1 files changed, 153 insertions, 0 deletions
diff --git a/kern/usermem.c b/kern/usermem.c
new file mode 100644
index 0000000..717cdbe
--- /dev/null
+++ b/kern/usermem.c
@@ -0,0 +1,153 @@
+/** @file usermem.c
+ *
+ *  @brief userspace r/w functions.
+ *
+ *  @author Hanjie Wu (hanjiew)
+ *  @bug No functional bugs
+ */
+
+#include <stdlib.h>
+#include <string.h>
+
+#include <common_kern.h>
+#include <x86/asm.h>
+
+#include <console.h>
+#include <mm.h>
+#include <paging.h>
+#include <sched.h>
+
+/**
+ * @brief try to read a byte from userspace
+ * @param addr address
+ * @param output output byte if successful
+ * @return 0 on success, jump to usermem_fail on failure
+ */
+int try_read(va_t addr, char* output);
+/**
+ * @brief try to write a byte to userspace
+ * @param addr address
+ * @param c byte to write
+ * @return 0 on success, jump to usermem_fail on failure
+ */
+int try_write(va_t addr, char c);
+
+/**
+ * @brief tell the calling function the r/w failed
+ * @return -1
+ */
+int usermem_fail();
+
+/**
+ * @brief setup fault handler before r/w
+ * @return old fault handler
+ */
+static reg_t usermem_setup() {
+    thread_t* current = get_current();
+    reg_t old_eip0 = current->eip0;
+    current->eip0 = (reg_t)usermem_fail;
+    return old_eip0;
+}
+
+/**
+ * @brief restore old fault handler
+ * @param old_eip0 old fault handler
+ */
+static void usermem_finish(reg_t old_eip0) {
+    get_current()->eip0 = old_eip0;
+}
+
+int copy_from_user(va_t addr, int size, void* buf) {
+    va_t end = addr + size;
+    if (addr < USER_MEM_START || end < addr || end >= DEFAULT_STACK_END) {
+        return -1;
+    }
+    reg_t old_eip0 = usermem_setup();
+    int i, result = 0;
+    for (i = 0; i < size; i++) {
+        if (try_read(addr + i, (char*)buf + i) != 0) {
+            result = -1;
+            break;
+        }
+    }
+    usermem_finish(old_eip0);
+    return result;
+}
+
+int copy_to_user(va_t addr, int size, void* buf) {
+    va_t end = addr + size;
+    if (addr < USER_MEM_START || end < addr || end >= DEFAULT_STACK_END) {
+        return -1;
+    }
+    reg_t old_eip0 = usermem_setup();
+    int i, result = 0;
+    for (i = 0; i < size; i++) {
+        if (try_write(addr + i, *((char*)buf + i)) != 0) {
+            result = -1;
+            break;
+        }
+    }
+    usermem_finish(old_eip0);
+    return result;
+}
+
+char* copy_string_from_user(va_t addr, int maxlen) {
+    if (addr < USER_MEM_START || addr >= DEFAULT_STACK_END) {
+        return NULL;
+    }
+    if (DEFAULT_STACK_END - addr < maxlen) {
+        maxlen = DEFAULT_STACK_END - addr;
+    }
+    reg_t old_eip0 = usermem_setup();
+    int len = 0, buflen = 3 * sizeof(int);
+    char* buf = malloc(buflen);
+    char c;
+    if (buf == NULL) {
+        goto read_string_finished;
+    }
+    while (1) {
+        if (len >= maxlen || try_read(addr + len, &c) != 0) {
+            free(buf);
+            buf = NULL;
+            break;
+        }
+
+        buf[len++] = c;
+        if (c == '\0') {
+            break;
+        }
+
+        if (len >= buflen) {
+            buflen <<= 1;
+            char* result = realloc(buf, buflen);
+            if (result == NULL) {
+                free(buf);
+                buf = NULL;
+                break;
+            }
+            buf = result;
+        }
+    }
+read_string_finished:
+    usermem_finish(old_eip0);
+    return buf;
+}
+
+int print_buf_from_user(va_t addr, int len) {
+    va_t end = addr + len;
+    if (addr < USER_MEM_START || end < addr || end >= DEFAULT_STACK_END) {
+        return -1;
+    }
+    reg_t old_eip0 = usermem_setup();
+    int i, result = 0;
+    char c;
+    for (i = 0; i < len; i++) {
+        if (try_read(addr + i, &c) != 0) {
+            result = -1;
+            break;
+        }
+        putbyte(c);
+    }
+    usermem_finish(old_eip0);
+    return result;
+}