Use PTRACE_SET_SYSCALL to override syscalls on ARM.

Unfortunately, this change also disables the test on ARM due to a bug
which prevents syscalls from being overriden on ARM (see
crbug.com/383977 for details).  This should fix ARM chrome tests, which
were broken in r276595.

BUG=383977

Review URL: https://codereview.chromium.org/331833002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@277089 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 34 insertions, 2 deletions

diff --git a/sandbox/linux/seccomp-bpf/sandbox_bpf_unittest.cc b/sandbox/linux/seccomp-bpf/sandbox_bpf_unittest.cc
index 9f02602..06ba209 100644
--- a/sandbox/linux/seccomp-bpf/sandbox_bpf_unittest.cc
+++ b/sandbox/linux/seccomp-bpf/sandbox_bpf_unittest.cc
@@ -1927,6 +1927,33 @@ BPF_TEST_C(SandboxBPF, PthreadBitMask, PthreadPolicyBitMask) {
 #define IS_SECCOMP_EVENT(status) ((status >> 16) == 7 || (status >> 16) == 8)
 #endif
 
+#if defined(__arm__)
+#ifndef PTRACE_SET_SYSCALL
+#define PTRACE_SET_SYSCALL 23
+#endif
+#endif
+
+// Changes the syscall to run for a child being sandboxed using seccomp-bpf with
+// PTRACE_O_TRACESECCOMP.  Should only be called when the child is stopped on
+// PTRACE_EVENT_SECCOMP.
+//
+// regs should contain the current set of registers of the child, obtained using
+// PTRACE_GETREGS.
+//
+// Depending on the architecture, this may modify regs, so the caller is
+// responsible for committing these changes using PTRACE_SETREGS.
+long SetSyscall(pid_t pid, regs_struct* regs, int syscall_number) {
+#if defined(__arm__)
+  // On ARM, the syscall is changed using PTRACE_SET_SYSCALL.  We cannot use the
+  // libc ptrace call as the request parameter is an enum, and
+  // PTRACE_SET_SYSCALL may not be in the enum.
+  return syscall(__NR_ptrace, PTRACE_SET_SYSCALL, pid, NULL, syscall_number);
+#endif
+
+  SECCOMP_PT_SYSCALL(*regs) = syscall_number;
+  return 0;
+}
+
 const uint16_t kTraceData = 0xcc;
 
 class TraceAllPolicy : public SandboxBPFPolicy {
@@ -1949,6 +1976,11 @@ SANDBOX_TEST(SandboxBPF, DISABLE_ON_TSAN(SeccompRetTrace)) {
     return;
   }
 
+#if defined(__arm__)
+  printf("This test is currently disabled on ARM due to a kernel bug.");
+  return;
+#endif
+
   pid_t pid = fork();
   BPF_ASSERT_NE(-1, pid);
   if (pid == 0) {
@@ -2005,7 +2037,7 @@ SANDBOX_TEST(SandboxBPF, DISABLE_ON_TSAN(SeccompRetTrace)) {
         // Skip writes to stdout, make it return kExpectedReturnValue.  Allow
         // writes to stderr so that BPF_ASSERT messages show up.
         if (SECCOMP_PT_PARM1(regs) == STDOUT_FILENO) {
-          SECCOMP_PT_SYSCALL(regs) = -1;
+          BPF_ASSERT_NE(-1, SetSyscall(pid, &regs, -1));
           SECCOMP_PT_RESULT(regs) = kExpectedReturnValue;
           BPF_ASSERT_NE(-1, ptrace(PTRACE_SETREGS, pid, NULL, &regs));
         }
@@ -2013,7 +2045,7 @@ SANDBOX_TEST(SandboxBPF, DISABLE_ON_TSAN(SeccompRetTrace)) {
 
       case __NR_kill:
         // Rewrite to exit(kExpectedReturnValue).
-        SECCOMP_PT_SYSCALL(regs) = __NR_exit;
+        BPF_ASSERT_NE(-1, SetSyscall(pid, &regs, __NR_exit));
         SECCOMP_PT_PARM1(regs) = kExpectedReturnValue;
         BPF_ASSERT_NE(-1, ptrace(PTRACE_SETREGS, pid, NULL, &regs));
         break;