pk: only access user memory through explicit accessors

Enforced with sstatus.SUM.

1 files changed, 66 insertions, 0 deletions

diff --git a/pk/usermem.c b/pk/usermem.c
new file mode 100644
index 0000000..b65e515
--- /dev/null
+++ b/pk/usermem.c
@@ -0,0 +1,66 @@
+// See LICENSE for license details.
+
+#include "usermem.h"
+#include "mmap.h"
+#include <string.h>
+#include <stdint.h>
+
+void memset_user(void* dst, int ch, size_t n)
+{
+  if ((uintptr_t)dst + n < (uintptr_t)dst || !is_uva(dst + n - 1))
+    handle_page_fault((uintptr_t)dst, PROT_WRITE);
+
+  uintptr_t sstatus = set_csr(sstatus, SSTATUS_SUM);
+
+  memset(dst, ch, n);
+
+  write_csr(sstatus, sstatus);
+}
+
+void memcpy_to_user(void* dst, const void* src, size_t n)
+{
+  if ((uintptr_t)dst + n < (uintptr_t)dst || !is_uva(dst + n - 1))
+    handle_page_fault((uintptr_t)dst, PROT_WRITE);
+
+  uintptr_t sstatus = set_csr(sstatus, SSTATUS_SUM);
+
+  memcpy(dst, src, n);
+
+  write_csr(sstatus, sstatus);
+}
+
+void memcpy_from_user(void* dst, const void* src, size_t n)
+{
+  if ((uintptr_t)src + n < (uintptr_t)src || !is_uva(src + n - 1))
+    handle_page_fault((uintptr_t)src, PROT_READ);
+
+  uintptr_t sstatus = set_csr(sstatus, SSTATUS_SUM);
+
+  memcpy(dst, src, n);
+
+  write_csr(sstatus, sstatus);
+}
+
+bool strcpy_from_user(char* dst, const char* src, size_t n)
+{
+  uintptr_t sstatus = set_csr(sstatus, SSTATUS_SUM);
+
+  while (n > 0) {
+    if (!is_uva(src))
+      handle_page_fault((uintptr_t)src, PROT_READ);
+
+    char ch = *(volatile const char*)src;
+    *dst = ch;
+
+    if (ch == 0)
+      return true;
+
+    src++;
+    dst++;
+    n--;
+  }
+
+  write_csr(sstatus, sstatus);
+
+  return false;
+}