From ff07451280ba839c34d56b9a7d8d834ebf078677 Mon Sep 17 00:00:00 2001
From: Michael Scire <SciresM@gmail.com>
Date: Mon, 19 Feb 2018 20:18:53 -0800
Subject: [PATCH] Outline user<->secure page copying.

---
 exosphere/smc_api.c  | 16 +++++++++++-
 exosphere/userpage.c | 62 ++++++++++++++++++++++++++++++++++++++++++++
 exosphere/userpage.h | 22 ++++++++++++++++
 3 files changed, 99 insertions(+), 1 deletion(-)
 create mode 100644 exosphere/userpage.c
 create mode 100644 exosphere/userpage.h

diff --git a/exosphere/smc_api.c b/exosphere/smc_api.c
index 1f3038d6e..db5f804cf 100644
--- a/exosphere/smc_api.c
+++ b/exosphere/smc_api.c
@@ -6,6 +6,7 @@
 #include "smc_api.h"
 #include "smc_user.h"
 #include "se.h"
+#include "userpage.h"
 
 #define SMC_USER_HANDLERS 0x13
 #define SMC_PRIV_HANDLERS 0x9
@@ -225,6 +226,10 @@ uint32_t smc_check_status(smc_args_t *args) {
 uint32_t smc_get_result(smc_args_t *) {
     uint32_t status;
     unsigned char result_buf[0x400];
+    upage_ref_t page_ref;
+    
+    void *user_address = (void *)args->X[2];
+    
     if (g_smc_callback_key == 0) {
         return 4;
     }
@@ -241,7 +246,16 @@ uint32_t smc_get_result(smc_args_t *) {
     args->X[1] = g_smc_callback(result_buf, args->X[3]);
     g_smc_callback_key = 0;
     
-    /* TODO: Copy result from result_buf into output in args->X[2] */
+    /* Initialize page reference. */
+    if (upage_init(&page_ref, user_address) == 0) {
+        return 2;
+    }
+
+    /* Copy result output back to user. */
+    if (secure_copy_to_user(&page_ref, user_address, result_buf, (size_t)args->X[3]) == 0) {
+        return 2;
+    }
+    
     return 0;
 }
 
diff --git a/exosphere/userpage.c b/exosphere/userpage.c
new file mode 100644
index 000000000..5099a8a0a
--- /dev/null
+++ b/exosphere/userpage.c
@@ -0,0 +1,62 @@
+#include <stdint.h>
+
+#include "utils.h"
+#include "userpage.h"
+
+uint64_t g_secure_page_user_address = NULL;
+
+/* Create a user page reference for the desired address. */
+/* Returns 1 on success, 0 on failure. */
+int upage_init(upage_ref_t *upage, void *user_address) {
+    upage->user_page = get_page_for_address(user_address);
+    upage->secure_page = 0ULL;
+    
+    if (g_secure_page_user_address != NULL) {
+        /* Different ASLR'd address indicate SPL was rebooted. Panic. */
+        if (g_secure_page_user_address != upage->user_page) {
+            panic();
+        }
+        upage->secure_page = SECURE_USER_PAGE_ADDR;
+    } else {
+        /* Official (weak) validation for SPL's ASLR'd address. */
+        if (upage->user_page >> 31) {
+            g_secure_page_user_address = upage->user_page;
+            /* TODO: Map this page into the MMU and invalidate the TLB. */
+            upage->secure_page = SECURE_USER_PAGE_ADDR;
+        }
+    }
+    
+    return upage->secure_page != 0ULL;
+}
+
+int user_copy_to_secure(upage_ref_t *upage, void *secure_dst, void *user_src, size_t size) {    
+    /* Fail if the page doesn't match. */
+    if (get_page_for_address(user_src) != upage->user_page) {
+        return 0;
+    }
+    
+    /* Fail if we go past the page boundary. */
+    if (size != 0 && get_page_for_address(user_src + size - 1) != upage->user_page) {
+        return 0;
+    }
+    
+    void *secure_src = (void *)(upage->secure_page + ((uint64_t)user_src - upage->user_page));
+    memcpy(secure_dst, secure_src, size);
+    return 1;
+}
+
+int secure_copy_to_user(upage_ref_t *upage, void *user_dst, void *secure_src, size_t size) {    
+    /* Fail if the page doesn't match. */
+    if (get_page_for_address(user_dst) != upage->user_page) {
+        return 0;
+    }
+    
+    /* Fail if we go past the page boundary. */
+    if (size != 0 && get_page_for_address(user_dst + size - 1) != upage->user_page) {
+        return 0;
+    }
+
+    void *secure_dst = (void *)(upage->secure_page + ((uint64_t)user_dst - upage->user_page));
+    memcpy(secure_dst, secure_src, size);
+    return 1;
+}
\ No newline at end of file
diff --git a/exosphere/userpage.h b/exosphere/userpage.h
new file mode 100644
index 000000000..9f64b2fde
--- /dev/null
+++ b/exosphere/userpage.h
@@ -0,0 +1,22 @@
+#ifndef EXOSPHERE_USERPAGE_H
+#define EXOSPHERE_USERPAGE_H
+
+#include <stdint.h>
+
+#define SECURE_USER_PAGE_ADDR (0x1F01F4000ULL)
+
+typedef struct {
+    uint64_t user_page;
+    uint64_t secure_page;
+} upage_ref_t;
+
+int upage_init(upage_ref_t *user_page, void *user_address);
+
+void user_copy_to_secure(upage_ref_t *user_page, void *secure_dst, void *user_src, size_t size);
+void secure_copy_to_user(upage_ref_t *user_page, void *user_dst, void *secure_src, size_t size);
+
+static inline uint64_t get_page_for_address(void *address) {
+    return ((uint64_t)(address)) & 0xFFFFFFFFFFFFF000ULL;
+}
+
+#endif
\ No newline at end of file