On 10/30/23 01:36, Nikunj A Dadhania 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 an
API to the driver to assign key and send guest request.
Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
---
arch/x86/Kconfig | 1 +
arch/x86/include/asm/sev-guest.h | 84 +++-
arch/x86/include/asm/sev.h | 10 -
arch/x86/kernel/sev.c | 466 ++++++++++++++++++++++-
drivers/virt/coco/sev-guest/Kconfig | 1 -
drivers/virt/coco/sev-guest/sev-guest.c | 486 +-----------------------
6 files changed, 555 insertions(+), 493 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 66bfabae8814..245a18f6910a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1509,6 +1509,7 @@ 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 22ef97b55069..e6f94208173d 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 +63,45 @@ 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, *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, secret_response;
+
+ struct sev_guest_platform_data *pdata;
+ unsigned int vmpck_id;
+};
+
struct snp_guest_req {
void *req_buf, *resp_buf, *data;
size_t req_sz, resp_sz, *data_npages;
@@ -72,6 +111,47 @@ 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 void free_shared_pages(void *buf, size_t sz)
These should probably be marked __inline if you're going to define them in
a header file.
+{
+ 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 (!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 fd3b822fa9e7..fb3b1feb1b84 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>
@@ -941,6 +942,457 @@ static void snp_cleanup_vmsa(struct sev_es_save_area *vmsa)
free_page((unsigned long)vmsa);
}
+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 %d 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;
+ }
I probably missed this in the other patch or even when the driver was
first created, but shouldn't we have a lockdep_assert_held() here, too,
before updating the count?
+
+ /*
+ * 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("SNP: vmpck id %d 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("SNP: crypto init 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)) {
+ 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 no secrets page\n");
Maybe "SNP secrets page not found\n" ?
+ return -ENODEV;
+ }
+
+ pdata = kzalloc(sizeof(struct sev_guest_platform_data), GFP_KERNEL);
+ if (!pdata) {
+ pr_err("SNP alloc failed\n");
Maybe "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("Unable to locate AP jump table address: failed to map the SNP secrets page.\n");
Maybe "Failed to map SNP secrets page\n" ? Not sure where the AP jump
table came in on this...
+ 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 init crypto failed\n");
Maybe "SNP crypto context initialization failed\n" ?
+ platform_data = NULL;
+ goto e_free_response;
+ }
+
+ snp_dev->pdata = platform_data;
Add a blank line here.
+ 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 __enc_payload(struct aesgcm_ctx *ctx, struct snp_guest_msg *msg,
+ void *plaintext, size_t len)
+{
+ struct snp_guest_msg_hdr *hdr = &msg->hdr;
+ u8 iv[GCM_AES_IV_SIZE] = {};
+
+ if (WARN_ON((hdr->msg_sz + ctx->authsize) > sizeof(msg->payload)))
+ return -EBADMSG;
+
+ memcpy(iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
+ aesgcm_encrypt(ctx, msg->payload, plaintext, len, &hdr->algo, AAD_LEN,
+ iv, hdr->authtag);
+ return 0;
+}
+
+static int dec_payload(struct aesgcm_ctx *ctx, struct snp_guest_msg *msg,
+ void *plaintext, size_t len)
+{
+ struct snp_guest_msg_hdr *hdr = &msg->hdr;
+ u8 iv[GCM_AES_IV_SIZE] = {};
+
+ memcpy(iv, &hdr->msg_seqno, sizeof(hdr->msg_seqno));
+ if (aesgcm_decrypt(ctx, plaintext, msg->payload, len, &hdr->algo,
+ AAD_LEN, iv, hdr->authtag))
+ return 0;
+ else
+ return -EBADMSG;
+}
+
+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;
+
+ 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;
+
+ return dec_payload(ctx, resp, guest_req->resp_buf, resp_hdr->msg_sz);
+}
+
+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;
+
+ 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);
+
+ return __enc_payload(snp_dev->ctx, msg, req->req_buf, req->req_sz);
+}
+
+static int snp_issue_guest_request(struct snp_guest_req *req, struct snp_req_data *input,
+ struct snp_guest_request_ioctl *rio);
Could all of these routines been moved down closer to the bottom of the
file to avoid this forward declaration?
+
+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;
+
...
-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;
}
@@ -780,11 +332,9 @@ 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);
Looks like this one should still be here, right?
Thanks,
Tom
- 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;
}
