diff options
Diffstat (limited to 'drivers/virt/coco/sevguest/sevguest.c')
| -rw-r--r-- | drivers/virt/coco/sevguest/sevguest.c | 607 |
1 files changed, 607 insertions, 0 deletions
diff --git a/drivers/virt/coco/sevguest/sevguest.c b/drivers/virt/coco/sevguest/sevguest.c new file mode 100644 index 000000000000..beda93cdeb4f --- /dev/null +++ b/drivers/virt/coco/sevguest/sevguest.c @@ -0,0 +1,607 @@ +// 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"); |