[MIPS] Add seccomp bpf support

sandbox/linux/seccomp-bpf/trap.cc

 // Copyright (c) 2012 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 "sandbox/linux/seccomp-bpf/trap.h"
 
 #include <errno.h>
 #include <signal.h>
 #include <string.h>
 #include <sys/prctl.h>
@@ skipping 141 matching lines @@
 
   // Some more sanity checks.
   if (sigsys.ip != reinterpret_cast<void*>(SECCOMP_IP(ctx)) ||
       sigsys.nr != static_cast<int>(SECCOMP_SYSCALL(ctx)) ||
       sigsys.arch != SECCOMP_ARCH) {
     // TODO(markus):
     // SANDBOX_DIE() can call LOG(FATAL). This is not normally async-signal
     // safe and can lead to bugs. We should eventually implement a different
     // logging and reporting mechanism that is safe to be called from
     // the sigSys() handler.
+#if defined (__mips__)

[jln (very slow on Chromium), 2014/05/02 20:42:04]

style: #if defined(), no space.

[nedeljko, 2014/05/07 15:40:05]

Done.

+    // When indirect syscall (syscall(__NR_foo, ...)) is made on Mips, number
+    // in register SECCOMP_SYSCALL(ctx) is always __NR_syscall and real
+    // number of a syscall (__NR_foo) is in SECCOMP_PARM1(ctx)
+    if (sigsys.nr != static_cast<int>(SECCOMP_PARM1(ctx)))
+      RAW_SANDBOX_DIE("Sanity checks are failing after receiving SIGSYS.");

[jln (very slow on Chromium), 2014/05/02 20:42:04]

I don't think this is correct. The code is no longer dying if "sigsys.arch !=
SECCOMP_ARCH" for instance.

do something like:

bool sigsys_nr_is_correct = false;
#if defined(__mips__)
sigsys_nr_is_correct = sigsys.nr == static_cast<int>(SECCOMP_PARM1(ctx)
#else
sigsys_nr == static_cast<int>(SECCOMP_SYSCALL(ctx))
#endif

And use this bool in the if()

[nedeljko, 2014/05/07 15:40:05]

Done.

+#else
     RAW_SANDBOX_DIE("Sanity checks are failing after receiving SIGSYS.");
+#endif
   }
 
   intptr_t rc;
   if (has_unsafe_traps_ && GetIsInSigHandler(ctx)) {
     errno = old_errno;
     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),
                         SECCOMP_PARM4(ctx),
                         SECCOMP_PARM5(ctx),
                         SECCOMP_PARM6(ctx));
   } else {
     const ErrorCode& err = trap_array_[info->si_errno - 1];
     if (!err.safe_) {
       SetIsInSigHandler();
     }
 
     // Copy the seccomp-specific data into a arch_seccomp_data structure. This
     // 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)),
          static_cast<uint64_t>(SECCOMP_PARM4(ctx)),
          static_cast<uint64_t>(SECCOMP_PARM5(ctx)),
          static_cast<uint64_t>(SECCOMP_PARM6(ctx))}};
 
     // Now call the TrapFnc callback associated with this particular instance
     // of SECCOMP_RET_TRAP.
     rc = err.fnc_(data, err.aux_);
   }
 
+#if defined(__mips__)
+  // Mips ABI states that on error a3 CPU register should be set to one
+  // and if there is no error, it should be zero.
+  // The other difference from Intel and Arm is in that on error kernel
+  // returns positive value of errno.
+  if(rc < 0) {
+    rc = -rc;

[jln (very slow on Chromium), 2014/05/02 20:42:04]

Let's use a wrapper for this (see comment in other files).

[nedeljko, 2014/05/07 15:40:05]

Done.

+    SECCOMP_PARM4(ctx) = 1;
+  } else {
+    SECCOMP_PARM4(ctx) = 0;
+  }
+#endif
   // 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);
   errno = old_errno;
 
   return;
 }
 
 bool Trap::TrapKey::operator<(const TrapKey& o) const {
@@ skipping 137 matching lines @@
   if (global_trap_ && id > 0 && id <= global_trap_->trap_array_size_) {
     return global_trap_->trap_array_[id - 1];
   } else {
     return ErrorCode();
   }
 }
 
 Trap* Trap::global_trap_;
 
 }  // namespace sandbox