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

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