Re: [PATCH v6 07/16] x86/sev: Move and reorganize sev guest request api

Dionna Amalie Glaze
2023-12-05T17:13:55Z

On Tue, Nov 28, 2023 at 5:01 AM Nikunj A Dadhania <nikunj@amd.com> wrote:
>
> For enabling Secure TSC, SEV-SNP guests need to communicate with the
> AMD Security Processor early during boot. Many of the required
> functions are implemented in the sev-guest driver and therefore not
> available at early boot. Move the required functions and provide
> API to the sev guest driver for sending guest message and vmpck
> routines.
>
> As there is no external caller for snp_issue_guest_request() anymore,
> make it static and drop the prototype from sev-guest.h.
>
> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
> ---
> arch/x86/Kconfig | 1 +
> arch/x86/include/asm/sev-guest.h | 91 ++++-
> arch/x86/include/asm/sev.h | 10 -
> arch/x86/kernel/sev.c | 451 +++++++++++++++++++++-
> drivers/virt/coco/sev-guest/Kconfig | 1 -
> drivers/virt/coco/sev-guest/sev-guest.c | 479 +-----------------------
> 6 files changed, 550 insertions(+), 483 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 3762f41bb092..b8f374ec5651 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1534,6 +1534,7 @@ config AMD_MEM_ENCRYPT
> select ARCH_HAS_CC_PLATFORM
> select X86_MEM_ENCRYPT
> select UNACCEPTED_MEMORY
> + select CRYPTO_LIB_AESGCM
> help
> Say yes to enable support for the encryption of system memory.
> This requires an AMD processor that supports Secure Memory
> diff --git a/arch/x86/include/asm/sev-guest.h b/arch/x86/include/asm/sev-guest.h
> index 27cc15ad6131..16bf25c14e6f 100644
> --- a/arch/x86/include/asm/sev-guest.h
> +++ b/arch/x86/include/asm/sev-guest.h
> @@ -11,6 +11,11 @@
> #define __VIRT_SEVGUEST_H__
>
> #include <linux/types.h>
> +#include <linux/miscdevice.h>
> +#include <asm/sev.h>
> +
> +#define SNP_REQ_MAX_RETRY_DURATION (60*HZ)
> +#define SNP_REQ_RETRY_DELAY (2*HZ)
>
> #define MAX_AUTHTAG_LEN 32
> #define AUTHTAG_LEN 16
> @@ -58,11 +63,52 @@ struct snp_guest_msg_hdr {
> u8 rsvd3[35];
> } __packed;
>
> +/* SNP Guest message request */
> +struct snp_req_data {
> + unsigned long req_gpa;
> + unsigned long resp_gpa;
> +};
> +
> struct snp_guest_msg {
> struct snp_guest_msg_hdr hdr;
> u8 payload[4000];
> } __packed;
>
> +struct sev_guest_platform_data {
> + /* request and response are in unencrypted memory */
> + struct snp_guest_msg *request;
> + struct snp_guest_msg *response;
> +
> + struct snp_secrets_page_layout *layout;
> + struct snp_req_data input;
> +};
> +
> +struct snp_guest_dev {
> + struct device *dev;
> + struct miscdevice misc;
> +
> + /* Mutex to serialize the shared buffer access and command handling. */
> + struct mutex cmd_mutex;
> +
> + void *certs_data;
> + struct aesgcm_ctx *ctx;
> +
> + /*
> + * Avoid information leakage by double-buffering shared messages
> + * in fields that are in regular encrypted memory
> + */
> + struct snp_guest_msg secret_request;
> + struct snp_guest_msg secret_response;
> +
> + struct sev_guest_platform_data *pdata;
> + union {
> + struct snp_report_req report;
> + struct snp_derived_key_req derived_key;
> + struct snp_ext_report_req ext_report;
> + } req;
> + unsigned int vmpck_id;
> +};
> +
> struct snp_guest_req {
> void *req_buf;
> size_t req_sz;
> @@ -79,6 +125,47 @@ struct snp_guest_req {
> u8 msg_type;
> };
>
> -int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_data *input,
> - struct snp_guest_request_ioctl *rio);
> +int snp_setup_psp_messaging(struct snp_guest_dev *snp_dev);
> +int snp_send_guest_request(struct snp_guest_dev *dev, struct snp_guest_req *req,
> + struct snp_guest_request_ioctl *rio);
> +bool snp_assign_vmpck(struct snp_guest_dev *dev, unsigned int vmpck_id);
> +bool snp_is_vmpck_empty(unsigned int vmpck_id);
> +
> +static inline 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 inline 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 (!page)
> + return NULL;
> +
> + ret = set_memory_decrypted((unsigned long)page_address(page), npages);
> + if (ret) {
> + pr_err("%s: failed to mark page shared, ret=%d\n", __func__, ret);
> + __free_pages(page, get_order(sz));
> + return NULL;
> + }
> +
> + return page_address(page);
> +}
> +
> #endif /* __VIRT_SEVGUEST_H__ */
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 78465a8c7dc6..783150458864 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -93,16 +93,6 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
>
> #define RMPADJUST_VMSA_PAGE_BIT BIT(16)
>
> -/* SNP Guest message request */
> -struct snp_req_data {
> - unsigned long req_gpa;
> - unsigned long resp_gpa;
> -};
> -
> -struct sev_guest_platform_data {
> - u64 secrets_gpa;
> -};
> -
> /*
> * 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
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 479ea61f40f3..a413add2fd2c 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -24,6 +24,7 @@
> #include <linux/io.h>
> #include <linux/psp-sev.h>
> #include <uapi/linux/sev-guest.h>
> +#include <crypto/gcm.h>
>
> #include <asm/cpu_entry_area.h>
> #include <asm/stacktrace.h>
> @@ -2150,8 +2151,8 @@ static int __init init_sev_config(char *str)
> }
> __setup("sev=", init_sev_config);
>
> -int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_data *input,
> - struct snp_guest_request_ioctl *rio)
> +static int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_data *input,
> + struct snp_guest_request_ioctl *rio)
> {
> struct ghcb_state state;
> struct es_em_ctxt ctxt;
> @@ -2218,7 +2219,6 @@ int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_data *inpu
>
> return ret;
> }
> -EXPORT_SYMBOL_GPL(snp_issue_guest_request);
>
> static struct platform_device sev_guest_device = {
> .name = "sev-guest",
> @@ -2227,22 +2227,451 @@ static struct platform_device sev_guest_device = {
>
> static int __init snp_init_platform_device(void)
> {
> - struct sev_guest_platform_data data;
> -
> if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> return -ENODEV;
>
> - if (!secrets_pa)
> + if (platform_device_register(&sev_guest_device))
> return -ENODEV;
>
> - data.secrets_gpa = secrets_pa;
> - if (platform_device_add_data(&sev_guest_device, &data, sizeof(data)))
> + pr_info("SNP guest platform device initialized.\n");
> + return 0;
> +}
> +device_initcall(snp_init_platform_device);
> +
> +static struct sev_guest_platform_data *platform_data;
> +
> +static inline u8 *snp_get_vmpck(unsigned int vmpck_id)
> +{
> + if (!platform_data)
> + return NULL;
> +
> + return platform_data->layout->vmpck0 + vmpck_id * VMPCK_KEY_LEN;
> +}
> +
> +static inline u32 *snp_get_os_area_msg_seqno(unsigned int vmpck_id)
> +{
> + if (!platform_data)
> + return NULL;
> +
> + return &platform_data->layout->os_area.msg_seqno_0 + vmpck_id;
> +}
> +
> +bool snp_is_vmpck_empty(unsigned int vmpck_id)
> +{
> + char zero_key[VMPCK_KEY_LEN] = {0};
> + u8 *key = snp_get_vmpck(vmpck_id);
> +
> + if (key)
> + return !memcmp(key, zero_key, VMPCK_KEY_LEN);
> +
> + return true;
> +}
> +EXPORT_SYMBOL_GPL(snp_is_vmpck_empty);
> +
> +/*
> + * If an error is received from the host or AMD Secure Processor (ASP) there
> + * are two options. Either retry the exact same encrypted request or discontinue
> + * using the VMPCK.
> + *
> + * This is because in the current encryption scheme GHCB v2 uses AES-GCM to
> + * encrypt the requests. The IV for this scheme is the sequence number. GCM
> + * cannot tolerate IV reuse.
> + *
> + * The ASP FW v1.51 only increments the sequence numbers on a successful
> + * guest<->ASP back and forth and only accepts messages at its exact sequence
> + * number.
> + *
> + * So if the sequence number were to be reused the encryption scheme is
> + * vulnerable. If the sequence number were incremented for a fresh IV the ASP
> + * will reject the request.
> + */
> +static void snp_disable_vmpck(struct snp_guest_dev *snp_dev)
> +{
> + u8 *key = snp_get_vmpck(snp_dev->vmpck_id);
> +
> + pr_alert("Disabling vmpck_id %u to prevent IV reuse.\n", snp_dev->vmpck_id);
> + memzero_explicit(key, VMPCK_KEY_LEN);
> +}
> +
> +static inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> + u32 *os_area_msg_seqno = snp_get_os_area_msg_seqno(snp_dev->vmpck_id);
> + u64 count;
> +
> + if (!os_area_msg_seqno) {
> + pr_err("SNP unable to get message sequence counter\n");
> + return 0;
> + }
> +
> + lockdep_assert_held(&snp_dev->cmd_mutex);
> +
> + /* Read the current message sequence counter from secrets pages */
> + count = *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) {
> + pr_err("SNP request message sequence counter overflow\n");
> + return 0;
> + }
> +
> + return count;
> +}
> +
> +static void snp_inc_msg_seqno(struct snp_guest_dev *snp_dev)
> +{
> + u32 *os_area_msg_seqno = snp_get_os_area_msg_seqno(snp_dev->vmpck_id);
> +
> + if (!os_area_msg_seqno) {
> + pr_err("SNP unable to get message sequence counter\n");
> + return;
> + }
> +
> + lockdep_assert_held(&snp_dev->cmd_mutex);
> +
> + /*
> + * The counter is also incremented by the PSP, so increment it by 2
> + * and save in secrets page.
> + */
> + *os_area_msg_seqno += 2;
> +}
> +
> +static struct aesgcm_ctx *snp_init_crypto(unsigned int vmpck_id)
> +{
> + struct aesgcm_ctx *ctx;
> + u8 *key;
> +
> + if (snp_is_vmpck_empty(vmpck_id)) {
> + pr_err("VM communication key VMPCK%u is null\n", vmpck_id);
> + return NULL;
> + }
> +
> + ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
> + if (!ctx)
> + return NULL;
> +
> + key = snp_get_vmpck(vmpck_id);
> + if (aesgcm_expandkey(ctx, key, VMPCK_KEY_LEN, AUTHTAG_LEN)) {
> + pr_err("Crypto context initialization failed\n");
> + kfree(ctx);
> + return NULL;
> + }
> +
> + return ctx;
> +}
> +
> +int snp_setup_psp_messaging(struct snp_guest_dev *snp_dev)
> +{
> + struct sev_guest_platform_data *pdata;
> + int ret;
> +
> + if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP)) {

Note that this may be going away in favor of an
cpu_feature_enabled(X86_FEATURE_...) check given Kirill's "[PATCH]
x86/coco, x86/sev: Use cpu_feature_enabled() to detect SEV guest
flavor"

> + pr_err("SNP not supported\n");
> + return 0;
> + }
> +
> + if (platform_data) {
> + pr_debug("SNP platform data already initialized.\n");
> + goto create_ctx;
> + }
> +
> + if (!secrets_pa) {
> + pr_err("SNP secrets page not found\n");
> return -ENODEV;
> + }
>
> - if (platform_device_register(&sev_guest_device))
> + pdata = kzalloc(sizeof(struct sev_guest_platform_data), GFP_KERNEL);
> + if (!pdata) {
> + pr_err("Allocation of SNP guest platform data failed\n");
> + return -ENOMEM;
> + }
> +
> + pdata->layout = (__force void *)ioremap_encrypted(secrets_pa, PAGE_SIZE);
> + if (!pdata->layout) {
> + pr_err("Failed to map SNP secrets page.\n");
> + goto e_free_pdata;
> + }
> +
> + ret = -ENOMEM;
> + /* Allocate the shared page used for the request and response message. */
> + pdata->request = alloc_shared_pages(sizeof(struct snp_guest_msg));
> + if (!pdata->request)
> + goto e_unmap;
> +
> + pdata->response = alloc_shared_pages(sizeof(struct snp_guest_msg));
> + if (!pdata->response)
> + goto e_free_request;
> +
> + /* initial the input address for guest request */
> + pdata->input.req_gpa = __pa(pdata->request);
> + pdata->input.resp_gpa = __pa(pdata->response);
> + platform_data = pdata;
> +
> +create_ctx:
> + ret = -EIO;
> + snp_dev->ctx = snp_init_crypto(snp_dev->vmpck_id);
> + if (!snp_dev->ctx) {
> + pr_err("SNP crypto context initialization failed\n");
> + platform_data = NULL;
> + goto e_free_response;
> + }
> +
> + snp_dev->pdata = platform_data;
> +
> + return 0;
> +
> +e_free_response:
> + free_shared_pages(pdata->response, sizeof(struct snp_guest_msg));
> +e_free_request:
> + free_shared_pages(pdata->request, sizeof(struct snp_guest_msg));
> +e_unmap:
> + iounmap(pdata->layout);
> +e_free_pdata:
> + kfree(pdata);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(snp_setup_psp_messaging);
> +
> +static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, struct snp_guest_req *guest_req,
> + struct sev_guest_platform_data *pdata)
> +{
> + struct snp_guest_msg *resp = &snp_dev->secret_response;
> + struct snp_guest_msg *req = &snp_dev->secret_request;
> + struct snp_guest_msg_hdr *req_hdr = &req->hdr;
> + struct snp_guest_msg_hdr *resp_hdr = &resp->hdr;
> + struct aesgcm_ctx *ctx = snp_dev->ctx;
> + u8 iv[GCM_AES_IV_SIZE] = {};
> +
> + pr_debug("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);
> +
> + /* Copy response from shared memory to encrypted memory. */
> + memcpy(resp, pdata->response, sizeof(*resp));
> +
> + /* 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 + ctx->authsize) > guest_req->resp_sz))
> + return -EBADMSG;
> +
> + /* Decrypt the payload */
> + memcpy(iv, &resp_hdr->msg_seqno, sizeof(resp_hdr->msg_seqno));
> + if (!aesgcm_decrypt(ctx, guest_req->resp_buf, resp->payload, resp_hdr->msg_sz,
> + &resp_hdr->algo, AAD_LEN, iv, resp_hdr->authtag))
> + return -EBADMSG;
> +
> + return 0;
> +}
> +
> +static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, struct snp_guest_req *req)
> +{
> + struct snp_guest_msg *msg = &snp_dev->secret_request;
> + struct snp_guest_msg_hdr *hdr = &msg->hdr;
> + struct aesgcm_ctx *ctx = snp_dev->ctx;
> + u8 iv[GCM_AES_IV_SIZE] = {};
> +
> + memset(msg, 0, sizeof(*msg));
> +
> + hdr->algo = SNP_AEAD_AES_256_GCM;
> + hdr->hdr_version = MSG_HDR_VER;
> + hdr->hdr_sz = sizeof(*hdr);
> + hdr->msg_type = req->msg_type;
> + hdr->msg_version = req->msg_version;
> + hdr->msg_seqno = seqno;
> + hdr->msg_vmpck = req->vmpck_id;
> + hdr->msg_sz = req->req_sz;
> +
> + /* Verify the sequence number is non-zero */
> + if (!hdr->msg_seqno)
> + return -ENOSR;
> +
> + pr_debug("request [seqno %lld type %d version %d sz %d]\n",
> + hdr->msg_seqno, hdr->msg_type, hdr->msg_version, hdr->msg_sz);
> +
> + if (WARN_ON((req->req_sz + ctx->authsize) > sizeof(msg->payload)))
> + return -EBADMSG;
> +
> + memcpy(iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> + aesgcm_encrypt(ctx, msg->payload, req->req_buf, req->req_sz, &hdr->algo,
> + AAD_LEN, iv, hdr->authtag);
> +
> + return 0;
> +}
> +
> +static int __handle_guest_request(struct snp_guest_dev *snp_dev, struct snp_guest_req *req,
> + struct snp_guest_request_ioctl *rio,
> + struct sev_guest_platform_data *pdata)
> +{
> + unsigned long req_start = jiffies;
> + unsigned int override_npages = 0;
> + u64 override_err = 0;
> + int rc;
> +
> +retry_request:
> + /*
> + * Call firmware to process the request. In this function the encrypted
> + * message enters shared memory with the host. So after this call the
> + * sequence number must be incremented or the VMPCK must be deleted to
> + * prevent reuse of the IV.
> + */
> + rc = snp_issue_guest_request(req, &pdata->input, rio);
> + switch (rc) {
> + case -ENOSPC:
> + /*
> + * If the extended guest request fails due to having too
> + * small of a certificate data buffer, retry the same
> + * guest request without the extended data request in
> + * order to increment the sequence number and thus avoid
> + * IV reuse.
> + */
> + override_npages = req->data_npages;
> + req->exit_code = SVM_VMGEXIT_GUEST_REQUEST;
> +
> + /*
> + * Override the error to inform callers the given extended
> + * request buffer size was too small and give the caller the
> + * required buffer size.
> + */
> + override_err = SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN);
> +
> + /*
> + * If this call to the firmware succeeds, the sequence number can
> + * be incremented allowing for continued use of the VMPCK. If
> + * there is an error reflected in the return value, this value
> + * is checked further down and the result will be the deletion
> + * of the VMPCK and the error code being propagated back to the
> + * user as an ioctl() return code.
> + */
> + goto retry_request;
> +
> + /*
> + * The host may return SNP_GUEST_REQ_ERR_BUSY if the request has been
> + * throttled. Retry in the driver to avoid returning and reusing the
> + * message sequence number on a different message.
> + */
> + case -EAGAIN:
> + if (jiffies - req_start > SNP_REQ_MAX_RETRY_DURATION) {
> + rc = -ETIMEDOUT;
> + break;
> + }
> + schedule_timeout_killable(SNP_REQ_RETRY_DELAY);
> + goto retry_request;
> + }
> +
> + /*
> + * Increment the message sequence number. There is no harm in doing
> + * this now because decryption uses the value stored in the response
> + * structure and any failure will wipe the VMPCK, preventing further
> + * use anyway.
> + */
> + snp_inc_msg_seqno(snp_dev);
> +
> + if (override_err) {
> + rio->exitinfo2 = override_err;
> +
> + /*
> + * If an extended guest request was issued and the supplied certificate
> + * buffer was not large enough, a standard guest request was issued to
> + * prevent IV reuse. If the standard request was successful, return -EIO
> + * back to the caller as would have originally been returned.
> + */
> + if (!rc && override_err == SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN))
> + rc = -EIO;
> + }
> +
> + if (override_npages)
> + req->data_npages = override_npages;
> +
> + return rc;
> +}
> +
> +int snp_send_guest_request(struct snp_guest_dev *snp_dev, struct snp_guest_req *req,
> + struct snp_guest_request_ioctl *rio)
> +{
> + struct sev_guest_platform_data *pdata;
> + u64 seqno;
> + int rc;
> +
> + if (!snp_dev || !snp_dev->pdata || !req || !rio)
> return -ENODEV;
>
> - pr_info("SNP guest platform device initialized.\n");
> + pdata = snp_dev->pdata;
> +
> + /* Get message sequence and verify that its a non-zero */
> + seqno = snp_get_msg_seqno(snp_dev);
> + if (!seqno)
> + return -EIO;
> +
> + /* Clear shared memory's response for the host to populate. */
> + memset(pdata->response, 0, sizeof(struct snp_guest_msg));
> +
> + /* Encrypt the userspace provided payload in pdata->secret_request. */
> + rc = enc_payload(snp_dev, seqno, req);
> + if (rc)
> + return rc;
> +
> + /*
> + * Write the fully encrypted request to the shared unencrypted
> + * request page.
> + */
> + memcpy(pdata->request, &snp_dev->secret_request, sizeof(snp_dev->secret_request));
> +
> + rc = __handle_guest_request(snp_dev, req, rio, pdata);
> + if (rc) {
> + if (rc == -EIO &&
> + rio->exitinfo2 == SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN))
> + return rc;
> +
> + pr_alert("Detected error from ASP request. rc: %d, exitinfo2: 0x%llx\n",
> + rc, rio->exitinfo2);
> + snp_disable_vmpck(snp_dev);
> + return rc;
> + }
> +
> + rc = verify_and_dec_payload(snp_dev, req, pdata);
> + if (rc) {
> + pr_alert("Detected unexpected decode failure from ASP. rc: %d\n", rc);
> + snp_disable_vmpck(snp_dev);
> + return rc;
> + }
> +
> return 0;
> }
> -device_initcall(snp_init_platform_device);
> +EXPORT_SYMBOL_GPL(snp_send_guest_request);
> +
> +bool snp_assign_vmpck(struct snp_guest_dev *dev, unsigned int vmpck_id)
> +{
> + if (WARN_ON(vmpck_id > 3))

This constant 3 should be #define'd, I believe.

> + return false;
> +
> + dev->vmpck_id = vmpck_id;
> +
> + return true;
> +}
> +EXPORT_SYMBOL_GPL(snp_assign_vmpck);
> diff --git a/drivers/virt/coco/sev-guest/Kconfig b/drivers/virt/coco/sev-guest/Kconfig
> index 0b772bd921d8..a6405ab6c2c3 100644
> --- a/drivers/virt/coco/sev-guest/Kconfig
> +++ b/drivers/virt/coco/sev-guest/Kconfig
> @@ -2,7 +2,6 @@ config SEV_GUEST
> tristate "AMD SEV Guest driver"
> default m
> depends on AMD_MEM_ENCRYPT
> - select CRYPTO_LIB_AESGCM
> select TSM_REPORTS
> help
> SEV-SNP firmware provides the guest a mechanism to communicate with
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index 0f2134deca51..1cdf7ab04d39 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -31,130 +31,10 @@
>
> #define DEVICE_NAME "sev-guest"
>
> -#define SNP_REQ_MAX_RETRY_DURATION (60*HZ)
> -#define SNP_REQ_RETRY_DELAY (2*HZ)
> -
> -struct snp_guest_dev {
> - struct device *dev;
> - struct miscdevice misc;
> -
> - /* Mutex to serialize the shared buffer access and command handling. */
> - struct mutex cmd_mutex;
> -
> - void *certs_data;
> - struct aesgcm_ctx *ctx;
> - /* request and response are in unencrypted memory */
> - struct snp_guest_msg *request, *response;
> -
> - /*
> - * Avoid information leakage by double-buffering shared messages
> - * in fields that are in regular encrypted memory.
> - */
> - struct snp_guest_msg secret_request, secret_response;
> -
> - struct snp_secrets_page_layout *layout;
> - struct snp_req_data input;
> - union {
> - struct snp_report_req report;
> - struct snp_derived_key_req derived_key;
> - struct snp_ext_report_req ext_report;
> - } req;
> - unsigned int vmpck_id;
> -};
> -
> 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 inline u8 *snp_get_vmpck(struct snp_guest_dev *snp_dev)
> -{
> - return snp_dev->layout->vmpck0 + snp_dev->vmpck_id * VMPCK_KEY_LEN;
> -}
> -
> -static inline u32 *snp_get_os_area_msg_seqno(struct snp_guest_dev *snp_dev)
> -{
> - return &snp_dev->layout->os_area.msg_seqno_0 + snp_dev->vmpck_id;
> -}
> -
> -static bool snp_is_vmpck_empty(struct snp_guest_dev *snp_dev)
> -{
> - char zero_key[VMPCK_KEY_LEN] = {0};
> - u8 *key = snp_get_vmpck(snp_dev);
> -
> - return !memcmp(key, zero_key, VMPCK_KEY_LEN);
> -}
> -
> -/*
> - * If an error is received from the host or AMD Secure Processor (ASP) there
> - * are two options. Either retry the exact same encrypted request or discontinue
> - * using the VMPCK.
> - *
> - * This is because in the current encryption scheme GHCB v2 uses AES-GCM to
> - * encrypt the requests. The IV for this scheme is the sequence number. GCM
> - * cannot tolerate IV reuse.
> - *
> - * The ASP FW v1.51 only increments the sequence numbers on a successful
> - * guest<->ASP back and forth and only accepts messages at its exact sequence
> - * number.
> - *
> - * So if the sequence number were to be reused the encryption scheme is
> - * vulnerable. If the sequence number were incremented for a fresh IV the ASP
> - * will reject the request.
> - */
> -static void snp_disable_vmpck(struct snp_guest_dev *snp_dev)
> -{
> - u8 *key = snp_get_vmpck(snp_dev);
> -
> - dev_alert(snp_dev->dev, "Disabling vmpck_id %u to prevent IV reuse.\n",
> - snp_dev->vmpck_id);
> - memzero_explicit(key, VMPCK_KEY_LEN);
> -}
> -
> -static inline u64 __snp_get_msg_seqno(struct snp_guest_dev *snp_dev)
> -{
> - u32 *os_area_msg_seqno = snp_get_os_area_msg_seqno(snp_dev);
> - u64 count;
> -
> - lockdep_assert_held(&snp_dev->cmd_mutex);
> -
> - /* Read the current message sequence counter from secrets pages */
> - count = *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)
> -{
> - u32 *os_area_msg_seqno = snp_get_os_area_msg_seqno(snp_dev);
> -
> - /*
> - * The counter is also incremented by the PSP, so increment it by 2
> - * and save in secrets page.
> - */
> - *os_area_msg_seqno += 2;
> -}
> -
> static inline struct snp_guest_dev *to_snp_dev(struct file *file)
> {
> struct miscdevice *dev = file->private_data;
> @@ -162,241 +42,6 @@ static inline struct snp_guest_dev *to_snp_dev(struct file *file)
> return container_of(dev, struct snp_guest_dev, misc);
> }
>
> -static struct aesgcm_ctx *snp_init_crypto(struct snp_guest_dev *snp_dev)
> -{
> - struct aesgcm_ctx *ctx;
> - u8 *key;
> -
> - if (snp_is_vmpck_empty(snp_dev)) {
> - pr_err("VM communication key VMPCK%u is null\n", vmpck_id);
> - return NULL;
> - }
> -
> - ctx = kzalloc(sizeof(*ctx), GFP_KERNEL_ACCOUNT);
> - if (!ctx)
> - return NULL;
> -
> - key = snp_get_vmpck(snp_dev);
> - if (aesgcm_expandkey(ctx, key, VMPCK_KEY_LEN, AUTHTAG_LEN)) {
> - pr_err("Crypto context initialization failed\n");
> - kfree(ctx);
> - return NULL;
> - }
> -
> - return ctx;
> -}
> -
> -static int verify_and_dec_payload(struct snp_guest_dev *snp_dev, struct snp_guest_req *guest_req)
> -{
> - struct snp_guest_msg *resp = &snp_dev->secret_response;
> - struct snp_guest_msg *req = &snp_dev->secret_request;
> - struct snp_guest_msg_hdr *req_hdr = &req->hdr;
> - struct snp_guest_msg_hdr *resp_hdr = &resp->hdr;
> - struct aesgcm_ctx *ctx = snp_dev->ctx;
> - u8 iv[GCM_AES_IV_SIZE] = {};
> -
> - pr_debug("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);
> -
> - /* Copy response from shared memory to encrypted memory. */
> - memcpy(resp, snp_dev->response, sizeof(*resp));
> -
> - /* 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 + ctx->authsize) > guest_req->resp_sz))
> - return -EBADMSG;
> -
> - /* Decrypt the payload */
> - memcpy(iv, &resp_hdr->msg_seqno, sizeof(resp_hdr->msg_seqno));
> - if (!aesgcm_decrypt(ctx, guest_req->resp_buf, resp->payload, resp_hdr->msg_sz,
> - &resp_hdr->algo, AAD_LEN, iv, resp_hdr->authtag))
> - return -EBADMSG;
> -
> - return 0;
> -}
> -
> -static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, struct snp_guest_req *req)
> -{
> - struct snp_guest_msg *msg = &snp_dev->secret_request;
> - struct snp_guest_msg_hdr *hdr = &msg->hdr;
> - struct aesgcm_ctx *ctx = snp_dev->ctx;
> - u8 iv[GCM_AES_IV_SIZE] = {};
> -
> - memset(msg, 0, sizeof(*msg));
> -
> - hdr->algo = SNP_AEAD_AES_256_GCM;
> - hdr->hdr_version = MSG_HDR_VER;
> - hdr->hdr_sz = sizeof(*hdr);
> - hdr->msg_type = req->msg_type;
> - hdr->msg_version = req->msg_version;
> - hdr->msg_seqno = seqno;
> - hdr->msg_vmpck = req->vmpck_id;
> - hdr->msg_sz = req->req_sz;
> -
> - /* Verify the sequence number is non-zero */
> - if (!hdr->msg_seqno)
> - return -ENOSR;
> -
> - pr_debug("request [seqno %lld type %d version %d sz %d]\n",
> - hdr->msg_seqno, hdr->msg_type, hdr->msg_version, hdr->msg_sz);
> -
> - if (WARN_ON((req->req_sz + ctx->authsize) > sizeof(msg->payload)))
> - return -EBADMSG;
> -
> - memcpy(iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
> - aesgcm_encrypt(ctx, msg->payload, req->req_buf, req->req_sz, &hdr->algo,
> - AAD_LEN, iv, hdr->authtag);
> -
> - return 0;
> -}
> -
> -static int __handle_guest_request(struct snp_guest_dev *snp_dev, struct snp_guest_req *req,
> - struct snp_guest_request_ioctl *rio)
> -{
> - unsigned long req_start = jiffies;
> - unsigned int override_npages = 0;
> - u64 override_err = 0;
> - int rc;
> -
> -retry_request:
> - /*
> - * Call firmware to process the request. In this function the encrypted
> - * message enters shared memory with the host. So after this call the
> - * sequence number must be incremented or the VMPCK must be deleted to
> - * prevent reuse of the IV.
> - */
> - rc = snp_issue_guest_request(req, &snp_dev->input, rio);
> - switch (rc) {
> - case -ENOSPC:
> - /*
> - * If the extended guest request fails due to having too
> - * small of a certificate data buffer, retry the same
> - * guest request without the extended data request in
> - * order to increment the sequence number and thus avoid
> - * IV reuse.
> - */
> - override_npages = req->data_npages;
> - req->exit_code = SVM_VMGEXIT_GUEST_REQUEST;
> -
> - /*
> - * Override the error to inform callers the given extended
> - * request buffer size was too small and give the caller the
> - * required buffer size.
> - */
> - override_err = SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN);
> -
> - /*
> - * If this call to the firmware succeeds, the sequence number can
> - * be incremented allowing for continued use of the VMPCK. If
> - * there is an error reflected in the return value, this value
> - * is checked further down and the result will be the deletion
> - * of the VMPCK and the error code being propagated back to the
> - * user as an ioctl() return code.
> - */
> - goto retry_request;
> -
> - /*
> - * The host may return SNP_GUEST_VMM_ERR_BUSY if the request has been
> - * throttled. Retry in the driver to avoid returning and reusing the
> - * message sequence number on a different message.
> - */
> - case -EAGAIN:
> - if (jiffies - req_start > SNP_REQ_MAX_RETRY_DURATION) {
> - rc = -ETIMEDOUT;
> - break;
> - }
> - schedule_timeout_killable(SNP_REQ_RETRY_DELAY);
> - goto retry_request;
> - }
> -
> - /*
> - * Increment the message sequence number. There is no harm in doing
> - * this now because decryption uses the value stored in the response
> - * structure and any failure will wipe the VMPCK, preventing further
> - * use anyway.
> - */
> - snp_inc_msg_seqno(snp_dev);
> -
> - if (override_err) {
> - rio->exitinfo2 = override_err;
> -
> - /*
> - * If an extended guest request was issued and the supplied certificate
> - * buffer was not large enough, a standard guest request was issued to
> - * prevent IV reuse. If the standard request was successful, return -EIO
> - * back to the caller as would have originally been returned.
> - */
> - if (!rc && override_err == SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN))
> - rc = -EIO;
> - }
> -
> - if (override_npages)
> - req->data_npages = override_npages;
> -
> - return rc;
> -}
> -
> -static int snp_send_guest_request(struct snp_guest_dev *snp_dev, struct snp_guest_req *req,
> - struct snp_guest_request_ioctl *rio)
> -{
> - 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;
> -
> - /* Clear shared memory's response for the host to populate. */
> - memset(snp_dev->response, 0, sizeof(struct snp_guest_msg));
> -
> - /* Encrypt the userspace provided payload in snp_dev->secret_request. */
> - rc = enc_payload(snp_dev, seqno, req);
> - if (rc)
> - return rc;
> -
> - /*
> - * Write the fully encrypted request to the shared unencrypted
> - * request page.
> - */
> - memcpy(snp_dev->request, &snp_dev->secret_request,
> - sizeof(snp_dev->secret_request));
> -
> - rc = __handle_guest_request(snp_dev, req, rio);
> - if (rc) {
> - if (rc == -EIO &&
> - rio->exitinfo2 == SNP_GUEST_VMM_ERR(SNP_GUEST_VMM_ERR_INVALID_LEN))
> - return rc;
> -
> - dev_alert(snp_dev->dev,
> - "Detected error from ASP request. rc: %d, exitinfo2: 0x%llx\n",
> - rc, rio->exitinfo2);
> - snp_disable_vmpck(snp_dev);
> - return rc;
> - }
> -
> - rc = verify_and_dec_payload(snp_dev, req);
> - if (rc) {
> - dev_alert(snp_dev->dev, "Detected unexpected decode failure from ASP. rc: %d\n", rc);
> - snp_disable_vmpck(snp_dev);
> - return rc;
> - }
> -
> - return 0;
> -}
> -
> struct snp_req_resp {
> sockptr_t req_data;
> sockptr_t resp_data;
> @@ -607,7 +252,7 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
> mutex_lock(&snp_dev->cmd_mutex);
>
> /* Check if the VMPCK is not empty */
> - if (snp_is_vmpck_empty(snp_dev)) {
> + if (snp_is_vmpck_empty(snp_dev->vmpck_id)) {
> dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
> mutex_unlock(&snp_dev->cmd_mutex);
> return -ENOTTY;
> @@ -642,58 +287,11 @@ static long snp_guest_ioctl(struct file *file, unsigned int ioctl, unsigned long
> 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(struct device *dev, 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 (!page)
> - return NULL;
> -
> - ret = set_memory_decrypted((unsigned long)page_address(page), npages);
> - if (ret) {
> - dev_err(dev, "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,
> };
>
> -bool snp_assign_vmpck(struct snp_guest_dev *dev, unsigned int vmpck_id)
> -{
> - if (WARN_ON(vmpck_id > 3))
> - return false;
> -
> - dev->vmpck_id = vmpck_id;
> -
> - return true;
> -}
> -
> struct snp_msg_report_resp_hdr {
> u32 status;
> u32 report_size;
> @@ -727,7 +325,7 @@ static int sev_report_new(struct tsm_report *report, void *data)
> guard(mutex)(&snp_dev->cmd_mutex);
>
> /* Check if the VMPCK is not empty */
> - if (snp_is_vmpck_empty(snp_dev)) {
> + if (snp_is_vmpck_empty(snp_dev->vmpck_id)) {
> dev_err_ratelimited(snp_dev->dev, "VMPCK is disabled\n");
> return -ENOTTY;
> }
> @@ -820,76 +418,43 @@ static void unregister_sev_tsm(void *data)
>
> static int __init sev_guest_probe(struct platform_device *pdev)
> {
> - struct snp_secrets_page_layout *layout;
> - struct sev_guest_platform_data *data;
> struct device *dev = &pdev->dev;
> struct snp_guest_dev *snp_dev;
> struct miscdevice *misc;
> - void __iomem *mapping;
> int ret;
>
> if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
> return -ENODEV;
>
> - if (!dev->platform_data)
> - return -ENODEV;
> -
> - data = (struct sev_guest_platform_data *)dev->platform_data;
> - mapping = ioremap_encrypted(data->secrets_gpa, PAGE_SIZE);
> - if (!mapping)
> - return -ENODEV;
> -
> - layout = (__force void *)mapping;
> -
> - ret = -ENOMEM;
> snp_dev = devm_kzalloc(&pdev->dev, sizeof(struct snp_guest_dev), GFP_KERNEL);
> if (!snp_dev)
> - goto e_unmap;
> + return -ENOMEM;
>
> - ret = -EINVAL;
> - snp_dev->layout = layout;
> if (!snp_assign_vmpck(snp_dev, vmpck_id)) {
> dev_err(dev, "invalid vmpck id %u\n", vmpck_id);
> - goto e_unmap;
> + ret = -EINVAL;
> + goto e_free_snpdev;
> }
>
> - /* Verify that VMPCK is not zero. */
> - if (snp_is_vmpck_empty(snp_dev)) {
> - dev_err(dev, "vmpck id %u is null\n", vmpck_id);
> - goto e_unmap;
> + if (snp_setup_psp_messaging(snp_dev)) {
> + dev_err(dev, "Unable to setup PSP messaging vmpck id %u\n", snp_dev->vmpck_id);
> + ret = -ENODEV;
> + goto e_free_snpdev;
> }
>
> mutex_init(&snp_dev->cmd_mutex);
> platform_set_drvdata(pdev, snp_dev);
> snp_dev->dev = dev;
>
> - /* Allocate the shared page used for the request and response message. */
> - snp_dev->request = alloc_shared_pages(dev, sizeof(struct snp_guest_msg));
> - if (!snp_dev->request)
> - goto e_unmap;
> -
> - snp_dev->response = alloc_shared_pages(dev, sizeof(struct snp_guest_msg));
> - if (!snp_dev->response)
> - goto e_free_request;
> -
> - snp_dev->certs_data = alloc_shared_pages(dev, SEV_FW_BLOB_MAX_SIZE);
> + snp_dev->certs_data = alloc_shared_pages(SEV_FW_BLOB_MAX_SIZE);
> if (!snp_dev->certs_data)
> - goto e_free_response;
> -
> - ret = -EIO;
> - snp_dev->ctx = snp_init_crypto(snp_dev);
> - if (!snp_dev->ctx)
> - goto e_free_cert_data;
> + goto e_free_ctx;
>
> 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 = tsm_register(&sev_tsm_ops, snp_dev, &tsm_report_extra_type);
> if (ret)
> goto e_free_cert_data;
> @@ -900,21 +465,18 @@ static int __init sev_guest_probe(struct platform_device *pdev)
>
> ret = misc_register(misc);
> if (ret)
> - goto e_free_ctx;
> + goto e_free_cert_data;
> +
> + dev_info(dev, "Initialized SEV guest driver (using vmpck_id %u)\n", snp_dev->vmpck_id);
>
> - dev_info(dev, "Initialized SEV guest driver (using vmpck_id %u)\n", vmpck_id);
> return 0;
>
> -e_free_ctx:
> - kfree(snp_dev->ctx);
> e_free_cert_data:
> free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE);
> -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(mapping);
> +e_free_ctx:
> + kfree(snp_dev->ctx);
> +e_free_snpdev:
> + kfree(snp_dev);
> return ret;
> }
>
> @@ -923,10 +485,9 @@ static int __exit sev_guest_remove(struct platform_device *pdev)
> struct snp_guest_dev *snp_dev = platform_get_drvdata(pdev);
>
> free_shared_pages(snp_dev->certs_data, SEV_FW_BLOB_MAX_SIZE);
> - free_shared_pages(snp_dev->response, sizeof(struct snp_guest_msg));
> - free_shared_pages(snp_dev->request, sizeof(struct snp_guest_msg));
> - kfree(snp_dev->ctx);
> misc_deregister(&snp_dev->misc);
> + kfree(snp_dev->ctx);
> + kfree(snp_dev);
>
> return 0;
> }
> --
> 2.34.1
>

--
-Dionna Glaze, PhD (she/her)