Add logic for patching calls to the x86-64 vsyscall page

tests/test_patching.cc

Index: tests/test_patching.cc
diff --git a/tests/test_patching.cc b/tests/test_patching.cc
index bb1babbc65a2a22856953edee5ef307066853dbf..448bdac30f047c45bf6e2c2489ff277dded1fe87 100644
--- a/tests/test_patching.cc
+++ b/tests/test_patching.cc
@@ -3,6 +3,8 @@
 // found in the LICENSE file.
 
 #include <fcntl.h>
+#include <stdlib.h>
+#include <sys/time.h>
 
 #include "library.h"
 #include "sandbox.h"
@@ -49,3 +51,82 @@ TEST(test_patching_syscall) {
   StartSeccompSandbox();
   CHECK(my_getpid() == pid);
 }
+
+#if defined(__x86_64__)
+
+// These test cases test patching calls to the vsyscall page, which is
+// present on x86-64 only.
+
+// The timer tests below could fail on a heavily loaded machine, but
+// we make a generous allowance for this.  They could also fail if the
+// clock is changed while the test is running.
+const int kMaxTime = 30; // Time in seconds
+
+extern "C" int my_vgettimeofday(struct timeval *tv, struct timezone *tz);
+extern char my_vgettimeofday_end[];
+
+extern "C" int my_vtime(time_t *time);
+extern char my_vtime_end[];
+
+extern "C" int my_vgetcpu(unsigned *cpu, unsigned *node, void *tcache);
+extern char my_vgetcpu_end[];
+
+void check_patching_vsyscall(char *func, char *func_end) {
+  patch_range(func, func_end);
+  CHECK(func[0] == '\x48');  // 48 83 ec 08      sub $8, %rsp (unmodified)
+  CHECK(func[1] == '\x83');
+  CHECK(func[2] == '\xec');
+  CHECK(func[3] == '\x08');
+  CHECK(func[4] == '\xe9');  // e9 XX XX XX XX   jmp X
+  CHECK(func[9] == '\x90');  // 90               nop
+  CHECK(func[10] == '\x90'); // 90               nop
+  CHECK(func[11] == '\x90'); // 90               nop
+  CHECK(func[12] == '\x90'); // 90               nop
+  CHECK(func[13] == '\x48'); // 48 83 c4 08      add $8, %rsp (unmodified)
+  CHECK(func[14] == '\x83');
+  CHECK(func[15] == '\xc4');
+  CHECK(func[16] == '\x08');
+  CHECK(func[17] == '\xc3'); // c3               ret (unmodified)
+}
+
+TEST(test_patching_vsyscall_gettimeofday) {
+  struct timeval time1;
+  struct timeval time2;
+  CHECK_SUCCEEDS(gettimeofday(&time1, NULL) == 0);
+  CHECK(my_vgettimeofday(&time2, NULL) == 0);
+  CHECK(time1.tv_sec <= time2.tv_sec && time2.tv_sec < time1.tv_sec + kMaxTime);
+
+  check_patching_vsyscall((char *) my_vgettimeofday, my_vgettimeofday_end);
+
+  StartSeccompSandbox();
+  CHECK(my_vgettimeofday(&time2, NULL) == 0);
+  CHECK(time1.tv_sec <= time2.tv_sec && time2.tv_sec < time1.tv_sec + kMaxTime);
+}
+
+TEST(test_patching_vsyscall_time) {
+  time_t time1;
+  time_t time2;
+  CHECK_SUCCEEDS((time1 = time(NULL)) != -1);
+  time2 = time(NULL);
+  CHECK(time1 <= time2 && time2 < time1 + kMaxTime);
+
+  check_patching_vsyscall((char *) my_vtime, my_vtime_end);
+
+  StartSeccompSandbox();
+  time2 = time(NULL);
+  CHECK(time1 <= time2 && time2 < time1 + kMaxTime);
+}
+
+TEST(test_patching_vsyscall_getcpu) {
+  CHECK(my_vgetcpu(NULL, NULL, NULL) == 0);
+
+  check_patching_vsyscall((char *) my_vgetcpu, my_vgetcpu_end);
+
+  StartSeccompSandbox();
+  // glibc's sched_getcpu() could still succeed if it goes via the
+  // vdso and just reads memory, but my_vgetcpu() is always redirected
+  // through the sandbox's handler and is rejected.
+  CHECK(my_vgetcpu(NULL, NULL, NULL) == -ENOSYS);
+}
+
+#endif