[MIPS] Add seccomp bpf support

sandbox/linux/seccomp-bpf/trap.cc

Index: sandbox/linux/seccomp-bpf/trap.cc
diff --git a/sandbox/linux/seccomp-bpf/trap.cc b/sandbox/linux/seccomp-bpf/trap.cc
index f8b64c991b0f591c4d82bbb196e22acba7e96ece..8f710d033f1ea174f0487886ad3f0264a585804f 100644
--- a/sandbox/linux/seccomp-bpf/trap.cc
+++ b/sandbox/linux/seccomp-bpf/trap.cc
@@ -15,6 +15,7 @@
 #include "base/logging.h"
 #include "sandbox/linux/seccomp-bpf/codegen.h"
 #include "sandbox/linux/seccomp-bpf/die.h"
+#include "sandbox/linux/seccomp-bpf/kernel_return_value_helpers.h"
 #include "sandbox/linux/seccomp-bpf/syscall.h"
 
 // Android's signal.h doesn't define ucontext etc.
@@ -150,9 +151,20 @@ void Trap::SigSys(int nr, siginfo_t* info, void* void_context) {
   struct arch_sigsys sigsys;
   memcpy(&sigsys, &info->_sifields, sizeof(sigsys));
 
+  bool sigsys_nr_is_bad = true;
+#if defined(__mips__)
+  // When indirect syscall (syscall(__NR_foo, ...)) is made on Mips, the
+  // number in register SECCOMP_SYSCALL(ctx) is always __NR_syscall and the
+  // real number of a syscall (__NR_foo) is in SECCOMP_PARM1(ctx)
+  sigsys_nr_is_bad = sigsys.nr != static_cast<int>(SECCOMP_SYSCALL(ctx)) &&
+                     sigsys.nr != static_cast<int>(SECCOMP_PARM1(ctx));
+#else
+  sigsys_nr_is_bad = sigsys.nr != static_cast<int>(SECCOMP_SYSCALL(ctx));
+#endif
+
   // Some more sanity checks.
   if (sigsys.ip != reinterpret_cast<void*>(SECCOMP_IP(ctx)) ||
-      sigsys.nr != static_cast<int>(SECCOMP_SYSCALL(ctx)) ||
+      sigsys_nr_is_bad ||
       sigsys.arch != SECCOMP_ARCH) {
     // TODO(markus):
     // SANDBOX_DIE() can call LOG(FATAL). This is not normally async-signal
@@ -168,7 +180,7 @@ void Trap::SigSys(int nr, siginfo_t* info, void* void_context) {
     if (sigsys.nr == __NR_clone) {
       RAW_SANDBOX_DIE("Cannot call clone() from an UnsafeTrap() handler.");
     }
-    rc = SandboxSyscall(sigsys.nr,
+    rc = SandboxSyscall(SECCOMP_SYSCALL(ctx),
                         SECCOMP_PARM1(ctx),
                         SECCOMP_PARM2(ctx),
                         SECCOMP_PARM3(ctx),
@@ -185,7 +197,8 @@ void Trap::SigSys(int nr, siginfo_t* info, void* void_context) {
     // is what we are showing to TrapFnc callbacks that the system call
     // evaluator registered with the sandbox.
     struct arch_seccomp_data data = {
-        sigsys.nr, SECCOMP_ARCH, reinterpret_cast<uint64_t>(sigsys.ip),
+        static_cast<int>SECCOMP_SYSCALL(ctx), SECCOMP_ARCH,
+        reinterpret_cast<uint64_t>(sigsys.ip),
         {static_cast<uint64_t>(SECCOMP_PARM1(ctx)),
          static_cast<uint64_t>(SECCOMP_PARM2(ctx)),
          static_cast<uint64_t>(SECCOMP_PARM3(ctx)),
@@ -201,7 +214,7 @@ void Trap::SigSys(int nr, siginfo_t* info, void* void_context) {
   // Update the CPU register that stores the return code of the system call
   // that we just handled, and restore "errno" to the value that it had
   // before entering the signal handler.
-  SECCOMP_RESULT(ctx) = static_cast<greg_t>(rc);
+  PutValueInUcontext(static_cast<int>(rc), ctx);
   errno = old_errno;
 
   return;