NaCl: enable a real seccomp-bpf sandbox.

chrome/nacl/nacl_sandbox_linux.cc

 // Copyright (c) 2013 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 "chrome/nacl/nacl_sandbox_linux.h"
 
 #include <signal.h>
 #include <sys/ptrace.h>
 
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
+#include "build/build_config.h"
 #include "content/public/common/sandbox_init.h"
 #include "sandbox/linux/seccomp-bpf/sandbox_bpf.h"
 #include "sandbox/linux/services/linux_syscalls.h"
 
 using playground2::ErrorCode;
 using playground2::Sandbox;
 
 namespace {
 
-// This policy does very little:
-// - Any invalid system call for the current architecture is handled by
-//   the baseline policy.
-// - ptrace() is denied.
-// - Anything else is allowed.
-// Note that the seccomp-bpf sandbox always prevents cross-architecture
-// system calls (on x86, long/compatibility/x32).
-// So even this trivial policy has a security benefit.
+inline bool IsPlatformX86() {
+#if defined(__x86_64__) || defined(__i386__)
+  return true;
+#else
+  return false;
+#endif
+}
+
+// On ARM and x86_64, System V shared memory calls have each their own system
+// call, while on i386 they are multiplexed.
+#if defined(__x86_64__) || defined(__arm__)
+bool IsSystemVSharedMemory(int sysno) {
+  switch (sysno) {
+    case __NR_shmat:
+    case __NR_shmctl:
+    case __NR_shmdt:
+    case __NR_shmget:
+      return true;
+    default:
+      return false;
+  }
+}
+#endif
+
+#if defined(__i386__)
+// Big system V multiplexing system call.
+bool IsSystemVIpc(int sysno) {
+  switch (sysno) {
+    case __NR_ipc:
+      return true;
+    default:
+      return false;
+  }
+}
+#endif
+
 ErrorCode NaClBpfSandboxPolicy(
-    playground2::Sandbox* sb, int sysnum, void* aux) {
+    playground2::Sandbox* sb, int sysno, void* aux) {
   const playground2::BpfSandboxPolicyCallback baseline_policy =
       content::GetBpfSandboxBaselinePolicy();
-  if (!playground2::Sandbox::IsValidSyscallNumber(sysnum)) {
-    return baseline_policy.Run(sb, sysnum, aux);
-  }
-  switch (sysnum) {
+  switch (sysno) {
+    // TODO(jln): NaCl's GDB debug stub uses the following socket system calls,
+    // see if it can be restricted a bit.
+#if defined(__x86_64__) || defined(__arm__)
+    // transport_common.cc needs this.
+    case __NR_accept:
+    case __NR_setsockopt:
+#elif defined(__i386__)
+    case __NR_socketcall:
+#endif
+    // trusted/service_runtime/linux/thread_suspension.c needs sigwait() and is
+    // used by NaCl's GDB debug stub.
+    case __NR_rt_sigtimedwait:
+#if defined(__i386__)
+    // Needed on i386 to set-up the custom segments.
+    case __NR_modify_ldt:
+#endif
+    // NaClAddrSpaceBeforeAlloc needs prlimit64.
+    case __NR_prlimit64:
+    // NaCl uses custom signal stacks.
+    case __NR_sigaltstack:
+    // Below is fairly similar to the policy for a Chromium renderer.
+    // TODO(jln): restrict clone(), ioctl() and prctl().
+    case __NR_ioctl:
+#if defined(__i386__) || defined(__x86_64__)
+    case __NR_getrlimit:
+#endif
+#if defined(__i386__) || defined(__arm__)
+    case __NR_ugetrlimit:
+#endif
+    case __NR_pread64:
+    case __NR_pwrite64:
+    case __NR_sched_get_priority_max:
+    case __NR_sched_get_priority_min:
+    case __NR_sched_getaffinity:
+    case __NR_sched_getparam:
+    case __NR_sched_getscheduler:
+    case __NR_sched_setscheduler:
+    case __NR_setpriority:
+    case __NR_sysinfo:
+    case __NR_uname:
+      return ErrorCode(ErrorCode::ERR_ALLOWED);
     case __NR_ptrace:
       return ErrorCode(EPERM);
     default:
-      return ErrorCode(ErrorCode::ERR_ALLOWED);
+      // TODO(jln): look into getting rid of System V shared memory:
+      // platform_qualify/linux/sysv_shm_and_mmap.c makes it a requirement, but
+      // it may not be needed in all cases. Chromium renderers don't need
+      // System V shared memory on Aura.
+#if defined(__x86_64__) || defined(__arm__)
+      if (IsSystemVSharedMemory(sysno))
+        return ErrorCode(ErrorCode::ERR_ALLOWED);
+#elif defined(__i386__)
+      if (IsSystemVIpc(sysno))
+        return ErrorCode(ErrorCode::ERR_ALLOWED);
+#endif
+      return baseline_policy.Run(sb, sysno, aux);
   }
   NOTREACHED();
   // GCC wants this.
   return ErrorCode(EPERM);
 }
 
 void RunSandboxSanityChecks() {
   errno = 0;
   // Make a ptrace request with an invalid PID.
   long ptrace_ret = ptrace(PTRACE_PEEKUSER, -1 /* pid */, NULL, NULL);
   CHECK_EQ(-1, ptrace_ret);
   // Without the sandbox on, this ptrace call would ESRCH instead.
   CHECK_EQ(EPERM, errno);
 }
 
 }  // namespace
 
 bool InitializeBpfSandbox() {
+  // TODO(jln): enable the sandbox on ARM as well.
+  if (!IsPlatformX86())
+    return false;
   bool sandbox_is_initialized =
       content::InitializeSandbox(NaClBpfSandboxPolicy);
   if (sandbox_is_initialized) {
     RunSandboxSanityChecks();
     // TODO(jln): Find a way to fix this.
     // The sandbox' SIGSYS handler trips NaCl, so we disable it.
     // If SIGSYS is triggered it'll now execute the default action
     // (CORE). This will make it hard to track down bugs and sandbox violations.
     CHECK(signal(SIGSYS, SIG_DFL) != SIG_ERR);
     return true;
   }
   return false;
 }