--- /dev/null
+// 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>
+ */
+
+#define pr_fmt(fmt) "SNP: GUEST: " fmt
+
+#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.");
+
+/* Mutex to serialize the shared buffer access and command handling. */
+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);
+
+ 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;
+
+ lockdep_assert_held(&snp_cmd_mutex);
+
+ /* 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 it. If the counter exceeds the 32-bit value then return zero.
+ * The caller should check the return value, but if the caller happens to
+ * 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) {
+ dev_err(snp_dev->dev, "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);
+ 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_iv;
+ }
+ }
+
+ crypto->a_len = crypto_aead_authsize(crypto->tfm);
+ crypto->authtag = kmalloc(crypto->a_len, GFP_KERNEL_ACCOUNT);
+ if (!crypto->authtag)
+ goto e_free_auth;
+
+ return crypto;
+
+e_free_auth:
+ kfree(crypto->authtag);
+e_free_iv:
+ kfree(crypto->iv);
+e_free_crypto:
+ crypto_free_aead(crypto->tfm);
+e_free:
+ 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(struct snp_guest_msg));
+
+ /* 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);
+ if (fw_err)
+ *fw_err = err;
+
+ if (rc)
+ return rc;
+
+ /*
+ * The verify_and_dec_payload() will fail only if the hypervisor is
+ * actively modifying the message header or corrupting the encrypted payload.
+ * This hints that hypervisor is acting in a bad faith. Disable the VMPCK so that
+ * the key cannot be used for any communication. The key is disabled to ensure
+ * that AES-GCM does not use the same IV while encrypting the request payload.
+ */
+ rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
+ if (rc) {
+ 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 decryption 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;
+
+ lockdep_assert_held(&snp_cmd_mutex);
+
+ if (!arg->req_data || !arg->resp_data)
+ return -EINVAL;
+
+ if (copy_from_user(&req, (void __user *)arg->req_data, sizeof(req)))
+ return -EFAULT;
+
+ /*
+ * 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;
+
+ rc = handle_guest_request(snp_dev, SVM_VMGEXIT_GUEST_REQUEST, arg->msg_version,
+ SNP_MSG_REPORT_REQ, &req, sizeof(req), resp->data,
+ resp_len, &arg->fw_err);
+ if (rc)
+ goto e_free;
+
+ 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 = 0xff;
+
+ /* Message version must be non-zero */
+ if (!input.msg_version)
+ return -EINVAL;
+
+ 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;
+ int ret;
+
+ if (!buf)
+ return;
+
+ ret = set_memory_encrypted((unsigned long)buf, npages);
+ if (ret) {
+ WARN_ONCE(ret, "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("failed to mark page shared, ret=%d\n", ret);
+ __free_pages(page, get_order(sz));
+ return NULL;
+ }
+
+ 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_unmap;
+
+ 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_unmap;
+ }
+
+ /* 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_unmap;
+ }
+
+ 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_unmap;
+
+ snp_dev->response = alloc_shared_pages(sizeof(struct snp_guest_msg));
+ if (!snp_dev->response)
+ goto e_free_request;
+
+ ret = -EIO;
+ snp_dev->crypto = init_crypto(snp_dev, snp_dev->vmpck, VMPCK_KEY_LEN);
+ if (!snp_dev->crypto)
+ goto e_free_response;
+
+ 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_free_response;
+
+ dev_info(dev, "Initialized SNP guest driver (using vmpck_id %d)\n", vmpck_id);
+ return 0;
+
+e_free_response:
+ free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
+e_free_request:
+ free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
+e_unmap:
+ iounmap(layout);
+ 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->response, sizeof(struct snp_guest_msg));
+ free_shared_pages(snp_dev->request, 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");
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