Add test for patching a system call instruction

tests/test_patching.cc

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <fcntl.h>
+
+#include "library.h"
+#include "sandbox.h"
+#include "test_runner.h"
+
+
+extern "C" int my_getpid(void);
+extern char my_getpid_end[];
+
+void patch_range(char *start, char *end) {
+  int maps_fd;
+  CHECK_SUCCEEDS((maps_fd = open("/proc/self/maps", O_RDONLY, 0)) >= 0);
+  playground::Maps maps(maps_fd);
+  playground::Library library;
+  library.setLibraryInfo(&maps);
+  char *extra_space = NULL;
+  int extra_size = 0;
+  char *page_start = (char *) ((uintptr_t) start & ~(getpagesize() - 1));

[Markus (顧孟勤), 2011/11/18 18:16:46]

You should probably round "end" up to the next page boundary. That way, you do
the right thing if your function straddles a page boundary. And you also make
sure that mprotect always gets a "len" parameter that is a multiple of the page
size. I am actually surprised the kernel doesn't check this already.

+  CHECK_SUCCEEDS(mprotect(page_start, end - page_start,
+                          PROT_READ | PROT_WRITE | PROT_EXEC) == 0);
+  library.patchSystemCallsInRange(start, end, &extra_space, &extra_size);
+  CHECK_SUCCEEDS(close(maps_fd) == 0);
+}
+
+TEST(test_patching_syscall) {
+  int pid = getpid();
+  CHECK(my_getpid() == pid);
+  char *func = (char *) my_getpid;
+  char *func_end = my_getpid_end;
+  patch_range(func, func_end);
+#if defined(__x86_64__)
+  CHECK(func[0] == '\xe9'); // e9 XX XX XX XX   jmp X
+  CHECK(func[5] == '\x90'); // 90               nop
+  CHECK(func[6] == '\x90'); // 90               nop
+  CHECK(func[7] == '\xc3'); // c3               ret (unmodified)
+#elif defined(__i386__)
+  CHECK(func[0] == '\x68'); // 68 XX XX XX XX   push $X
+  CHECK(func[5] == '\xc3'); // c3               ret
+  CHECK(func[6] == '\x90'); // 90               nop
+  CHECK(func[7] == '\xc3'); // c3               ret (unmodified)
+#else
+# error Unsupported target platform
+#endif
+  StartSeccompSandbox();
+  CHECK(my_getpid() == pid);
+}