[PATCH v8 5/5] x86/tdx: Add Quote generation support

Kuppuswamy Sathyanarayanan
2022-06-09T02:53:10Z

In TDX guest, the second stage in attestation process is to send the
TDREPORT to QE/QGS to generate the TD Quote. For platforms that does
not support communication channels like vsock or TCP/IP, implement
support to get TD Quote using hypercall. GetQuote hypercall can be used
by the TD guest to request VMM facilitate the Quote generation via
QE/QGS. More details about GetQuote hypercall can be found in TDX
Guest-Host Communication Interface (GHCI) for Intel TDX 1.0, section
titled "TDG.VP.VMCALL<GetQuote>.

Since GetQuote is an asynchronous request hypercall, it will not block
till the TD Quote is generated. So VMM uses callback interrupt vector
configured by SetupEventNotifyInterrupt hypercall to notify the guest
about Quote generation completion or failure.

GetQuote TDVMCALL requires TD guest pass a 4K aligned shared buffer
with TDREPORT data as input, which is further used by the VMM to copy
the TD Quote result after successful Quote generation. To create the
shared buffer without breaking the direct map, allocate physically
contiguous kernel memory and create a virtual mapping for it using
vmap(). set_memory_*crypted_noalias() functions can be used to share or
unshare the vmapped page without affecting the direct map.

Also note that, shared buffer allocation is currently handled in IOCTL
handler, although it will increase the TDX_CMD_GET_QUOTE IOCTL response
time, it is negligible compared to the time required for the quote
generation completion. So IOCTL performance optimization is not
considered at this time.

For shared buffer allocation, alternatives like using the DMA API is
also considered. Although it simpler to use, it is not preferred because
dma_alloc_*() APIs require a valid bus device as argument, which would
need converting the attestation driver into a platform device driver.
This is unnecessary, and since the attestation driver does not do real
DMA, there is no need to use real DMA APIs.

Add support for TDX_CMD_GET_QUOTE IOCTL to allow attestation agent
submit GetQuote requests from the user space. Since Quote generation
is an asynchronous request, IOCTL will block indefinitely for the VMM
response in wait_for_completion_interruptible() call. Using this call
will also add an option for the user to end the current request
prematurely by raising any signals. This can be used by attestation
agent to implement Quote generation timeout feature. If attestation
agent is aware of time it can validly wait for QE/QGS response, then
a possible timeout support can be implemented in the user application
using signals. Quote generation timeout feature is currently not
implemented in the driver because the current TDX specification does
not have any recommendation for it.

After submitting the GetQuote request using hypercall, the shared buffer
allocated for the current request is owned by the VMM. So, during this
wait window, if the user terminates the request by raising a signal or
by terminating the application, add a logic to do the memory cleanup
after receiving the VMM response at a later time. Such memory cleanup
support requires accepting the page again using TDX_ACCEPT_PAGE TDX
Module call. So to not overload the callback IRQ handler, move the
callback handler logic to a separate work queue.

To support parallel GetQuote requests, use linked list to track the
active GetQuote requests and upon receiving the callback IRQ, loop
through the active requests and mark the processed requests complete.
Users can open multiple instances of the attestation device and send
GetQuote requests in parallel.

Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
arch/x86/coco/tdx/attest.c | 304 ++++++++++++++++++++++++++++++++
arch/x86/include/uapi/asm/tdx.h | 45 +++++
2 files changed, 349 insertions(+)

diff --git a/arch/x86/coco/tdx/attest.c b/arch/x86/coco/tdx/attest.c
index 24db0bad4923..a2a94622922c 100644
--- a/arch/x86/coco/tdx/attest.c
+++ b/arch/x86/coco/tdx/attest.c
@@ -13,16 +13,56 @@
#include <linux/miscdevice.h>
#include <linux/mm.h>
#include <linux/io.h>
+#include <linux/set_memory.h>
+#include <linux/mutex.h>
#include <asm/tdx.h>
+#include <asm/coco.h>
#include <uapi/asm/tdx.h>

#define DRIVER_NAME "tdx-attest"

/* TDREPORT module call leaf ID */
#define TDX_GET_REPORT 4
+/* GetQuote hypercall leaf ID */
+#define TDVMCALL_GET_QUOTE 0x10002
+
+/* Used for buffer allocation in GetQuote request */
+struct quote_buf {
+ /* vmapped address of kernel buffer (size is page aligned) */
+ void *vmaddr;
+ /* Number of pages */
+ int count;
+};
+
+/* List entry of quote_list */
+struct quote_entry {
+ /* Flag to check validity of the GetQuote request */
+ bool valid;
+ /* Kernel buffer to share data with VMM */
+ struct quote_buf buf;
+ /* Completion object to track completion of GetQuote request */
+ struct completion compl;
+ struct list_head list;
+};

static struct miscdevice miscdev;

+/*
+ * To support parallel GetQuote requests, use the list
+ * to track active GetQuote requests.
+ */
+static LIST_HEAD(quote_list);
+
+/* Lock to protect quote_list */
+static DEFINE_MUTEX(quote_lock);
+
+/*
+ * Workqueue to handle Quote data after Quote generation
+ * notification from VMM.
+ */
+struct workqueue_struct *quote_wq;
+struct work_struct quote_work;
+
static long tdx_get_report(void __user *argp)
{
void *reportdata = NULL, *tdreport = NULL;
@@ -71,6 +111,260 @@ static long tdx_get_report(void __user *argp)
return ret;
}

+/* tdx_get_quote_hypercall() - Request to get TD Quote using TDREPORT */
+static long tdx_get_quote_hypercall(struct quote_buf *buf)
+{
+ struct tdx_hypercall_args args = {0};
+
+ args.r10 = TDX_HYPERCALL_STANDARD;
+ args.r11 = TDVMCALL_GET_QUOTE;
+ args.r12 = cc_mkdec(page_to_phys(vmalloc_to_page(buf->vmaddr)));
+ args.r13 = buf->count * PAGE_SIZE;
+
+ /*
+ * Pass the physical address of TDREPORT to the VMM and
+ * trigger the Quote generation. It is not a blocking
+ * call, hence completion of this request will be notified to
+ * the TD guest via a callback interrupt. More info about ABI
+ * can be found in TDX Guest-Host-Communication Interface
+ * (GHCI), sec titled "TDG.VP.VMCALL<GetQuote>".
+ */
+ return __tdx_hypercall(&args, 0);
+}
+
+/*
+ * init_quote_buf() - Initialize the quote buffer by allocating
+ * a shared buffer of given size.
+ *
+ * Size is page aligned and the allocated memory is decrypted
+ * to allow VMM to access it. Uses VMAP to create a virtual
+ * mapping, which is further used to create a shared mapping
+ * for the buffer without affecting the direct map.
+ */
+static int init_quote_buf(struct quote_buf *buf, u64 req_size)
+{
+ int size = PAGE_ALIGN(req_size);
+ void *addr = NULL, *vmaddr = NULL;
+ int count = size >> PAGE_SHIFT;
+ struct page **pages = NULL;
+ int i;
+
+ addr = alloc_pages_exact(size, GFP_KERNEL);
+ if (!addr)
+ return -ENOMEM;
+
+ /* Allocate mem for array of page ptrs */
+ pages = kcalloc(count, sizeof(*pages), GFP_KERNEL);
+ if (!pages) {
+ free_pages_exact(addr, size);
+ return -ENOMEM;
+ }
+
+ for (i = 0; i < count; i++)
+ pages[i] = virt_to_page(addr + i * PAGE_SIZE);
+
+ /*
+ * Use VMAP to create a virtual mapping, which is used
+ * to create shared mapping without affecting the
+ * direct map. Use VM_MAP_PUT_PAGES to allow vmap()
+ * responsible for freeing the pages when using vfree().
+ */
+ vmaddr = vmap(pages, count, VM_MAP_PUT_PAGES, PAGE_KERNEL);
+ if (!vmaddr) {
+ kfree(pages);
+ free_pages_exact(addr, size);
+ return -EIO;
+ }
+
+ /* Use noalias variant to not affect the direct mapping */
+ if (set_memory_decrypted_noalias((unsigned long)vmaddr, count)) {
+ vfree(vmaddr);
+ return -EIO;
+ }
+
+ buf->vmaddr = vmaddr;
+ buf->count = count;
+
+ return 0;
+}
+
+/* Remove the shared mapping and free the memory */
+static void deinit_quote_buf(struct quote_buf *buf)
+{
+ if (!buf)
+ return;
+
+ /* Mark pages private */
+ if (set_memory_encrypted_noalias((unsigned long)buf->vmaddr,
+ buf->count)) {
+ pr_warn("Failed to encrypt %d pages at %p", buf->count,
+ buf->vmaddr);
+ return;
+ }
+
+ vfree(buf->vmaddr);
+}
+
+static struct quote_entry *alloc_quote_entry(u64 buf_len)
+{
+ struct quote_entry *entry = NULL;
+
+ entry = kmalloc(sizeof(*entry), GFP_KERNEL);
+ if (!entry)
+ return NULL;
+
+ /* Init buffer for quote request */
+ if (init_quote_buf(&entry->buf, buf_len)) {
+ kfree(entry);
+ return NULL;
+ }
+
+ init_completion(&entry->compl);
+ entry->valid = true;
+
+ return entry;
+}
+
+static void free_quote_entry(struct quote_entry *entry)
+{
+ deinit_quote_buf(&entry->buf);
+ kfree(entry);
+}
+
+/* Must be called with quote_lock held */
+static void _del_quote_entry(struct quote_entry *entry)
+{
+ list_del(&entry->list);
+ free_quote_entry(entry);
+}
+
+static void del_quote_entry(struct quote_entry *entry)
+{
+ mutex_lock(&quote_lock);
+ _del_quote_entry(entry);
+ mutex_unlock(&quote_lock);
+}
+
+/* Handles early termination of GetQuote requests */
+void terminate_quote_request(struct quote_entry *entry)
+{
+ struct tdx_quote_hdr *quote_hdr;
+
+ /*
+ * For early termination, if the request is not yet
+ * processed by VMM (GET_QUOTE_IN_FLIGHT), the VMM
+ * still owns the shared buffer, so mark the request
+ * invalid to let quote_callback_handler() handle the
+ * memory cleanup function. If the request is already
+ * processed, then do the cleanup and return.
+ */
+
+ mutex_lock(&quote_lock);
+ quote_hdr = (struct tdx_quote_hdr *)entry->buf.vmaddr;
+ if (quote_hdr->status == GET_QUOTE_IN_FLIGHT) {
+ entry->valid = false;
+ mutex_unlock(&quote_lock);
+ return;
+ }
+ _del_quote_entry(entry);
+ mutex_unlock(&quote_lock);
+}
+
+static long tdx_get_quote(void __user *argp)
+{
+ struct quote_entry *entry;
+ struct tdx_quote_req req;
+ struct quote_buf *buf;
+ long ret;
+
+ /* Copy GetQuote request struct from user buffer */
+ if (copy_from_user(&req, argp, sizeof(struct tdx_quote_req)))
+ return -EFAULT;
+
+ /* Make sure the length is valid */
+ if (!req.len)
+ return -EINVAL;
+
+ entry = alloc_quote_entry(req.len);
+ if (!entry)
+ return -ENOMEM;
+
+ buf = &entry->buf;
+
+ /* Copy TDREPORT from user buffer to kernel Quote buffer */
+ if (copy_from_user(buf->vmaddr, (void __user *)req.buf, req.len)) {
+ free_quote_entry(entry);
+ return -EFAULT;
+ }
+
+ mutex_lock(&quote_lock);
+
+ /* Submit GetQuote Request */
+ ret = tdx_get_quote_hypercall(buf);
+ if (ret) {
+ mutex_unlock(&quote_lock);
+ pr_err("GetQuote hypercall failed, status:%lx\n", ret);
+ free_quote_entry(entry);
+ return -EIO;
+ }
+
+ /* Add current quote entry to quote_list to track active requests */
+ list_add_tail(&entry->list, &quote_list);
+
+ mutex_unlock(&quote_lock);
+
+ /* Wait for attestation completion */
+ ret = wait_for_completion_interruptible(&entry->compl);
+ if (ret < 0) {
+ terminate_quote_request(entry);
+ return -EINTR;
+ }
+
+ /*
+ * If GetQuote request completed successfully, copy the result
+ * back to the user and do the cleanup.
+ */
+ if (copy_to_user((void __user *)req.buf, buf->vmaddr, req.len))
+ ret = -EFAULT;
+
+ /*
+ * Reaching here means GetQuote request is processed
+ * successfully. So do the cleanup and return 0.
+ */
+ del_quote_entry(entry);
+
+ return 0;
+}
+
+static void attestation_callback_handler(void)
+{
+ queue_work(quote_wq, &quote_work);
+}
+
+static void quote_callback_handler(struct work_struct *work)
+{
+ struct tdx_quote_hdr *quote_hdr;
+ struct quote_entry *entry, *next;
+
+ /* Find processed quote request and mark it complete */
+ mutex_lock(&quote_lock);
+ list_for_each_entry_safe(entry, next, &quote_list, list) {
+ quote_hdr = (struct tdx_quote_hdr *)entry->buf.vmaddr;
+ if (quote_hdr->status == GET_QUOTE_IN_FLIGHT)
+ continue;
+ /*
+ * If user invalidated the current request, remove the
+ * entry from the quote list and free it. If the request
+ * is still valid, mark it complete.
+ */
+ if (entry->valid)
+ complete(&entry->compl);
+ else
+ _del_quote_entry(entry);
+ }
+ mutex_unlock(&quote_lock);
+}
+
static long tdx_attest_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
@@ -81,6 +375,9 @@ static long tdx_attest_ioctl(struct file *file, unsigned int cmd,
case TDX_CMD_GET_REPORT:
ret = tdx_get_report(argp);
break;
+ case TDX_CMD_GET_QUOTE:
+ ret = tdx_get_quote(argp);
+ break;
default:
pr_debug("cmd %d not supported\n", cmd);
break;
@@ -103,6 +400,13 @@ static int __init tdx_attestation_init(void)
if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
return -EIO;

+ quote_wq = create_singlethread_workqueue("tdx_quote_handler");
+
+ INIT_WORK(&quote_work, quote_callback_handler);
+
+ /* Register attestation event notify handler */
+ tdx_setup_ev_notify_handler(attestation_callback_handler);
+
miscdev.name = DRIVER_NAME;
miscdev.minor = MISC_DYNAMIC_MINOR;
miscdev.fops = &tdx_attest_fops;
diff --git a/arch/x86/include/uapi/asm/tdx.h b/arch/x86/include/uapi/asm/tdx.h
index 8b57dea67eab..51944dd0462f 100644
--- a/arch/x86/include/uapi/asm/tdx.h
+++ b/arch/x86/include/uapi/asm/tdx.h
@@ -39,4 +39,49 @@ struct tdx_report_req {
*/
#define TDX_CMD_GET_REPORT _IOWR('T', 0x01, struct tdx_report_req)

+/* struct tdx_quote_req: Request to generate TD Quote using TDREPORT
+ *
+ * @buf : Pass user data that includes TDREPORT as input. Upon
+ * successful completion of IOCTL, output is copied
+ * back to the same buffer.
+ * @len : Length of the buffer.
+ */
+struct tdx_quote_req {
+ __u64 buf;
+ __u64 len;
+};
+
+/*
+ * TDX_CMD_GET_QUOTE - Get TD Quote from QE/QGS using GetQuote
+ * TDVMCALL.
+ *
+ * Returns 0 on success, -EINTR for interrupted request, and
+ * standard errono on other failures.
+ */
+#define TDX_CMD_GET_QUOTE _IOR('T', 0x02, struct tdx_quote_req)
+
+/* TD Quote status codes */
+#define GET_QUOTE_SUCCESS 0
+#define GET_QUOTE_IN_FLIGHT 0xffffffffffffffff
+#define GET_QUOTE_ERROR 0x8000000000000000
+#define GET_QUOTE_SERVICE_UNAVAILABLE 0x8000000000000001
+
+/*
+ * Format of Quote data header. More details can be found in TDX
+ * Guest-Host Communication Interface (GHCI) for Intel TDX 1.0,
+ * section titled "TDG.VP.VMCALL<GetQuote>"
+ */
+struct tdx_quote_hdr {
+ /* Quote version, filled by TD */
+ __u64 version;
+ /* Status code of Quote request, filled by VMM */
+ __u64 status;
+ /* Length of TDREPORT, filled by TD */
+ __u32 in_len;
+ /* Length of Quote, filled by VMM */
+ __u32 out_len;
+ /* Actual Quote data */
+ __u64 data[0];
+};
+
#endif /* _UAPI_ASM_X86_TDX_H */
--
2.25.1