp_report_req

:Returns (out): struct snp_report_resp on success, -negative on error



The SNP_GET_REPORT ioctl can be used to query the attestation report from the

SEV-SNP firmware. The ioctl uses the SNP_GUEST_REQUEST (MSG_REPORT_REQ) command

provided by the SEV-SNP firmware to query the attestation report.



On success, the snp_report_resp.data will contains the report. The report

contain the format described in the SEV-SNP specification. See the SEV-SNP

specification for further details.





Reference

---------



SEV-SNP and GHCB specification: developer.amd.com/sev



The driver is based on SEV-SNP firmware spec 0.9 and GHCB spec version 2.0.

Documentation/virt/index.rst

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@@ -13,6 +13,7 @@ Linux Virtualization Support 
   guest-halt-polling

   ne_overview

   acrn/index

   coco/sevguest



.. only:: html and subproject

drivers/virt/Kconfig

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@@ -47,4 +47,7 @@ source "drivers/virt/vboxguest/Kconfig" 
source "drivers/virt/nitro_enclaves/Kconfig"



source "drivers/virt/acrn/Kconfig"



source "drivers/virt/coco/sevguest/Kconfig"



endif

drivers/virt/Makefile

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@@ -9,3 +9,4 @@ obj-y += vboxguest/ 


obj-$(CONFIG_NITRO_ENCLAVES)	+= nitro_enclaves/

obj-$(CONFIG_ACRN_HSM)		+= acrn/

obj-$(CONFIG_SEV_GUEST)		+= coco/sevguest/

drivers/virt/coco/sevguest/Kconfig

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config SEV_GUEST

	tristate "AMD SEV Guest driver"

	default m

	depends on AMD_MEM_ENCRYPT

	select CRYPTO_AEAD2

	select CRYPTO_GCM

	help

	  SEV-SNP firmware provides the guest a mechanism to communicate with

	  the PSP without risk from a malicious hypervisor who wishes to read,

	  alter, drop or replay the messages sent. The driver provides

	  userspace interface to communicate with the PSP to request the

	  attestation report and more.



	  If you choose 'M' here, this module will be called sevguest.