Revert of Set a new TLS when using CLONE_VM. (patchset #4 id:80001 of https://codereview.chromium.org/1248673004/)

Reason for revert:
This CL has broken ASan Linux (sandboxed) tests: basically every test from browser_tests, content_browsertests, interactive_ui_tests times out: http://build.chromium.org/p/chromium.memory/builders/Linux%20ASan%20Tests%20%28sandboxed%29/builds/15502

Original issue's description:
> Set a new TLS when using CLONE_VM.
>
> On some libcs, clone writes to the new child's TLS before returning, so
> we set a new TLS to avoid corrupting the parent process's TLS.
>
> On glibc, this caused an assertion failure inside of
> pthread_getattr_np(pthread_self(), &attr).
>
> BUG=512623
>
> Committed: https://crrev.com/d2516cf1c3843541c920a476315e2a6f10cb0f92
> Cr-Commit-Position: refs/heads/master@{#340025}

TBR=jln@chromium.org,rickyz@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=512623

Review URL: https://codereview.chromium.org/1256533002

Cr-Commit-Position: refs/heads/master@{#340069}

2 files changed, 3 insertions, 46 deletions

diff --git a/sandbox/linux/services/credentials.cc b/sandbox/linux/services/credentials.cc
index 014ae13..dc62f1b 100644
--- a/sandbox/linux/services/credentials.cc
+++ b/sandbox/linux/services/credentials.cc
@@ -54,9 +54,6 @@ bool GetRESIds(uid_t* resuid, gid_t* resgid) {
 const int kExitSuccess = 0;
 
 int ChrootToSelfFdinfo(void*) {
-  // This function can be run from a vforked child, so it should not write to
-  // any memory other than the stack or errno. Reads from TLS may be different
-  // from in the parent process.
   RAW_CHECK(sys_chroot("/proc/self/fdinfo/") == 0);
 
   // CWD is essentially an implicit file descriptor, so be careful to not
@@ -94,22 +91,9 @@ bool ChrootToSafeEmptyDir() {
 #error "Unsupported architecture"
 #endif
 
-  int clone_flags = CLONE_FS | LINUX_SIGCHLD;
-  void* tls = nullptr;
-#if defined(ARCH_CPU_X86_64) || defined(ARCH_CPU_ARM_FAMILY)
-  // Use CLONE_VM | CLONE_VFORK as an optimization to avoid copying page tables.
-  // Since clone writes to the new child's TLS before returning, we must set a
-  // new TLS to avoid corrupting the current process's TLS. On ARCH_CPU_X86,
-  // glibc performs syscalls by calling a function pointer in TLS, so we do not
-  // attempt this optimization.
-  clone_flags |= CLONE_VM | CLONE_VFORK | CLONE_SETTLS;
-
-  char tls_buf[PTHREAD_STACK_MIN] = {0};
-  tls = tls_buf;
-#endif
-
-  pid = clone(ChrootToSelfFdinfo, stack, clone_flags, nullptr, nullptr, tls,
-              nullptr);
+  pid = clone(ChrootToSelfFdinfo, stack,
+              CLONE_VM | CLONE_VFORK | CLONE_FS | LINUX_SIGCHLD, nullptr,
+              nullptr, nullptr, nullptr);
   PCHECK(pid != -1);
 
   int status = -1;
diff --git a/sandbox/linux/services/credentials_unittest.cc b/sandbox/linux/services/credentials_unittest.cc
index 39fd6a7..6b93c86 100644
--- a/sandbox/linux/services/credentials_unittest.cc
+++ b/sandbox/linux/services/credentials_unittest.cc
@@ -6,8 +6,6 @@
 
 #include <errno.h>
 #include <fcntl.h>
-#include <pthread.h>
-#include <signal.h>
 #include <stdio.h>
 #include <sys/capability.h>
 #include <sys/stat.h>
@@ -239,31 +237,6 @@ SANDBOX_TEST(Credentials, SetCapabilitiesMatchesLibCap2) {
   CHECK_EQ(0, cap_compare(expected_cap.get(), actual_cap.get()));
 }
 
-volatile sig_atomic_t signal_handler_called;
-void SignalHandler(int sig) {
-  signal_handler_called = 1;
-}
-
-// Disabled on ASAN because of crbug.com/451603.
-SANDBOX_TEST(Credentials, DISABLE_ON_ASAN(DropFileSystemAccessPreservesTLS)) {
-  // Probably missing kernel support.
-  if (!Credentials::MoveToNewUserNS()) return;
-  CHECK(Credentials::DropFileSystemAccess(ProcUtil::OpenProc().get()));
-
-  // In glibc, pthread_getattr_np makes an assertion about the cached PID/TID in
-  // TLS.
-  pthread_attr_t attr;
-  EXPECT_EQ(0, pthread_getattr_np(pthread_self(), &attr));
-
-  // raise also uses the cached TID in glibc.
-  struct sigaction action = {};
-  action.sa_handler = &SignalHandler;
-  PCHECK(sigaction(SIGUSR1, &action, nullptr) == 0);
-
-  PCHECK(raise(SIGUSR1) == 0);
-  CHECK_EQ(1, signal_handler_called);
-}
-
 }  // namespace.
 
 }  // namespace sandbox.