Re: [PATCH v7 43/45] virt: Add SEV-SNP guest driver

[Peter Gonda <pgonda@google.com>]

On Wed, Nov 10, 2021 at 3:09 PM Brijesh Singh <brijesh.singh@amd.com> wrote:
>
> SEV-SNP specification provides the guest a mechanisum to communicate with

mechanism

> 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 the platform_data.
>
> The userspace can use SNP_GET_REPORT ioctl() to query the guest
> attestation report.
>
> See SEV-SNP spec section Guest Messages for more details.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
>  Documentation/virt/coco/sevguest.rst  |  77 ++++
>  drivers/virt/Kconfig                  |   3 +
>  drivers/virt/Makefile                 |   1 +
>  drivers/virt/coco/sevguest/Kconfig    |   9 +
>  drivers/virt/coco/sevguest/Makefile   |   2 +
>  drivers/virt/coco/sevguest/sevguest.c | 601 ++++++++++++++++++++++++++
>  drivers/virt/coco/sevguest/sevguest.h |  98 +++++
>  include/uapi/linux/sev-guest.h        |  44 ++
>  8 files changed, 835 insertions(+)
>  create mode 100644 Documentation/virt/coco/sevguest.rst
>  create mode 100644 drivers/virt/coco/sevguest/Kconfig
>  create mode 100644 drivers/virt/coco/sevguest/Makefile
>  create mode 100644 drivers/virt/coco/sevguest/sevguest.c
>  create mode 100644 drivers/virt/coco/sevguest/sevguest.h
>  create mode 100644 include/uapi/linux/sev-guest.h
>
> diff --git a/Documentation/virt/coco/sevguest.rst b/Documentation/virt/coco/sevguest.rst
> new file mode 100644
> index 000000000000..002c90946b8a
> --- /dev/null
> +++ b/Documentation/virt/coco/sevguest.rst
> @@ -0,0 +1,77 @@
> +.. 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 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 provision tools.
> +
> + - Guest ioctls: These query and set attributes of the SEV virtual machine.
> +
> +2. API description
> +==================
> +
> +This section describes ioctls that can be used to query or set SEV guests.
> +For each ioctl, the following information is provided along with a
> +description:
> +
> +  Technology:
> +      which SEV techology provides this ioctl. sev, sev-es, sev-snp or all.

technology

> +
> +  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.

Should way say what it will be set to? Also Sean pointed out on CCP
driver that 0 is strange to set the error to, its a uint so we cannot
do -1 like we did there. What about all FFs?

> +
> +::
> +        struct snp_guest_request_ioctl {
> +                /* 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

> +will 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.
> diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
> index 8061e8ef449f..e457e47610d3 100644
> --- a/drivers/virt/Kconfig
> +++ b/drivers/virt/Kconfig
> @@ -36,4 +36,7 @@ source "drivers/virt/vboxguest/Kconfig"
>  source "drivers/virt/nitro_enclaves/Kconfig"
>
>  source "drivers/virt/acrn/Kconfig"
> +
> +source "drivers/virt/coco/sevguest/Kconfig"
> +
>  endif
> diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
> index 3e272ea60cd9..9c704a6fdcda 100644
> --- a/drivers/virt/Makefile
> +++ b/drivers/virt/Makefile
> @@ -8,3 +8,4 @@ obj-y                           += vboxguest/
>
>  obj-$(CONFIG_NITRO_ENCLAVES)   += nitro_enclaves/
>  obj-$(CONFIG_ACRN_HSM)         += acrn/
> +obj-$(CONFIG_SEV_GUEST)                += coco/sevguest/
> diff --git a/drivers/virt/coco/sevguest/Kconfig b/drivers/virt/coco/sevguest/Kconfig
> new file mode 100644
> index 000000000000..96190919cca8
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/Kconfig
> @@ -0,0 +1,9 @@
> +config SEV_GUEST
> +       tristate "AMD SEV Guest driver"
> +       default y
> +       depends on AMD_MEM_ENCRYPT && CRYPTO_AEAD2
> +       help
> +         The driver can be used by the SEV-SNP guest to communicate with the PSP to
> +         request the attestation report and more.
> +
> +         If you choose 'M' here, this module will be called sevguest.
> diff --git a/drivers/virt/coco/sevguest/Makefile b/drivers/virt/coco/sevguest/Makefile
> new file mode 100644
> index 000000000000..b1ffb2b4177b
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +obj-$(CONFIG_SEV_GUEST) += sevguest.o
> diff --git a/drivers/virt/coco/sevguest/sevguest.c b/drivers/virt/coco/sevguest/sevguest.c
> new file mode 100644
> index 000000000000..982714c1b4ca
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/sevguest.c
> @@ -0,0 +1,601 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * AMD Secure Encrypted Virtualization Nested Paging (SEV-SNP) guest request interface
> + *
> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
> + *
> + * Author: Brijesh Singh <brijesh.singh@amd.com>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/types.h>
> +#include <linux/mutex.h>
> +#include <linux/io.h>
> +#include <linux/platform_device.h>
> +#include <linux/miscdevice.h>
> +#include <linux/set_memory.h>
> +#include <linux/fs.h>
> +#include <crypto/aead.h>
> +#include <linux/scatterlist.h>
> +#include <linux/psp-sev.h>
> +#include <uapi/linux/sev-guest.h>
> +#include <uapi/linux/psp-sev.h>
> +
> +#include <asm/svm.h>
> +#include <asm/sev.h>
> +
> +#include "sevguest.h"
> +
> +#define DEVICE_NAME    "sev-guest"
> +#define AAD_LEN                48
> +#define MSG_HDR_VER    1
> +
> +struct snp_guest_crypto {
> +       struct crypto_aead *tfm;
> +       u8 *iv, *authtag;
> +       int iv_len, a_len;
> +};
> +
> +struct snp_guest_dev {
> +       struct device *dev;
> +       struct miscdevice misc;
> +
> +       struct snp_guest_crypto *crypto;
> +       struct snp_guest_msg *request, *response;
> +       struct snp_secrets_page_layout *layout;
> +       struct snp_req_data input;
> +       u32 *os_area_msg_seqno;
> +       u8 *vmpck;
> +};
> +
> +static u32 vmpck_id;
> +module_param(vmpck_id, uint, 0444);
> +MODULE_PARM_DESC(vmpck_id, "The VMPCK ID to use when communicating with the PSP.");
> +
> +static DEFINE_MUTEX(snp_cmd_mutex);
> +
> +static bool is_vmpck_empty(struct snp_guest_dev *snp_dev)
> +{
> +       char zero_key[VMPCK_KEY_LEN] = {0};
> +
> +       if (snp_dev->vmpck)
> +               return memcmp(snp_dev->vmpck, zero_key, VMPCK_KEY_LEN) == 0;
> +
> +       return true;
> +}
> +
> +static void snp_disable_vmpck(struct snp_guest_dev *snp_dev)
> +{
> +       memzero_explicit(snp_dev->vmpck, VMPCK_KEY_LEN);
> +       snp_dev->vmpck = NULL;
> +}
> +
> +static inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> +       u64 count;

I may be overly paranoid here but how about
`lockdep_assert_held(&snp_cmd_mutex);` when writing or reading
directly from this data?

> +
> +       /* Read the current message sequence counter from secrets pages */
> +       count = *snp_dev->os_area_msg_seqno;
> +
> +       return count + 1;
> +}
> +
> +/* Return a non-zero on success */
> +static u64 snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> +       u64 count = __snp_get_msg_seqno(snp_dev);
> +
> +       /*
> +        * The message sequence counter for the SNP guest request is a  64-bit
> +        * value but the version 2 of GHCB specification defines a 32-bit storage
> +        * for the it. If the counter exceeds the 32-bit value then return zero.

"for it. ..." or maybe "defines 32-bit field for the sequence counter"

> +        * The caller should check the return value, but if the caller happen to

happens

> +        * not check the value and use it, then the firmware treats zero as an
> +        * invalid number and will fail the  message request.
> +        */
> +       if (count >= UINT_MAX) {
> +               pr_err_ratelimited("SNP guest request message sequence counter overflow\n");
> +               return 0;
> +       }
> +
> +       return count;
> +}
> +
> +static void snp_inc_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> +       /*
> +        * The counter is also incremented by the PSP, so increment it by 2
> +        * and save in secrets page.
> +        */
> +       *snp_dev->os_area_msg_seqno += 2;
> +}
> +
> +static inline struct snp_guest_dev *to_snp_dev(struct file *file)
> +{
> +       struct miscdevice *dev = file->private_data;
> +
> +       return container_of(dev, struct snp_guest_dev, misc);
> +}
> +
> +static struct snp_guest_crypto *init_crypto(struct snp_guest_dev *snp_dev, u8 *key, size_t keylen)
> +{
> +       struct snp_guest_crypto *crypto;
> +
> +       crypto = kzalloc(sizeof(*crypto), GFP_KERNEL_ACCOUNT);
> +       if (!crypto)
> +               return NULL;
> +
> +       crypto->tfm = crypto_alloc_aead("gcm(aes)", 0, 0);
> +       if (IS_ERR(crypto->tfm))
> +               goto e_free;
> +
> +       if (crypto_aead_setkey(crypto->tfm, key, keylen))
> +               goto e_free_crypto;
> +
> +       crypto->iv_len = crypto_aead_ivsize(crypto->tfm);
> +       if (crypto->iv_len < 12) {
> +               dev_err(snp_dev->dev, "IV length is less than 12.\n");
> +               goto e_free_crypto;
> +       }
> +
> +       crypto->iv = kmalloc(crypto->iv_len, GFP_KERNEL_ACCOUNT);
> +       if (!crypto->iv)
> +               goto e_free_crypto;
> +
> +       if (crypto_aead_authsize(crypto->tfm) > MAX_AUTHTAG_LEN) {
> +               if (crypto_aead_setauthsize(crypto->tfm, MAX_AUTHTAG_LEN)) {
> +                       dev_err(snp_dev->dev, "failed to set authsize to %d\n", MAX_AUTHTAG_LEN);
> +                       goto e_free_crypto;
> +               }
> +       }
> +
> +       crypto->a_len = crypto_aead_authsize(crypto->tfm);
> +       crypto->authtag = kmalloc(crypto->a_len, GFP_KERNEL_ACCOUNT);
> +       if (!crypto->authtag)
> +               goto e_free_crypto;
> +
> +       return crypto;
> +
> +e_free_crypto:
> +       crypto_free_aead(crypto->tfm);
> +e_free:
> +       kfree(crypto->iv);
> +       kfree(crypto->authtag);
> +       kfree(crypto);
> +
> +       return NULL;
> +}
> +
> +static void deinit_crypto(struct snp_guest_crypto *crypto)
> +{
> +       crypto_free_aead(crypto->tfm);
> +       kfree(crypto->iv);
> +       kfree(crypto->authtag);
> +       kfree(crypto);
> +}
> +
> +static int enc_dec_message(struct snp_guest_crypto *crypto, struct snp_guest_msg *msg,
> +                          u8 *src_buf, u8 *dst_buf, size_t len, bool enc)
> +{
> +       struct snp_guest_msg_hdr *hdr = &msg->hdr;
> +       struct scatterlist src[3], dst[3];
> +       DECLARE_CRYPTO_WAIT(wait);
> +       struct aead_request *req;
> +       int ret;
> +
> +       req = aead_request_alloc(crypto->tfm, GFP_KERNEL);
> +       if (!req)
> +               return -ENOMEM;
> +
> +       /*
> +        * AEAD memory operations:
> +        * +------ AAD -------+------- DATA -----+---- AUTHTAG----+
> +        * |  msg header      |  plaintext       |  hdr->authtag  |
> +        * | bytes 30h - 5Fh  |    or            |                |
> +        * |                  |   cipher         |                |
> +        * +------------------+------------------+----------------+
> +        */
> +       sg_init_table(src, 3);
> +       sg_set_buf(&src[0], &hdr->algo, AAD_LEN);
> +       sg_set_buf(&src[1], src_buf, hdr->msg_sz);
> +       sg_set_buf(&src[2], hdr->authtag, crypto->a_len);
> +
> +       sg_init_table(dst, 3);
> +       sg_set_buf(&dst[0], &hdr->algo, AAD_LEN);
> +       sg_set_buf(&dst[1], dst_buf, hdr->msg_sz);
> +       sg_set_buf(&dst[2], hdr->authtag, crypto->a_len);
> +
> +       aead_request_set_ad(req, AAD_LEN);
> +       aead_request_set_tfm(req, crypto->tfm);
> +       aead_request_set_callback(req, 0, crypto_req_done, &wait);
> +
> +       aead_request_set_crypt(req, src, dst, len, crypto->iv);
> +       ret = crypto_wait_req(enc ? crypto_aead_encrypt(req) : crypto_aead_decrypt(req), &wait);
> +
> +       aead_request_free(req);
> +       return ret;
> +}
> +
> +static int __enc_payload(struct snp_guest_dev *snp_dev, struct snp_guest_msg *msg,
> +                        void *plaintext, size_t len)
> +{
> +       struct snp_guest_crypto *crypto = snp_dev->crypto;
> +       struct snp_guest_msg_hdr *hdr = &msg->hdr;
> +
> +       memset(crypto->iv, 0, crypto->iv_len);
> +       memcpy(crypto->iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> +
> +       return enc_dec_message(crypto, msg, plaintext, msg->payload, len, true);
> +}
> +
> +static int dec_payload(struct snp_guest_dev *snp_dev, struct snp_guest_msg *msg,
> +                      void *plaintext, size_t len)
> +{
> +       struct snp_guest_crypto *crypto = snp_dev->crypto;
> +       struct snp_guest_msg_hdr *hdr = &msg->hdr;
> +
> +       /* Build IV with response buffer sequence number */
> +       memset(crypto->iv, 0, crypto->iv_len);
> +       memcpy(crypto->iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> +
> +       return enc_dec_message(crypto, msg, msg->payload, plaintext, len, false);
> +}
> +
> +static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, void *payload, u32 sz)
> +{
> +       struct snp_guest_crypto *crypto = snp_dev->crypto;
> +       struct snp_guest_msg *resp = snp_dev->response;
> +       struct snp_guest_msg *req = snp_dev->request;
> +       struct snp_guest_msg_hdr *req_hdr = &req->hdr;
> +       struct snp_guest_msg_hdr *resp_hdr = &resp->hdr;
> +
> +       dev_dbg(snp_dev->dev, "response [seqno %lld type %d version %d sz %d]\n",
> +               resp_hdr->msg_seqno, resp_hdr->msg_type, resp_hdr->msg_version, resp_hdr->msg_sz);
> +
> +       /* Verify that the sequence counter is incremented by 1 */
> +       if (unlikely(resp_hdr->msg_seqno != (req_hdr->msg_seqno + 1)))
> +               return -EBADMSG;
> +
> +       /* Verify response message type and version number. */
> +       if (resp_hdr->msg_type != (req_hdr->msg_type + 1) ||
> +           resp_hdr->msg_version != req_hdr->msg_version)
> +               return -EBADMSG;
> +
> +       /*
> +        * If the message size is greater than our buffer length then return
> +        * an error.
> +        */
> +       if (unlikely((resp_hdr->msg_sz + crypto->a_len) > sz))
> +               return -EBADMSG;
> +
> +       /* Decrypt the payload */
> +       return dec_payload(snp_dev, resp, payload, resp_hdr->msg_sz + crypto->a_len);
> +}
> +
> +static bool enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8 type,
> +                       void *payload, size_t sz)
> +{
> +       struct snp_guest_msg *req = snp_dev->request;
> +       struct snp_guest_msg_hdr *hdr = &req->hdr;
> +
> +       memset(req, 0, sizeof(*req));
> +
> +       hdr->algo = SNP_AEAD_AES_256_GCM;
> +       hdr->hdr_version = MSG_HDR_VER;
> +       hdr->hdr_sz = sizeof(*hdr);
> +       hdr->msg_type = type;
> +       hdr->msg_version = version;
> +       hdr->msg_seqno = seqno;
> +       hdr->msg_vmpck = vmpck_id;
> +       hdr->msg_sz = sz;
> +
> +       /* Verify the sequence number is non-zero */
> +       if (!hdr->msg_seqno)
> +               return -ENOSR;
> +
> +       dev_dbg(snp_dev->dev, "request [seqno %lld type %d version %d sz %d]\n",
> +               hdr->msg_seqno, hdr->msg_type, hdr->msg_version, hdr->msg_sz);
> +
> +       return __enc_payload(snp_dev, req, payload, sz);
> +}
> +
> +static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, int msg_ver,
> +                               u8 type, void *req_buf, size_t req_sz, void *resp_buf,
> +                               u32 resp_sz, __u64 *fw_err)
> +{
> +       unsigned long err;
> +       u64 seqno;
> +       int rc;
> +
> +       /* Get message sequence and verify that its a non-zero */
> +       seqno = snp_get_msg_seqno(snp_dev);
> +       if (!seqno)
> +               return -EIO;
> +
> +       memset(snp_dev->response, 0, sizeof(*snp_dev->response));
> +
> +       /* Encrypt the userspace provided payload */
> +       rc = enc_payload(snp_dev, seqno, msg_ver, type, req_buf, req_sz);
> +       if (rc)
> +               return rc;
> +
> +       /* Call firmware to process the request */
> +       rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);

Isn't everything in the file going to be calling this with
SVM_VMGEXIT_EXT_GUEST_REQUEST because they are all placing guest
requests? If so, why not drop the @exit_code parameter and just
hardcode SVM_VMGEXIT_EXT_GUEST_REQUEST here?

> +       if (fw_err)
> +               *fw_err = err;
> +
> +       if (rc)
> +               return rc;
> +
> +       rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
> +       if (rc) {
> +               /*
> +                * The verify_and_dec_payload() will fail only if the hypervisor is
> +                * actively modifiying the message header or corrupting the encrypted payload.
modifiying
> +                * This hints that hypervisor is acting in a bad faith. Disable the VMPCK so that
> +                * the key cannot be used for any communication.
> +                */

This looks great, thanks for changes Brijesh. Should we mention in
comment here or at snp_disable_vmpck() the AES-GCM issues with
continuing to use the key? Or will future updaters to this code
understand already?


> +               dev_alert(snp_dev->dev,
> +                         "Detected unexpected decode failure, disabling the vmpck_id %d\n", vmpck_id);
> +               snp_disable_vmpck(snp_dev);
> +               return rc;
> +       }
> +
> +       /* Increment to new message sequence after payload descryption was successful. */
> +       snp_inc_msg_seqno(snp_dev);
> +
> +       return 0;
> +}
> +
> +static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
> +{
> +       struct snp_guest_crypto *crypto = snp_dev->crypto;
> +       struct snp_report_resp *resp;
> +       struct snp_report_req req;
> +       int rc, resp_len;
> +
> +       if (!arg->req_data || !arg->resp_data)
> +               return -EINVAL;
> +
> +       /* Copy the request payload from userspace */
> +       if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
> +               return -EFAULT;
> +
> +       /* Message version must be non-zero */
> +       if (!req.msg_version)
> +               return -EINVAL;
> +
> +       /*
> +        * The intermediate response buffer is used while decrypting the
> +        * response payload. Make sure that it has enough space to cover the
> +        * authtag.
> +        */
> +       resp_len = sizeof(resp->data) + crypto->a_len;
> +       resp = kzalloc(resp_len, GFP_KERNEL_ACCOUNT);
> +       if (!resp)
> +               return -ENOMEM;
> +
> +       /* Issue the command to get the attestation report */
> +       rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, req.msg_version,
> +                                 SNP_MSG_REPORT_REQ, &req.user_data, sizeof(req.user_data),
> +                                 resp->data, resp_len, &arg->fw_err);
> +       if (rc)
> +               goto e_free;
> +
> +       /* Copy the response payload to userspace */
> +       if (copy_to_user((void __user *)arg->resp_data, resp, sizeof(*resp)))
> +               rc = -EFAULT;
> +
> +e_free:
> +       kfree(resp);
> +       return rc;
> +}
> +
> +static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
> +{
> +       struct snp_guest_dev *snp_dev = to_snp_dev(file);
> +       void __user *argp = (void __user *)arg;
> +       struct snp_guest_request_ioctl input;
> +       int ret = -ENOTTY;
> +
> +       if (copy_from_user(&input, argp, sizeof(input)))
> +               return -EFAULT;
> +
> +       input.fw_err = 0;
> +
> +       mutex_lock(&snp_cmd_mutex);
> +
> +       /* Check if the VMPCK is not empty */
> +       if (is_vmpck_empty(snp_dev)) {
> +               dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
> +               mutex_unlock(&snp_cmd_mutex);
> +               return -ENOTTY;
> +       }
> +
> +       switch (ioctl) {
> +       case SNP_GET_REPORT:
> +               ret = get_report(snp_dev, &input);
> +               break;
> +       default:
> +               break;
> +       }
> +
> +       mutex_unlock(&snp_cmd_mutex);
> +
> +       if (input.fw_err && copy_to_user(argp, &input, sizeof(input)))
> +               return -EFAULT;
> +
> +       return ret;
> +}
> +
> +static void free_shared_pages(void *buf, size_t sz)
> +{
> +       unsigned int npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
> +
> +       if (!buf)
> +               return;
> +
> +       /* If fail to restore the encryption mask then leak it. */
> +       if (WARN_ONCE(set_memory_encrypted((unsigned long)buf, npages),
> +                     "Failed to restore encryption mask (leak it)\n"))
> +               return;
> +
> +       __free_pages(virt_to_page(buf), get_order(sz));
> +}
> +
> +static void *alloc_shared_pages(size_t sz)
> +{
> +       unsigned int npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
> +       struct page *page;
> +       int ret;
> +
> +       page = alloc_pages(GFP_KERNEL_ACCOUNT, get_order(sz));
> +       if (IS_ERR(page))
> +               return NULL;
> +
> +       ret = set_memory_decrypted((unsigned long)page_address(page), npages);
> +       if (ret) {
> +               pr_err("SEV-SNP: failed to mark page shared, ret=%d\n", ret);
> +               __free_pages(page, get_order(sz));
> +               return NULL;
> +       }

No strong preference or anything just curious. Why not allocate from
SWIOTLB or use the DMA pool that supports decrypted memory:
https://lkml.org/lkml/2020/4/14/1508.


> +
> +       return page_address(page);
> +}
> +
> +static const struct file_operations snp_guest_fops = {
> +       .owner  = THIS_MODULE,
> +       .unlocked_ioctl = snp_guest_ioctl,
> +};
> +
> +static u8 *get_vmpck(int id, struct snp_secrets_page_layout *layout, u32 **seqno)
> +{
> +       u8 *key = NULL;
> +
> +       switch (id) {
> +       case 0:
> +               *seqno = &layout->os_area.msg_seqno_0;
> +               key = layout->vmpck0;
> +               break;
> +       case 1:
> +               *seqno = &layout->os_area.msg_seqno_1;
> +               key = layout->vmpck1;
> +               break;
> +       case 2:
> +               *seqno = &layout->os_area.msg_seqno_2;
> +               key = layout->vmpck2;
> +               break;
> +       case 3:
> +               *seqno = &layout->os_area.msg_seqno_3;
> +               key = layout->vmpck3;
> +               break;
> +       default:
> +               break;
> +       }
> +
> +       return key;
> +}
> +
> +static int __init snp_guest_probe(struct platform_device *pdev)
> +{
> +       struct snp_secrets_page_layout *layout;
> +       struct snp_guest_platform_data *data;
> +       struct device *dev = &pdev->dev;
> +       struct snp_guest_dev *snp_dev;
> +       struct miscdevice *misc;
> +       int ret;
> +
> +       if (!dev->platform_data)
> +               return -ENODEV;
> +
> +       data = (struct snp_guest_platform_data *)dev->platform_data;
> +       layout = (__force void *)ioremap_encrypted(data->secrets_gpa, PAGE_SIZE);
> +       if (!layout)
> +               return -ENODEV;
> +
> +       ret = -ENOMEM;
> +       snp_dev = devm_kzalloc(&pdev->dev, sizeof(struct snp_guest_dev), GFP_KERNEL);
> +       if (!snp_dev)
> +               goto e_fail;
> +
> +       ret = -EINVAL;
> +       snp_dev->vmpck = get_vmpck(vmpck_id, layout, &snp_dev->os_area_msg_seqno);
> +       if (!snp_dev->vmpck) {
> +               dev_err(dev, "invalid vmpck id %d\n", vmpck_id);
> +               goto e_fail;
> +       }
> +
> +       /* Verify that VMPCK is not zero. */
> +       if (is_vmpck_empty(snp_dev)) {
> +               dev_err(dev, "vmpck id %d is null\n", vmpck_id);
> +               goto e_fail;
> +       }
> +
> +       platform_set_drvdata(pdev, snp_dev);
> +       snp_dev->dev = dev;
> +       snp_dev->layout = layout;
> +
> +       /* Allocate the shared page used for the request and response message. */
> +       snp_dev->request = alloc_shared_pages(sizeof(struct snp_guest_msg));
> +       if (!snp_dev->request)
> +               goto e_fail;
> +
> +       snp_dev->response = alloc_shared_pages(sizeof(struct snp_guest_msg));
> +       if (!snp_dev->response)
> +               goto e_fail;
> +
> +       ret = -EIO;
> +       snp_dev->crypto = init_crypto(snp_dev, snp_dev->vmpck, VMPCK_KEY_LEN);
> +       if (!snp_dev->crypto)
> +               goto e_fail;
> +
> +       misc = &snp_dev->misc;
> +       misc->minor = MISC_DYNAMIC_MINOR;
> +       misc->name = DEVICE_NAME;
> +       misc->fops = &snp_guest_fops;
> +
> +       /* initial the input address for guest request */
> +       snp_dev->input.req_gpa = __pa(snp_dev->request);
> +       snp_dev->input.resp_gpa = __pa(snp_dev->response);
> +
> +       ret =  misc_register(misc);
> +       if (ret)
> +               goto e_fail;
> +
> +       dev_info(dev, "Initialized SNP guest driver (using vmpck_id %d)\n", vmpck_id);
> +       return 0;
> +
> +e_fail:
> +       iounmap(layout);
> +       free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
> +       free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
> +
> +       return ret;
> +}
> +
> +static int __exit snp_guest_remove(struct platform_device *pdev)
> +{
> +       struct snp_guest_dev *snp_dev = platform_get_drvdata(pdev);
> +
> +       free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
> +       free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
> +       deinit_crypto(snp_dev->crypto);
> +       misc_deregister(&snp_dev->misc);
> +
> +       return 0;
> +}
> +
> +static struct platform_driver snp_guest_driver = {
> +       .remove         = __exit_p(snp_guest_remove),
> +       .driver         = {
> +               .name = "snp-guest",
> +       },
> +};
> +
> +module_platform_driver_probe(snp_guest_driver, snp_guest_probe);
> +
> +MODULE_AUTHOR("Brijesh Singh <brijesh.singh@amd.com>");
> +MODULE_LICENSE("GPL");
> +MODULE_VERSION("1.0.0");
> +MODULE_DESCRIPTION("AMD SNP Guest Driver");
> diff --git a/drivers/virt/coco/sevguest/sevguest.h b/drivers/virt/coco/sevguest/sevguest.h
> new file mode 100644
> index 000000000000..cfa76cf8a21a
> --- /dev/null
> +++ b/drivers/virt/coco/sevguest/sevguest.h
> @@ -0,0 +1,98 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
> + *
> + * Author: Brijesh Singh <brijesh.singh@amd.com>
> + *
> + * SEV-SNP API spec is available at https://developer.amd.com/sev
> + */
> +
> +#ifndef __LINUX_SEVGUEST_H_
> +#define __LINUX_SEVGUEST_H_
> +
> +#include <linux/types.h>
> +
> +#define MAX_AUTHTAG_LEN                32
> +
> +/* See SNP spec SNP_GUEST_REQUEST section for the structure */
> +enum msg_type {
> +       SNP_MSG_TYPE_INVALID = 0,
> +       SNP_MSG_CPUID_REQ,
> +       SNP_MSG_CPUID_RSP,
> +       SNP_MSG_KEY_REQ,
> +       SNP_MSG_KEY_RSP,
> +       SNP_MSG_REPORT_REQ,
> +       SNP_MSG_REPORT_RSP,
> +       SNP_MSG_EXPORT_REQ,
> +       SNP_MSG_EXPORT_RSP,
> +       SNP_MSG_IMPORT_REQ,
> +       SNP_MSG_IMPORT_RSP,
> +       SNP_MSG_ABSORB_REQ,
> +       SNP_MSG_ABSORB_RSP,
> +       SNP_MSG_VMRK_REQ,
> +       SNP_MSG_VMRK_RSP,

Did you want to include MSG_ABSORB_NOMA_REQ and MSG_ABSORB_NOMA_RESP here?


> +
> +       SNP_MSG_TYPE_MAX
> +};
> +
> +enum aead_algo {
> +       SNP_AEAD_INVALID,
> +       SNP_AEAD_AES_256_GCM,
> +};
> +
> +struct snp_guest_msg_hdr {
> +       u8 authtag[MAX_AUTHTAG_LEN];
> +       u64 msg_seqno;
> +       u8 rsvd1[8];
> +       u8 algo;
> +       u8 hdr_version;
> +       u16 hdr_sz;
> +       u8 msg_type;
> +       u8 msg_version;
> +       u16 msg_sz;
> +       u32 rsvd2;
> +       u8 msg_vmpck;
> +       u8 rsvd3[35];
> +} __packed;
> +
> +struct snp_guest_msg {
> +       struct snp_guest_msg_hdr hdr;
> +       u8 payload[4000];
> +} __packed;
> +
> +/*
> + * The secrets page contains 96-bytes of reserved field that can be used by
> + * the guest OS. The guest OS uses the area to save the message sequence
> + * number for each VMPCK.
> + *
> + * See the GHCB spec section Secret page layout for the format for this area.
> + */
> +struct secrets_os_area {
> +       u32 msg_seqno_0;
> +       u32 msg_seqno_1;
> +       u32 msg_seqno_2;
> +       u32 msg_seqno_3;
> +       u64 ap_jump_table_pa;
> +       u8 rsvd[40];
> +       u8 guest_usage[32];
> +} __packed;
> +
> +#define VMPCK_KEY_LEN          32
> +
> +/* See the SNP spec version 0.9 for secrets page format */
> +struct snp_secrets_page_layout {
> +       u32 version;
> +       u32 imien       : 1,
> +           rsvd1       : 31;
> +       u32 fms;
> +       u32 rsvd2;
> +       u8 gosvw[16];
> +       u8 vmpck0[VMPCK_KEY_LEN];
> +       u8 vmpck1[VMPCK_KEY_LEN];
> +       u8 vmpck2[VMPCK_KEY_LEN];
> +       u8 vmpck3[VMPCK_KEY_LEN];
> +       struct secrets_os_area os_area;
> +       u8 rsvd3[3840];
> +} __packed;
> +
> +#endif /* __LINUX_SNP_GUEST_H__ */
> diff --git a/include/uapi/linux/sev-guest.h b/include/uapi/linux/sev-guest.h
> new file mode 100644
> index 000000000000..eda7edcffda8
> --- /dev/null
> +++ b/include/uapi/linux/sev-guest.h
> @@ -0,0 +1,44 @@
> +/* SPDX-License-Identifier: GPL-2.0-only WITH Linux-syscall-note */
> +/*
> + * Userspace interface for AMD SEV and SEV-SNP guest driver.
> + *
> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
> + *
> + * Author: Brijesh Singh <brijesh.singh@amd.com>
> + *
> + * SEV API specification is available at: https://developer.amd.com/sev/
> + */
> +
> +#ifndef __UAPI_LINUX_SEV_GUEST_H_
> +#define __UAPI_LINUX_SEV_GUEST_H_
> +
> +#include <linux/types.h>
> +
> +struct snp_report_req {
> +       /* message version number (must be non-zero) */
> +       __u8 msg_version;
> +
> +       /* user data that should be included in the report */
> +       __u8 user_data[64];

Are we missing the 'vmpl' field here? Does those default all requests
to be signed with VMPL0? Users might want to change that, they could
be using a paravisor.

> +};
> +
> +struct snp_report_resp {
> +       /* response data, see SEV-SNP spec for the format */
> +       __u8 data[4000];
> +};
> +
> +struct snp_guest_request_ioctl {
> +       /* Request and response structure address */
> +       __u64 req_data;
> +       __u64 resp_data;
> +
> +       /* firmware error code on failure (see psp-sev.h) */
> +       __u64 fw_err;
> +};
> +
> +#define SNP_GUEST_REQ_IOC_TYPE 'S'
> +
> +/* Get SNP attestation report */
> +#define SNP_GET_REPORT _IOWR(SNP_GUEST_REQ_IOC_TYPE, 0x0, struct snp_guest_request_ioctl)
> +
> +#endif /* __UAPI_LINUX_SEV_GUEST_H_ */
> --
> 2.25.1
>