SEV-SNP specification provides the guest a mechanisum to communicate with
the PSP without risk from a malicious hypervisor who wishes to read, alter,
drop or replay the messages sent. The driver uses snp_issue_guest_request()
to issue GHCB SNP_GUEST_REQUEST or SNP_EXT_GUEST_REQUEST NAE events to
submit the request to PSP.
The PSP requires that all communication should be encrypted using key
specified through 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@xxxxxxx>
---
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 | 561 ++++++++++++++++++++++++++
drivers/virt/coco/sevguest/sevguest.h | 98 +++++
include/uapi/linux/sev-guest.h | 44 ++
8 files changed, 795 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.
+
+ 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.
+
+::
+ 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
+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..2d313fb2ffae
--- /dev/null
+++ b/drivers/virt/coco/sevguest/sevguest.c
@@ -0,0 +1,561 @@
+// 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@xxxxxxx>
+ */
+
+#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;
+};
+
+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 inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
+{
+ u64 count;
+
+ /* 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.
+ * The caller should check the return value, but if the caller happen 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) {
+ 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;
+
+ 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);
+ if (fw_err)
+ *fw_err = err;
+
+ if (rc)
+ return rc;
+
+ rc = verify_and_dec_payload(snp_dev, resp_buf, resp_sz);
+ if (rc)
+ return rc;
+
+ /* Increment to new message sequence after the command is successful. */
+ snp_inc_msg_seqno(snp_dev);
