path: root/linux-sandbox-syscall-broker-use-struct-kernel_stat.patch

From 4b438323d68840453b5ef826c3997568e2e0e8c7 Mon Sep 17 00:00:00 2001
From: Matthew Denton <mpdenton@chromium.org>
Date: Mon, 19 Jul 2021 14:03:13 +0000
Subject: [PATCH] Reland "Reland "Linux sandbox syscall broker: use struct
 kernel_stat""

This reverts commit ff277a52ece0b216617d770f201ed66955fe70b9.

Reason for revert: reland

The fix included in the reland is that fstatat64() needs to be
allowed in the broker process's seccomp policy.

This CL also includes some extra tests that the kernel_stat structures
match the layout the kernel expects.

Bug: 1164975, 1199431
Test: trogdor Chromebook successfully boots and allows login.

Original change's description:
> Revert "Reland "Linux sandbox syscall broker: use struct kernel_stat""
>
> This reverts commit cffbc4432af79f720ae3c75dff380b853701bd64.
>
> Reason for revert: https://bugs.chromium.org/p/chromium/issues/detail?id=1199431
>
> Original change's description:
> > Reland "Linux sandbox syscall broker: use struct kernel_stat"
> >
> > This reverts commit 23030dc650cdfa22631f25bef937905f27f06a2c.
> >
> > Original change's description:
> > > Revert "Linux sandbox syscall broker: use struct kernel_stat"
> > >
> > > This reverts commit 784b0fcd8a3ca6bcd3acb9cfd624ec9cbbac2789.
> > >
> > > Reason for revert: Causing failure in
> > > Step "sandbox_linux_unittests" failing on builder "Linux ChromiumOS MSan Tests"
> > > See crbug.com/1198480
> > >
> > > Original change's description:
> > > > Linux sandbox syscall broker: use struct kernel_stat
> > > >
> > > > The struct stat used in libc is different (in size and field ordering)
> > > > from the structure assumed by the Linux kernel. So, when emulating
> > > > system calls, we need to use the struct definition the kernel expects.
> > > >
> > > > This CL adds linux_stat.h that includes definitions of the different
> > > > kernel structs.
> > > >
> > > > Change-Id: I53cad35c2251dff0f6b7ea77528cfa58ef3cab4a
> > > > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2780876
> > > > Commit-Queue: Matthew Denton <mpdenton@chromium.org>
> > > > Reviewed-by: Robert Sesek <rsesek@chromium.org>
> > > > Cr-Commit-Position: refs/heads/master@{#871767}
> > >
> > > Change-Id: Icbec38f2103c8424dec79ab1870b97c3e83f9361
> > > No-Presubmit: true
> > > No-Tree-Checks: true
> > > No-Try: true
> > > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2821812
> > > Auto-Submit: Victor Vianna <victorvianna@google.com>
> > > Owners-Override: Victor Vianna <victorvianna@google.com>
> > > Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> > > Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> > > Cr-Commit-Position: refs/heads/master@{#871882}
> >
> > Change-Id: I1f39bb5242961474def594ff7dbea52009f2cee4
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2824115
> > Auto-Submit: Matthew Denton <mpdenton@chromium.org>
> > Commit-Queue: Matthew Denton <mpdenton@chromium.org>
> > Reviewed-by: Robert Sesek <rsesek@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#872812}
>
> Fixed: 1199431
> Change-Id: Iebfc0c48201bf22ff9c54d8d5c8a43d26a880098
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2830459
> Auto-Submit: Kyle Horimoto <khorimoto@chromium.org>
> Commit-Queue: Matthew Denton <mpdenton@chromium.org>
> Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
> Reviewed-by: Matthew Denton <mpdenton@chromium.org>
> Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
> Owners-Override: Kinuko Yasuda <kinuko@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#873173}

Change-Id: Ibe6a485070f33489aaa157b51b908c2d23d174d7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2848936
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Commit-Queue: Matthew Denton <mpdenton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#902981}
---
 sandbox/linux/BUILD.gn                        |   1 +
 .../seccomp_broker_process_unittest.cc        |  40 +++-
 sandbox/linux/seccomp-bpf-helpers/DEPS        |   1 -
 ...scall_parameters_restrictions_unittests.cc |   4 -
 sandbox/linux/services/syscall_wrappers.cc    |  50 ++++-
 sandbox/linux/services/syscall_wrappers.h     |  15 ++
 .../services/syscall_wrappers_unittest.cc     | 129 +++++++++++-
 sandbox/linux/syscall_broker/DEPS             |   3 +-
 sandbox/linux/syscall_broker/broker_client.cc |   4 +-
 sandbox/linux/syscall_broker/broker_client.h  |   4 +-
 sandbox/linux/syscall_broker/broker_host.cc   |  23 ++-
 .../syscall_broker/broker_process_unittest.cc |  74 +++----
 .../remote_syscall_arg_handler_unittest.cc    |  36 ++--
 .../syscall_broker/syscall_dispatcher.cc      |  67 ++++---
 .../linux/syscall_broker/syscall_dispatcher.h |  27 ++-
 sandbox/linux/system_headers/linux_stat.h     | 188 ++++++++++++++++++
 sandbox/linux/system_headers/linux_time.h     |  26 +++
 sandbox/linux/tests/test_utils.cc             |  15 ++
 sandbox/linux/tests/test_utils.h              |   2 +
 .../policy/linux/bpf_broker_policy_linux.cc   |   4 +-
 20 files changed, 595 insertions(+), 118 deletions(-)
 create mode 100644 sandbox/linux/system_headers/linux_stat.h

diff --git a/sandbox/linux/BUILD.gn b/sandbox/linux/BUILD.gn
index 2f778dd0bc..ccbbc91716 100644
--- a/sandbox/linux/BUILD.gn
+++ b/sandbox/linux/BUILD.gn
@@ -443,6 +443,7 @@ source_set("sandbox_services_headers") {
     "system_headers/linux_ptrace.h",
     "system_headers/linux_seccomp.h",
     "system_headers/linux_signal.h",
+    "system_headers/linux_stat.h",
     "system_headers/linux_syscalls.h",
     "system_headers/linux_time.h",
     "system_headers/linux_ucontext.h",
diff --git a/sandbox/linux/integration_tests/seccomp_broker_process_unittest.cc b/sandbox/linux/integration_tests/seccomp_broker_process_unittest.cc
index 9da9c68911..8a941983b1 100644
--- a/sandbox/linux/integration_tests/seccomp_broker_process_unittest.cc
+++ b/sandbox/linux/integration_tests/seccomp_broker_process_unittest.cc
@@ -34,6 +34,7 @@
 #include "sandbox/linux/syscall_broker/broker_file_permission.h"
 #include "sandbox/linux/syscall_broker/broker_process.h"
 #include "sandbox/linux/system_headers/linux_seccomp.h"
+#include "sandbox/linux/system_headers/linux_stat.h"
 #include "sandbox/linux/system_headers/linux_syscalls.h"
 #include "sandbox/linux/tests/scoped_temporary_file.h"
 #include "sandbox/linux/tests/test_utils.h"
@@ -202,6 +203,26 @@ namespace {
 // not accept this as a valid error number. E.g. bionic accepts up to 255, glibc
 // and musl up to 4096.
 const int kFakeErrnoSentinel = 254;
+
+void ConvertKernelStatToLibcStat(default_stat_struct& in_stat,
+                                 struct stat& out_stat) {
+  out_stat.st_dev = in_stat.st_dev;
+  out_stat.st_ino = in_stat.st_ino;
+  out_stat.st_mode = in_stat.st_mode;
+  out_stat.st_nlink = in_stat.st_nlink;
+  out_stat.st_uid = in_stat.st_uid;
+  out_stat.st_gid = in_stat.st_gid;
+  out_stat.st_rdev = in_stat.st_rdev;
+  out_stat.st_size = in_stat.st_size;
+  out_stat.st_blksize = in_stat.st_blksize;
+  out_stat.st_blocks = in_stat.st_blocks;
+  out_stat.st_atim.tv_sec = in_stat.st_atime_;
+  out_stat.st_atim.tv_nsec = in_stat.st_atime_nsec_;
+  out_stat.st_mtim.tv_sec = in_stat.st_mtime_;
+  out_stat.st_mtim.tv_nsec = in_stat.st_mtime_nsec_;
+  out_stat.st_ctim.tv_sec = in_stat.st_ctime_;
+  out_stat.st_ctim.tv_nsec = in_stat.st_ctime_nsec_;
+}
 }  // namespace
 
 // There are a variety of ways to make syscalls in a sandboxed process. One is
@@ -217,6 +238,10 @@ class Syscaller {
 
   virtual int Open(const char* filepath, int flags) = 0;
   virtual int Access(const char* filepath, int mode) = 0;
+  // NOTE: we use struct stat instead of default_stat_struct, to make the libc
+  // syscaller simpler. Copying from default_stat_struct (the structure returned
+  // from a stat sycall) to struct stat (the structure exposed by a libc to its
+  // users) is simpler than going in the opposite direction.
   virtual int Stat(const char* filepath,
                    bool follow_links,
                    struct stat* statbuf) = 0;
@@ -243,8 +268,12 @@ class IPCSyscaller : public Syscaller {
   int Stat(const char* filepath,
            bool follow_links,
            struct stat* statbuf) override {
-    return broker_->GetBrokerClientSignalBased()->Stat(filepath, follow_links,
-                                                       statbuf);
+    default_stat_struct buf;
+    int ret = broker_->GetBrokerClientSignalBased()->DefaultStatForTesting(
+        filepath, follow_links, &buf);
+    if (ret >= 0)
+      ConvertKernelStatToLibcStat(buf, *statbuf);
+    return ret;
   }
 
   int Rename(const char* oldpath, const char* newpath) override {
@@ -300,10 +329,13 @@ class DirectSyscaller : public Syscaller {
   int Stat(const char* filepath,
            bool follow_links,
            struct stat* statbuf) override {
-    int ret = follow_links ? syscall(__NR_stat, filepath, statbuf)
-                           : syscall(__NR_lstat, filepath, statbuf);
+    struct kernel_stat buf;
+    int ret = syscall(__NR_newfstatat, AT_FDCWD, filepath, &buf,
+                      follow_links ? 0 : AT_SYMLINK_NOFOLLOW);
     if (ret < 0)
       return -errno;
+
+    ConvertKernelStatToLibcStat(buf, *statbuf);
     return ret;
   }
 
diff --git a/sandbox/linux/seccomp-bpf-helpers/DEPS b/sandbox/linux/seccomp-bpf-helpers/DEPS
index 4419fd1da3..95d1bb6cbb 100644
--- a/sandbox/linux/seccomp-bpf-helpers/DEPS
+++ b/sandbox/linux/seccomp-bpf-helpers/DEPS
@@ -3,5 +3,4 @@ include_rules = [
   "+sandbox/linux/seccomp-bpf",
   "+sandbox/linux/services",
   "+sandbox/linux/system_headers",
-  "+third_party/lss/linux_syscall_support.h",
 ]
diff --git a/sandbox/linux/seccomp-bpf-helpers/syscall_parameters_restrictions_unittests.cc b/sandbox/linux/seccomp-bpf-helpers/syscall_parameters_restrictions_unittests.cc
index 903e702eab..76c393032c 100644
--- a/sandbox/linux/seccomp-bpf-helpers/syscall_parameters_restrictions_unittests.cc
+++ b/sandbox/linux/seccomp-bpf-helpers/syscall_parameters_restrictions_unittests.cc
@@ -37,10 +37,6 @@
 #include "sandbox/linux/system_headers/linux_time.h"
 #include "sandbox/linux/tests/unit_tests.h"
 
-#if !defined(OS_ANDROID)
-#include "third_party/lss/linux_syscall_support.h"  // for MAKE_PROCESS_CPUCLOCK
-#endif
-
 namespace sandbox {
 
 namespace {
diff --git a/sandbox/linux/services/syscall_wrappers.cc b/sandbox/linux/services/syscall_wrappers.cc
index fcfd2aa129..3bec18a14e 100644
--- a/sandbox/linux/services/syscall_wrappers.cc
+++ b/sandbox/linux/services/syscall_wrappers.cc
@@ -4,6 +4,7 @@
 
 #include "sandbox/linux/services/syscall_wrappers.h"
 
+#include <fcntl.h>
 #include <pthread.h>
 #include <sched.h>
 #include <setjmp.h>
@@ -14,11 +15,13 @@
 #include <unistd.h>
 #include <cstring>
 
+#include "base/check.h"
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "build/build_config.h"
 #include "sandbox/linux/system_headers/capability.h"
 #include "sandbox/linux/system_headers/linux_signal.h"
+#include "sandbox/linux/system_headers/linux_stat.h"
 #include "sandbox/linux/system_headers/linux_syscalls.h"
 
 namespace sandbox {
@@ -217,7 +220,7 @@ asm(
 #undef STR
 #undef XSTR
 
-#endif
+#endif  // defined(ARCH_CPU_X86_FAMILY)
 
 int sys_sigaction(int signum,
                   const struct sigaction* act,
@@ -241,7 +244,7 @@ int sys_sigaction(int signum,
 #error "Unsupported architecture."
 #endif
     }
-#endif
+#endif  // defined(ARCH_CPU_X86_FAMILY)
   }
 
   LinuxSigAction linux_oldact = {};
@@ -259,6 +262,47 @@ int sys_sigaction(int signum,
   return result;
 }
 
-#endif  // defined(MEMORY_SANITIZER)
+#endif  // !defined(OS_NACL_NONSFI)
+
+int sys_stat(const char* path, struct kernel_stat* stat_buf) {
+  int res;
+#if !defined(__NR_stat)
+  res = syscall(__NR_newfstatat, AT_FDCWD, path, stat_buf, 0);
+#else
+  res = syscall(__NR_stat, path, stat_buf);
+#endif
+  if (res == 0)
+    MSAN_UNPOISON(stat_buf, sizeof(*stat_buf));
+  return res;
+}
+
+int sys_lstat(const char* path, struct kernel_stat* stat_buf) {
+  int res;
+#if !defined(__NR_lstat)
+  res = syscall(__NR_newfstatat, AT_FDCWD, path, stat_buf, AT_SYMLINK_NOFOLLOW);
+#else
+  res = syscall(__NR_lstat, path, stat_buf);
+#endif
+  if (res == 0)
+    MSAN_UNPOISON(stat_buf, sizeof(*stat_buf));
+  return res;
+}
+
+int sys_fstatat64(int dirfd,
+                  const char* pathname,
+                  struct kernel_stat64* stat_buf,
+                  int flags) {
+#if defined(__NR_fstatat64)
+  int res = syscall(__NR_fstatat64, dirfd, pathname, stat_buf, flags);
+  if (res == 0)
+    MSAN_UNPOISON(stat_buf, sizeof(*stat_buf));
+  return res;
+#else  // defined(__NR_fstatat64)
+  // We should not reach here on 64-bit systems, as the *stat*64() are only
+  // necessary on 32-bit.
+  RAW_CHECK(false);
+  return -ENOSYS;
+#endif
+}
 
 }  // namespace sandbox
diff --git a/sandbox/linux/services/syscall_wrappers.h b/sandbox/linux/services/syscall_wrappers.h
index 1975bfbd88..b55340e4a2 100644
--- a/sandbox/linux/services/syscall_wrappers.h
+++ b/sandbox/linux/services/syscall_wrappers.h
@@ -17,6 +17,8 @@ struct sock_fprog;
 struct rlimit64;
 struct cap_hdr;
 struct cap_data;
+struct kernel_stat;
+struct kernel_stat64;
 
 namespace sandbox {
 
@@ -84,6 +86,19 @@ SANDBOX_EXPORT int sys_sigaction(int signum,
                                  const struct sigaction* act,
                                  struct sigaction* oldact);
 
+// Some architectures do not have stat() and lstat() syscalls. In that case,
+// these wrappers will use newfstatat(), which is available on all other
+// architectures, with the same capabilities as stat() and lstat().
+SANDBOX_EXPORT int sys_stat(const char* path, struct kernel_stat* stat_buf);
+SANDBOX_EXPORT int sys_lstat(const char* path, struct kernel_stat* stat_buf);
+
+// Takes care of unpoisoning |stat_buf| for MSAN. Check-fails if fstatat64() is
+// not a supported syscall on the current platform.
+SANDBOX_EXPORT int sys_fstatat64(int dirfd,
+                                 const char* pathname,
+                                 struct kernel_stat64* stat_buf,
+                                 int flags);
+
 }  // namespace sandbox
 
 #endif  // SANDBOX_LINUX_SERVICES_SYSCALL_WRAPPERS_H_
diff --git a/sandbox/linux/services/syscall_wrappers_unittest.cc b/sandbox/linux/services/syscall_wrappers_unittest.cc
index 32820f60a8..64b9cea80f 100644
--- a/sandbox/linux/services/syscall_wrappers_unittest.cc
+++ b/sandbox/linux/services/syscall_wrappers_unittest.cc
@@ -5,15 +5,19 @@
 #include "sandbox/linux/services/syscall_wrappers.h"
 
 #include <stdint.h>
+#include <string.h>
 #include <sys/syscall.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
-#include <cstring>
 
+#include "base/logging.h"
+#include "base/memory/page_size.h"
 #include "base/posix/eintr_wrapper.h"
 #include "build/build_config.h"
 #include "sandbox/linux/system_headers/linux_signal.h"
+#include "sandbox/linux/system_headers/linux_stat.h"
+#include "sandbox/linux/tests/scoped_temporary_file.h"
 #include "sandbox/linux/tests/test_utils.h"
 #include "sandbox/linux/tests/unit_tests.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -93,6 +97,129 @@ TEST(SyscallWrappers, LinuxSigSet) {
             linux_sigset);
 }
 
+TEST(SyscallWrappers, Stat) {
+  // Create a file to stat, with 12 bytes of data.
+  ScopedTemporaryFile tmp_file;
+  EXPECT_EQ(12, write(tmp_file.fd(), "blahblahblah", 12));
+
+  // To test we have the correct stat structures for each kernel/platform, we
+  // will right-align them on a page, with a guard page after.
+  char* two_pages = static_cast<char*>(TestUtils::MapPagesOrDie(2));
+  TestUtils::MprotectLastPageOrDie(two_pages, 2);
+  char* page1_end = two_pages + base::GetPageSize();
+
+  // First, check that calling stat with |stat_buf| pointing to the last byte on
+  // a page causes EFAULT.
+  int res = sys_stat(tmp_file.full_file_name(),
+                     reinterpret_cast<struct kernel_stat*>(page1_end - 1));
+  ASSERT_EQ(res, -1);
+  ASSERT_EQ(errno, EFAULT);
+
+  // Now, check that we have the correctly sized stat structure.
+  struct kernel_stat* sb = reinterpret_cast<struct kernel_stat*>(
+      page1_end - sizeof(struct kernel_stat));
+  // Memset to c's so we can check the kernel zero'd the padding...
+  memset(sb, 'c', sizeof(struct kernel_stat));
+  res = sys_stat(tmp_file.full_file_name(), sb);
+  ASSERT_EQ(res, 0);
+
+  // Following fields may never be consistent but should be non-zero.
+  // Don't trust the platform to define fields with any particular sign.
+  EXPECT_NE(0u, static_cast<unsigned int>(sb->st_dev));
+  EXPECT_NE(0u, static_cast<unsigned int>(sb->st_ino));
+  EXPECT_NE(0u, static_cast<unsigned int>(sb->st_mode));
+  EXPECT_NE(0u, static_cast<unsigned int>(sb->st_blksize));
+  EXPECT_NE(0u, static_cast<unsigned int>(sb->st_blocks));
+
+// We are the ones that made the file.
+// Note: normally gid and uid overflow on backwards-compatible 32-bit systems
+// and we end up with dummy uids and gids in place here.
+#if defined(ARCH_CPU_64_BITS)
+  EXPECT_EQ(geteuid(), sb->st_uid);
+  EXPECT_EQ(getegid(), sb->st_gid);
+#endif
+
+  // Wrote 12 bytes above which should fit in one block.
+  EXPECT_EQ(12u, sb->st_size);
+
+  // Can't go backwards in time, 1500000000 was some time ago.
+  EXPECT_LT(1500000000u, static_cast<unsigned int>(sb->st_atime_));
+  EXPECT_LT(1500000000u, static_cast<unsigned int>(sb->st_mtime_));
+  EXPECT_LT(1500000000u, static_cast<unsigned int>(sb->st_ctime_));
+
+  // Checking the padding for good measure.
+#if defined(__x86_64__)
+  EXPECT_EQ(0u, sb->__pad0);
+  EXPECT_EQ(0u, sb->__unused4[0]);
+  EXPECT_EQ(0u, sb->__unused4[1]);
+  EXPECT_EQ(0u, sb->__unused4[2]);
+#elif defined(__aarch64__)
+  EXPECT_EQ(0u, sb->__pad1);
+  EXPECT_EQ(0, sb->__pad2);
+  EXPECT_EQ(0u, sb->__unused4);
+  EXPECT_EQ(0u, sb->__unused5);
+#endif
+}
+
+TEST(SyscallWrappers, LStat) {
+  // Create a file to stat, with 12 bytes of data.
+  ScopedTemporaryFile tmp_file;
+  EXPECT_EQ(12, write(tmp_file.fd(), "blahblahblah", 12));
+
+  // Also create a symlink.
+  std::string symlink_name;
+  {
+    ScopedTemporaryFile tmp_file2;
+    symlink_name = tmp_file2.full_file_name();
+  }
+  int rc = symlink(tmp_file.full_file_name(), symlink_name.c_str());
+  if (rc != 0) {
+    PLOG(ERROR) << "Couldn't symlink " << symlink_name << " to target "
+                << tmp_file.full_file_name();
+    GTEST_FAIL();
+  }
+
+  struct kernel_stat lstat_info;
+  rc = sys_lstat(symlink_name.c_str(), &lstat_info);
+  if (rc < 0 && errno == EOVERFLOW) {
+    GTEST_SKIP();
+  }
+  if (rc != 0) {
+    PLOG(ERROR) << "Couldn't sys_lstat " << symlink_name;
+    GTEST_FAIL();
+  }
+
+  struct kernel_stat stat_info;
+  rc = sys_stat(symlink_name.c_str(), &stat_info);
+  if (rc < 0 && errno == EOVERFLOW) {
+    GTEST_SKIP();
+  }
+  if (rc != 0) {
+    PLOG(ERROR) << "Couldn't sys_stat " << symlink_name;
+    GTEST_FAIL();
+  }
+
+  struct kernel_stat tmp_file_stat_info;
+  rc = sys_stat(tmp_file.full_file_name(), &tmp_file_stat_info);
+  if (rc < 0 && errno == EOVERFLOW) {
+    GTEST_SKIP();
+  }
+  if (rc != 0) {
+    PLOG(ERROR) << "Couldn't sys_stat " << tmp_file.full_file_name();
+    GTEST_FAIL();
+  }
+
+  // lstat should produce information about a symlink.
+  ASSERT_TRUE(S_ISLNK(lstat_info.st_mode));
+
+  // stat-ing symlink_name and tmp_file should produce the same inode.
+  ASSERT_EQ(stat_info.st_ino, tmp_file_stat_info.st_ino);
+
+  // lstat-ing symlink_name should give a different inode than stat-ing
+  // symlink_name.
+  ASSERT_NE(stat_info.st_ino, lstat_info.st_ino);
+}
+
 }  // namespace
 
 }  // namespace sandbox
diff --git a/sandbox/linux/syscall_broker/DEPS b/sandbox/linux/syscall_broker/DEPS
index c477f7d363..149c463b06 100644
--- a/sandbox/linux/syscall_broker/DEPS
+++ b/sandbox/linux/syscall_broker/DEPS
@@ -1,4 +1,5 @@
 include_rules = [
-  "+sandbox/linux/system_headers",
   "+sandbox/linux/bpf_dsl",
+  "+sandbox/linux/services",
+  "+sandbox/linux/system_headers",
 ]
diff --git a/sandbox/linux/syscall_broker/broker_client.cc b/sandbox/linux/syscall_broker/broker_client.cc
index 6b1b5be433..e24f659fcf 100644
--- a/sandbox/linux/syscall_broker/broker_client.cc
+++ b/sandbox/linux/syscall_broker/broker_client.cc
@@ -166,7 +166,7 @@ int BrokerClient::Rmdir(const char* path) const {
 
 int BrokerClient::Stat(const char* pathname,
                        bool follow_links,
-                       struct stat* sb) const {
+                       struct kernel_stat* sb) const {
   if (!pathname || !sb)
     return -EFAULT;
 
@@ -181,7 +181,7 @@ int BrokerClient::Stat(const char* pathname,
 
 int BrokerClient::Stat64(const char* pathname,
                          bool follow_links,
-                         struct stat64* sb) const {
+                         struct kernel_stat64* sb) const {
   if (!pathname || !sb)
     return -EFAULT;
 
diff --git a/sandbox/linux/syscall_broker/broker_client.h b/sandbox/linux/syscall_broker/broker_client.h
index 05e14c83f2..26ca78101c 100644
--- a/sandbox/linux/syscall_broker/broker_client.h
+++ b/sandbox/linux/syscall_broker/broker_client.h
@@ -61,10 +61,10 @@ class SANDBOX_EXPORT BrokerClient : public SyscallDispatcher {
   int Rmdir(const char* path) const override;
   int Stat(const char* pathname,
            bool follow_links,
-           struct stat* sb) const override;
+           struct kernel_stat* sb) const override;
   int Stat64(const char* pathname,
              bool follow_links,
-             struct stat64* sb) const override;
+             struct kernel_stat64* sb) const override;
   int Unlink(const char* unlink) const override;
 
  private:
diff --git a/sandbox/linux/syscall_broker/broker_host.cc b/sandbox/linux/syscall_broker/broker_host.cc
index 1cd03a18df..1cdc01a888 100644
--- a/sandbox/linux/syscall_broker/broker_host.cc
+++ b/sandbox/linux/syscall_broker/broker_host.cc
@@ -20,9 +20,11 @@
 #include "base/files/scoped_file.h"
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
+#include "sandbox/linux/services/syscall_wrappers.h"
 #include "sandbox/linux/syscall_broker/broker_command.h"
 #include "sandbox/linux/syscall_broker/broker_permission_list.h"
 #include "sandbox/linux/syscall_broker/broker_simple_message.h"
+#include "sandbox/linux/system_headers/linux_stat.h"
 #include "sandbox/linux/system_headers/linux_syscalls.h"
 
 namespace sandbox {
@@ -193,10 +195,12 @@ void StatFileForIPC(const BrokerCommandSet& allowed_command_set,
     RAW_CHECK(reply->AddIntToMessage(-permission_list.denied_errno()));
     return;
   }
+
   if (command_type == COMMAND_STAT) {
-    struct stat sb;
-    int sts =
-        follow_links ? stat(file_to_access, &sb) : lstat(file_to_access, &sb);
+    struct kernel_stat sb;
+
+    int sts = follow_links ? sandbox::sys_stat(file_to_access, &sb)
+                           : sandbox::sys_lstat(file_to_access, &sb);
     if (sts < 0) {
       RAW_CHECK(reply->AddIntToMessage(-errno));
       return;
@@ -205,10 +209,12 @@ void StatFileForIPC(const BrokerCommandSet& allowed_command_set,
     RAW_CHECK(
         reply->AddDataToMessage(reinterpret_cast<char*>(&sb), sizeof(sb)));
   } else {
+#if defined(__NR_fstatat64)
     DCHECK(command_type == COMMAND_STAT64);
-    struct stat64 sb;
-    int sts = follow_links ? stat64(file_to_access, &sb)
-                           : lstat64(file_to_access, &sb);
+    struct kernel_stat64 sb;
+
+    int sts = sandbox::sys_fstatat64(AT_FDCWD, file_to_access, &sb,
+                                     follow_links ? 0 : AT_SYMLINK_NOFOLLOW);
     if (sts < 0) {
       RAW_CHECK(reply->AddIntToMessage(-errno));
       return;
@@ -216,6 +222,11 @@ void StatFileForIPC(const BrokerCommandSet& allowed_command_set,
     RAW_CHECK(reply->AddIntToMessage(0));
     RAW_CHECK(
         reply->AddDataToMessage(reinterpret_cast<char*>(&sb), sizeof(sb)));
+#else  // defined(__NR_fstatat64)
+    // We should not reach here on 64-bit systems, as the *stat*64() are only
+    // necessary on 32-bit.
+    RAW_CHECK(false);
+#endif
   }
 }
 
diff --git a/sandbox/linux/syscall_broker/broker_process_unittest.cc b/sandbox/linux/syscall_broker/broker_process_unittest.cc
index 55ba6bccb2..c65f25a78a 100644
--- a/sandbox/linux/syscall_broker/broker_process_unittest.cc
+++ b/sandbox/linux/syscall_broker/broker_process_unittest.cc
@@ -811,7 +811,7 @@ void TestStatHelper(bool fast_check_in_client, bool follow_links) {
   const char* bad_leading_path5 = "/mbogo/fictitioux";
   const char* bad_leading_path6 = "/mbogo/fictitiousa";
 
-  struct stat sb;
+  default_stat_struct sb;
 
   {
     // Actual file with permissions to see file but command not allowed.
@@ -824,7 +824,7 @@ void TestStatHelper(bool fast_check_in_client, bool follow_links) {
 
     memset(&sb, 0, sizeof(sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   tempfile_name, follow_links, &sb));
   }
 
@@ -840,7 +840,7 @@ void TestStatHelper(bool fast_check_in_client, bool follow_links) {
 
     memset(&sb, 0, sizeof(sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   nonesuch_name, follow_links, &sb));
   }
   {
@@ -852,7 +852,7 @@ void TestStatHelper(bool fast_check_in_client, bool follow_links) {
 
     memset(&sb, 0, sizeof(sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   tempfile_name, follow_links, &sb));
   }
   {
@@ -864,38 +864,39 @@ void TestStatHelper(bool fast_check_in_client, bool follow_links) {
     ASSERT_TRUE(open_broker.Init(base::BindOnce(&NoOpCallback)));
 
     memset(&sb, 0, sizeof(sb));
-    EXPECT_EQ(-ENOENT, open_broker.GetBrokerClientSignalBased()->Stat(
-                           nonesuch_name, follow_links, &sb));
+    EXPECT_EQ(-ENOENT,
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
+                  nonesuch_name, follow_links, &sb));
 
     // Gets denied all the way back to root since no create permission.
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   leading_path1, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   leading_path2, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   leading_path3, follow_links, &sb));
 
     // Not fooled by substrings.
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path1, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path2, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path3, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path4, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path5, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path6, follow_links, &sb));
   }
   {
@@ -907,37 +908,41 @@ void TestStatHelper(bool fast_check_in_client, bool follow_links) {
     ASSERT_TRUE(open_broker.Init(base::BindOnce(&NoOpCallback)));
 
     memset(&sb, 0, sizeof(sb));
-    EXPECT_EQ(-ENOENT, open_broker.GetBrokerClientSignalBased()->Stat(
-                           nonesuch_name, follow_links, &sb));
+    EXPECT_EQ(-ENOENT,
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
+                  nonesuch_name, follow_links, &sb));
 
     // Gets ENOENT all the way back to root since it has create permission.
-    EXPECT_EQ(-ENOENT, open_broker.GetBrokerClientSignalBased()->Stat(
-                           leading_path1, follow_links, &sb));
-    EXPECT_EQ(-ENOENT, open_broker.GetBrokerClientSignalBased()->Stat(
-                           leading_path2, follow_links, &sb));
+    EXPECT_EQ(-ENOENT,
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
+                  leading_path1, follow_links, &sb));
+    EXPECT_EQ(-ENOENT,
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
+                  leading_path2, follow_links, &sb));
 
     // But can always get the root.
-    EXPECT_EQ(0, open_broker.GetBrokerClientSignalBased()->Stat(
-                     leading_path3, follow_links, &sb));
+    EXPECT_EQ(0,
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
+                  leading_path3, follow_links, &sb));
 
     // Not fooled by substrings.
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path1, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path2, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path3, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path4, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path5, follow_links, &sb));
     EXPECT_EQ(-kFakeErrnoSentinel,
-              open_broker.GetBrokerClientSignalBased()->Stat(
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
                   bad_leading_path6, follow_links, &sb));
   }
   {
@@ -949,8 +954,9 @@ void TestStatHelper(bool fast_check_in_client, bool follow_links) {
     ASSERT_TRUE(open_broker.Init(base::BindOnce(&NoOpCallback)));
 
     memset(&sb, 0, sizeof(sb));
-    EXPECT_EQ(0, open_broker.GetBrokerClientSignalBased()->Stat(
-                     tempfile_name, follow_links, &sb));
+    EXPECT_EQ(0,
+              open_broker.GetBrokerClientSignalBased()->DefaultStatForTesting(
+                  tempfile_name, follow_links, &sb));
 
     // Following fields may never be consistent but should be non-zero.
     // Don't trust the platform to define fields with any particular sign.
@@ -968,9 +974,9 @@ void TestStatHelper(bool fast_check_in_client, bool follow_links) {
     EXPECT_EQ(12, sb.st_size);
 
     // Can't go backwards in time, 1500000000 was some time ago.
-    EXPECT_LT(1500000000u, static_cast<unsigned int>(sb.st_atime));
-    EXPECT_LT(1500000000u, static_cast<unsigned int>(sb.st_mtime));
-    EXPECT_LT(1500000000u, static_cast<unsigned int>(sb.st_ctime));
+    EXPECT_LT(1500000000u, static_cast<unsigned int>(sb.st_atime_));
+    EXPECT_LT(1500000000u, static_cast<unsigned int>(sb.st_mtime_));
+    EXPECT_LT(1500000000u, static_cast<unsigned int>(sb.st_ctime_));
   }
 }
 
diff --git a/sandbox/linux/syscall_broker/remote_syscall_arg_handler_unittest.cc b/sandbox/linux/syscall_broker/remote_syscall_arg_handler_unittest.cc
index fffa9bb708..f517a9867c 100644
--- a/sandbox/linux/syscall_broker/remote_syscall_arg_handler_unittest.cc
+++ b/sandbox/linux/syscall_broker/remote_syscall_arg_handler_unittest.cc
@@ -16,6 +16,7 @@
 #include "base/memory/page_size.h"
 #include "base/posix/unix_domain_socket.h"
 #include "base/test/bind.h"
+#include "sandbox/linux/tests/test_utils.h"
 #include "sandbox/linux/tests/unit_tests.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -52,19 +53,6 @@ void VerifyCorrectString(std::string str, size_t size) {
   }
 }
 
-void* MapPagesOrDie(size_t num_pages) {
-  void* addr = mmap(nullptr, num_pages * base::GetPageSize(),
-                    PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-  PCHECK(addr);
-  return addr;
-}
-
-void MprotectLastPageOrDie(char* addr, size_t num_pages) {
-  size_t last_page_offset = (num_pages - 1) * base::GetPageSize();
-  PCHECK(mprotect(addr + last_page_offset, base::GetPageSize(), PROT_NONE) >=
-         0);
-}
-
 pid_t ForkWaitingChild(base::OnceCallback<void(int)>
                            after_parent_signals_callback = base::DoNothing(),
                        base::ScopedFD* parent_sync_fd = nullptr) {
@@ -105,13 +93,13 @@ void ReadTest(const ReadTestConfig& test_config) {
   size_t total_pages = (test_config.start_at + test_config.total_size +
                         base::GetPageSize() - 1) /
                        base::GetPageSize();
-  char* mmap_addr = static_cast<char*>(MapPagesOrDie(total_pages));
+  char* mmap_addr = static_cast<char*>(TestUtils::MapPagesOrDie(total_pages));
   char* addr = mmap_addr + test_config.start_at;
   FillBufferWithPath(addr, test_config.total_size,
                      test_config.include_null_byte);
 
   if (test_config.last_page_inaccessible)
-    MprotectLastPageOrDie(mmap_addr, total_pages);
+    TestUtils::MprotectLastPageOrDie(mmap_addr, total_pages);
 
   pid_t pid = ForkWaitingChild();
   munmap(mmap_addr, base::GetPageSize() * total_pages);
@@ -212,7 +200,7 @@ SANDBOX_TEST(BrokerRemoteSyscallArgHandler, ReadChunkPlus1EndingOnePastPage) {
 }
 
 SANDBOX_TEST(BrokerRemoteSyscallArgHandler, ReadChildExited) {
-  void* addr = MapPagesOrDie(1);
+  void* addr = TestUtils::MapPagesOrDie(1);
   FillBufferWithPath(static_cast<char*>(addr), strlen(kPathPart) + 1, true);
 
   base::ScopedFD parent_sync, child_sync;
@@ -240,10 +228,10 @@ SANDBOX_TEST(BrokerRemoteSyscallArgHandler, ReadChildExited) {
 }
 
 SANDBOX_TEST(BrokerRemoteSyscallArgHandler, BasicWrite) {
-  void* read_from = MapPagesOrDie(1);
+  void* read_from = TestUtils::MapPagesOrDie(1);
   const size_t write_size = base::GetPageSize();
   FillBufferWithPath(static_cast<char*>(read_from), write_size, false);
-  char* write_to = static_cast<char*>(MapPagesOrDie(1));
+  char* write_to = static_cast<char*>(TestUtils::MapPagesOrDie(1));
   base::ScopedFD parent_signal_fd;
   const std::vector<int> empty_fd_vec;
 
@@ -278,8 +266,8 @@ SANDBOX_TEST(BrokerRemoteSyscallArgHandler, BasicWrite) {
 }
 
 SANDBOX_TEST(BrokerRemoteSyscallArgHandler, WriteToInvalidAddress) {
-  char* write_to = static_cast<char*>(MapPagesOrDie(1));
-  MprotectLastPageOrDie(write_to, 1);
+  char* write_to = static_cast<char*>(TestUtils::MapPagesOrDie(1));
+  TestUtils::MprotectLastPageOrDie(write_to, 1);
   base::ScopedFD parent_signal_fd;
   const std::vector<int> empty_fd_vec;
 
@@ -295,11 +283,11 @@ SANDBOX_TEST(BrokerRemoteSyscallArgHandler, WriteToInvalidAddress) {
 }
 
 SANDBOX_TEST(BrokerRemoteSyscallArgHandler, WritePartiallyToInvalidAddress) {
-  char* read_from = static_cast<char*>(MapPagesOrDie(2));
+  char* read_from = static_cast<char*>(TestUtils::MapPagesOrDie(2));
   const size_t write_size = base::GetPageSize();
   FillBufferWithPath(static_cast<char*>(read_from), write_size, false);
-  char* write_to = static_cast<char*>(MapPagesOrDie(2));
-  MprotectLastPageOrDie(write_to, 2);
+  char* write_to = static_cast<char*>(TestUtils::MapPagesOrDie(2));
+  TestUtils::MprotectLastPageOrDie(write_to, 2);
   write_to += base::GetPageSize() / 2;
   base::ScopedFD parent_signal_fd;
   const std::vector<int> empty_fd_vec;
@@ -314,7 +302,7 @@ SANDBOX_TEST(BrokerRemoteSyscallArgHandler, WritePartiallyToInvalidAddress) {
 }
 
 SANDBOX_TEST(BrokerRemoteSyscallArgHandler, WriteChildExited) {
-  char* addr = static_cast<char*>(MapPagesOrDie(1));
+  char* addr = static_cast<char*>(TestUtils::MapPagesOrDie(1));
   FillBufferWithPath(static_cast<char*>(addr), strlen(kPathPart) + 1, true);
 
   base::ScopedFD parent_sync, child_sync;
diff --git a/sandbox/linux/syscall_broker/syscall_dispatcher.cc b/sandbox/linux/syscall_broker/syscall_dispatcher.cc
index b9ee93c14a..8a42397ef8 100644
--- a/sandbox/linux/syscall_broker/syscall_dispatcher.cc
+++ b/sandbox/linux/syscall_broker/syscall_dispatcher.cc
@@ -19,8 +19,18 @@ namespace syscall_broker {
 #define BROKER_UNPOISON_STRING(x)
 #endif
 
+int SyscallDispatcher::DefaultStatForTesting(const char* pathname,
+                                             bool follow_links,
+                                             default_stat_struct* sb) {
+#if defined(__NR_fstatat64)
+  return Stat64(pathname, follow_links, sb);
+#elif defined(__NR_newfstatat)
+  return Stat(pathname, follow_links, sb);
+#endif
+}
+
 int SyscallDispatcher::PerformStatat(const arch_seccomp_data& args,
-                                     bool arch64) {
+                                     bool stat64) {
   if (static_cast<int>(args.args[0]) != AT_FDCWD)
     return -EPERM;
   // Only allow the AT_SYMLINK_NOFOLLOW flag which is used by some libc
@@ -30,13 +40,29 @@ int SyscallDispatcher::PerformStatat(const arch_seccomp_data& args,
 
   const bool follow_links =
       !(static_cast<int>(args.args[3]) & AT_SYMLINK_NOFOLLOW);
-  if (arch64) {
+  if (stat64) {
     return Stat64(reinterpret_cast<const char*>(args.args[1]), follow_links,
-                  reinterpret_cast<struct stat64*>(args.args[2]));
+                  reinterpret_cast<struct kernel_stat64*>(args.args[2]));
   }
 
   return Stat(reinterpret_cast<const char*>(args.args[1]), follow_links,
-              reinterpret_cast<struct stat*>(args.args[2]));
+              reinterpret_cast<struct kernel_stat*>(args.args[2]));
+}
+
+int SyscallDispatcher::PerformUnlinkat(const arch_seccomp_data& args) {
+  if (static_cast<int>(args.args[0]) != AT_FDCWD)
+    return -EPERM;
+
+  int flags = static_cast<int>(args.args[2]);
+
+  if (flags == AT_REMOVEDIR) {
+    return Rmdir(reinterpret_cast<const char*>(args.args[1]));
+  }
+
+  if (flags != 0)
+    return -EPERM;
+
+  return Unlink(reinterpret_cast<const char*>(args.args[1]));
 }
 
 int SyscallDispatcher::DispatchSyscall(const arch_seccomp_data& args) {
@@ -127,59 +153,42 @@ int SyscallDispatcher::DispatchSyscall(const arch_seccomp_data& args) {
 #if defined(__NR_stat)
     case __NR_stat:
       return Stat(reinterpret_cast<const char*>(args.args[0]), true,
-                  reinterpret_cast<struct stat*>(args.args[1]));
+                  reinterpret_cast<struct kernel_stat*>(args.args[1]));
 #endif
 #if defined(__NR_stat64)
     case __NR_stat64:
       return Stat64(reinterpret_cast<const char*>(args.args[0]), true,
-                    reinterpret_cast<struct stat64*>(args.args[1]));
+                    reinterpret_cast<struct kernel_stat64*>(args.args[1]));
 #endif
 #if defined(__NR_lstat)
     case __NR_lstat:
       // See https://crbug.com/847096
       BROKER_UNPOISON_STRING(reinterpret_cast<const char*>(args.args[0]));
       return Stat(reinterpret_cast<const char*>(args.args[0]), false,
-                  reinterpret_cast<struct stat*>(args.args[1]));
+                  reinterpret_cast<struct kernel_stat*>(args.args[1]));
 #endif
 #if defined(__NR_lstat64)
     case __NR_lstat64:
       // See https://crbug.com/847096
       BROKER_UNPOISON_STRING(reinterpret_cast<const char*>(args.args[0]));
       return Stat64(reinterpret_cast<const char*>(args.args[0]), false,
-                    reinterpret_cast<struct stat64*>(args.args[1]));
-#endif
-#if defined(__NR_fstatat)
-    case __NR_fstatat:
-      return PerformStatat(args, /*arch64=*/false);
+                    reinterpret_cast<struct kernel_stat64*>(args.args[1]));
 #endif
 #if defined(__NR_fstatat64)
     case __NR_fstatat64:
-      return PerformStatat(args, /*arch64=*/true);
+      return PerformStatat(args, /*stat64=*/true);
 #endif
 #if defined(__NR_newfstatat)
     case __NR_newfstatat:
-      return PerformStatat(args, /*arch64=*/false);
+      return PerformStatat(args, /*stat64=*/false);
 #endif
 #if defined(__NR_unlink)
     case __NR_unlink:
       return Unlink(reinterpret_cast<const char*>(args.args[0]));
 #endif
 #if defined(__NR_unlinkat)
-    case __NR_unlinkat: {
-      if (static_cast<int>(args.args[0]) != AT_FDCWD)
-        return -EPERM;
-
-      int flags = static_cast<int>(args.args[2]);
-
-      if (flags == AT_REMOVEDIR) {
-        return Rmdir(reinterpret_cast<const char*>(args.args[1]));
-      }
-
-      if (flags != 0)
-        return -EPERM;
-
-      return Unlink(reinterpret_cast<const char*>(args.args[1]));
-    }
+    case __NR_unlinkat:
+      return PerformUnlinkat(args);
 #endif  // defined(__NR_unlinkat)
     default:
       RAW_CHECK(false);
diff --git a/sandbox/linux/syscall_broker/syscall_dispatcher.h b/sandbox/linux/syscall_broker/syscall_dispatcher.h
index d8b8874ad9..1d6653caf3 100644
--- a/sandbox/linux/syscall_broker/syscall_dispatcher.h
+++ b/sandbox/linux/syscall_broker/syscall_dispatcher.h
@@ -9,13 +9,15 @@
 #include <cstddef>
 
 #include "sandbox/linux/system_headers/linux_seccomp.h"
+#include "sandbox/linux/system_headers/linux_stat.h"
+#include "sandbox/sandbox_export.h"
 
 namespace sandbox {
 namespace syscall_broker {
 
 // An abstract class that defines all the system calls we perform for the
 // sandboxed process.
-class SyscallDispatcher {
+class SANDBOX_EXPORT SyscallDispatcher {
  public:
   // Emulates access()/faccessat().
   // X_OK will always return an error in practice since the broker process
@@ -40,19 +42,34 @@ class SyscallDispatcher {
   virtual int Rmdir(const char* path) const = 0;
 
   // Emulates stat()/stat64()/lstat()/lstat64()/fstatat()/newfstatat().
+  // Stat64 is only available on 32-bit systems.
   virtual int Stat(const char* pathname,
                    bool follow_links,
-                   struct stat* sb) const = 0;
+                   struct kernel_stat* sb) const = 0;
   virtual int Stat64(const char* pathname,
                      bool follow_links,
-                     struct stat64* sb) const = 0;
+                     struct kernel_stat64* sb) const = 0;
 
   // Emulates unlink()/unlinkat().
   virtual int Unlink(const char* unlink) const = 0;
 
+  // Different architectures use a different syscall from the stat family by
+  // default in glibc. E.g. 32-bit systems use *stat*64() and fill out struct
+  // kernel_stat64, whereas 64-bit systems use *stat*() and fill out struct
+  // kernel_stat. Some tests want to call the SyscallDispatcher directly, and
+  // should be using the default stat in order to test against glibc.
+  int DefaultStatForTesting(const char* pathname,
+                            bool follow_links,
+                            default_stat_struct* sb);
+
   // Validates the args passed to a *statat*() syscall and performs the syscall
-  // using Stat() or Stat64().
-  int PerformStatat(const arch_seccomp_data& args, bool arch64);
+  // using Stat(), or on 32-bit systems it uses Stat64() for the *statat64()
+  // syscalls.
+  int PerformStatat(const arch_seccomp_data& args, bool stat64);
+
+  // Validates the args passed to an unlinkat() syscall and performs the syscall
+  // using either Unlink() or Rmdir().
+  int PerformUnlinkat(const arch_seccomp_data& args);
 
   // Reads the syscall number and arguments, imposes some policy (e.g. the *at()
   // system calls must only allow AT_FDCWD as the first argument), and
diff --git a/sandbox/linux/system_headers/linux_stat.h b/sandbox/linux/system_headers/linux_stat.h
new file mode 100644
index 0000000000..35788eb22a
--- /dev/null
+++ b/sandbox/linux/system_headers/linux_stat.h
@@ -0,0 +1,188 @@
+// Copyright 2021 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.
+
+#ifndef SANDBOX_LINUX_SYSTEM_HEADERS_LINUX_STAT_H_
+#define SANDBOX_LINUX_SYSTEM_HEADERS_LINUX_STAT_H_
+
+#include <stdint.h>
+
+#include "build/build_config.h"
+#include "sandbox/linux/system_headers/linux_syscalls.h"
+
+#if defined(ARCH_CPU_MIPS_FAMILY)
+#if defined(ARCH_CPU_64_BITS)
+struct kernel_stat {
+#else
+struct kernel_stat64 {
+#endif
+  unsigned st_dev;
+  unsigned __pad0[3];
+  unsigned long long st_ino;
+  unsigned st_mode;
+  unsigned st_nlink;
+  unsigned st_uid;
+  unsigned st_gid;
+  unsigned st_rdev;
+  unsigned __pad1[3];
+  long long st_size;
+  unsigned st_atime_;
+  unsigned st_atime_nsec_;
+  unsigned st_mtime_;
+  unsigned st_mtime_nsec_;
+  unsigned st_ctime_;
+  unsigned st_ctime_nsec_;
+  unsigned st_blksize;
+  unsigned __pad2;
+  unsigned long long st_blocks;
+};
+#else
+struct kernel_stat64 {
+  unsigned long long st_dev;
+  unsigned char __pad0[4];
+  unsigned __st_ino;
+  unsigned st_mode;
+  unsigned st_nlink;
+  unsigned st_uid;
+  unsigned st_gid;
+  unsigned long long st_rdev;
+  unsigned char __pad3[4];
+  long long st_size;
+  unsigned st_blksize;
+  unsigned long long st_blocks;
+  unsigned st_atime_;
+  unsigned st_atime_nsec_;
+  unsigned st_mtime_;
+  unsigned st_mtime_nsec_;
+  unsigned st_ctime_;
+  unsigned st_ctime_nsec_;
+  unsigned long long st_ino;
+};
+#endif
+
+#if defined(__i386__) || defined(__ARM_ARCH_3__) || defined(__ARM_EABI__)
+struct kernel_stat {
+  /* The kernel headers suggest that st_dev and st_rdev should be 32bit
+   * quantities encoding 12bit major and 20bit minor numbers in an interleaved
+   * format. In reality, we do not see useful data in the top bits. So,
+   * we'll leave the padding in here, until we find a better solution.
+   */
+  unsigned short st_dev;
+  short pad1;
+  unsigned st_ino;
+  unsigned short st_mode;
+  unsigned short st_nlink;
+  unsigned short st_uid;
+  unsigned short st_gid;
+  unsigned short st_rdev;
+  short pad2;
+  unsigned st_size;
+  unsigned st_blksize;
+  unsigned st_blocks;
+  unsigned st_atime_;
+  unsigned st_atime_nsec_;
+  unsigned st_mtime_;
+  unsigned st_mtime_nsec_;
+  unsigned st_ctime_;
+  unsigned st_ctime_nsec_;
+  unsigned __unused4;
+  unsigned __unused5;
+};
+#elif defined(__x86_64__)
+struct kernel_stat {
+  uint64_t st_dev;
+  uint64_t st_ino;
+  uint64_t st_nlink;
+  unsigned st_mode;
+  unsigned st_uid;
+  unsigned st_gid;
+  unsigned __pad0;
+  uint64_t st_rdev;
+  int64_t st_size;
+  int64_t st_blksize;
+  int64_t st_blocks;
+  uint64_t st_atime_;
+  uint64_t st_atime_nsec_;
+  uint64_t st_mtime_;
+  uint64_t st_mtime_nsec_;
+  uint64_t st_ctime_;
+  uint64_t st_ctime_nsec_;
+  int64_t __unused4[3];
+};
+#elif (defined(ARCH_CPU_MIPS_FAMILY) && defined(ARCH_CPU_32_BITS))
+struct kernel_stat {
+  unsigned st_dev;
+  int st_pad1[3];
+  unsigned st_ino;
+  unsigned st_mode;
+  unsigned st_nlink;
+  unsigned st_uid;
+  unsigned st_gid;
+  unsigned st_rdev;
+  int st_pad2[2];
+  long st_size;
+  int st_pad3;
+  long st_atime_;
+  long st_atime_nsec_;
+  long st_mtime_;
+  long st_mtime_nsec_;
+  long st_ctime_;
+  long st_ctime_nsec_;
+  int st_blksize;
+  int st_blocks;
+  int st_pad4[14];
+};
+#elif defined(__aarch64__)
+struct kernel_stat {
+  unsigned long st_dev;
+  unsigned long st_ino;
+  unsigned int st_mode;
+  unsigned int st_nlink;
+  unsigned int st_uid;
+  unsigned int st_gid;
+  unsigned long st_rdev;
+  unsigned long __pad1;
+  long st_size;
+  int st_blksize;
+  int __pad2;
+  long st_blocks;
+  long st_atime_;
+  unsigned long st_atime_nsec_;
+  long st_mtime_;
+  unsigned long st_mtime_nsec_;
+  long st_ctime_;
+  unsigned long st_ctime_nsec_;
+  unsigned int __unused4;
+  unsigned int __unused5;
+};
+#endif
+
+// On 32-bit systems, we default to the 64-bit stat struct like libc
+// implementations do. Otherwise we default to the normal stat struct which is
+// already 64-bit.
+// These defines make it easy to call the right syscall to fill out a 64-bit
+// stat struct, which is the default in libc implementations but requires
+// different syscall names on 32 and 64-bit platforms.
+#if defined(__NR_fstatat64)
+
+namespace sandbox {
+using default_stat_struct = struct kernel_stat64;
+}  // namespace sandbox
+
+#define __NR_fstatat_default __NR_fstatat64
+#define __NR_fstat_default __NR_fstat64
+
+#elif defined(__NR_newfstatat)
+
+namespace sandbox {
+using default_stat_struct = struct kernel_stat;
+}  // namespace sandbox
+
+#define __NR_fstatat_default __NR_newfstatat
+#define __NR_fstat_default __NR_fstat
+
+#else
+#error "one of fstatat64 and newfstatat must be defined"
+#endif
+
+#endif  // SANDBOX_LINUX_SYSTEM_HEADERS_LINUX_STAT_H_
diff --git a/sandbox/linux/system_headers/linux_time.h b/sandbox/linux/system_headers/linux_time.h
index 780f24dddd..f18c806611 100644
--- a/sandbox/linux/system_headers/linux_time.h
+++ b/sandbox/linux/system_headers/linux_time.h
@@ -11,6 +11,32 @@
 #define CPUCLOCK_CLOCK_MASK 3
 #endif
 
+#if !defined(CPUCLOCK_PROF)
+#define CPUCLOCK_PROF 0
+#endif
+
+#if !defined(CPUCLOCK_VIRT)
+#define CPUCLOCK_VIRT 1
+#endif
+
+#if !defined(CPUCLOCK_SCHED)
+#define CPUCLOCK_SCHED 2
+#endif
+
+#if !defined(CPUCLOCK_PERTHREAD_MASK)
+#define CPUCLOCK_PERTHREAD_MASK 4
+#endif
+
+#if !defined(MAKE_PROCESS_CPUCLOCK)
+#define MAKE_PROCESS_CPUCLOCK(pid, clock) \
+  ((int)(~(unsigned)(pid) << 3) | (int)(clock))
+#endif
+
+#if !defined(MAKE_THREAD_CPUCLOCK)
+#define MAKE_THREAD_CPUCLOCK(tid, clock) \
+  ((int)(~(unsigned)(tid) << 3) | (int)((clock) | CPUCLOCK_PERTHREAD_MASK))
+#endif
+
 #if !defined(CLOCKFD)
 #define CLOCKFD 3
 #endif
diff --git a/sandbox/linux/tests/test_utils.cc b/sandbox/linux/tests/test_utils.cc
index 847c20b20c..cf6041a4b4 100644
--- a/sandbox/linux/tests/test_utils.cc
+++ b/sandbox/linux/tests/test_utils.cc
@@ -5,12 +5,14 @@
 #include "sandbox/linux/tests/test_utils.h"
 
 #include <errno.h>
+#include <sys/mman.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
 #include "base/check_op.h"
+#include "base/memory/page_size.h"
 #include "base/posix/eintr_wrapper.h"
 
 namespace sandbox {
@@ -39,4 +41,17 @@ void TestUtils::HandlePostForkReturn(pid_t pid) {
   }
 }
 
+void* TestUtils::MapPagesOrDie(size_t num_pages) {
+  void* addr = mmap(nullptr, num_pages * base::GetPageSize(),
+                    PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  PCHECK(addr);
+  return addr;
+}
+
+void TestUtils::MprotectLastPageOrDie(char* addr, size_t num_pages) {
+  size_t last_page_offset = (num_pages - 1) * base::GetPageSize();
+  PCHECK(mprotect(addr + last_page_offset, base::GetPageSize(), PROT_NONE) >=
+         0);
+}
+
 }  // namespace sandbox
diff --git a/sandbox/linux/tests/test_utils.h b/sandbox/linux/tests/test_utils.h
index 7cf9749fe4..43b028b1e3 100644
--- a/sandbox/linux/tests/test_utils.h
+++ b/sandbox/linux/tests/test_utils.h
@@ -19,6 +19,8 @@ class TestUtils {
   // makes sure that if fork() succeeded the child exits
   // and the parent waits for it.
   static void HandlePostForkReturn(pid_t pid);
+  static void* MapPagesOrDie(size_t num_pages);
+  static void MprotectLastPageOrDie(char* addr, size_t num_pages);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(TestUtils);
diff --git a/sandbox/policy/linux/bpf_broker_policy_linux.cc b/sandbox/policy/linux/bpf_broker_policy_linux.cc
index 2963bb9ca8..6dc8c0581b 100644
--- a/sandbox/policy/linux/bpf_broker_policy_linux.cc
+++ b/sandbox/policy/linux/bpf_broker_policy_linux.cc
@@ -93,8 +93,8 @@ ResultExpr BrokerProcessPolicy::EvaluateSyscall(int sysno) const {
         return Allow();
       break;
 #endif
-#if defined(__NR_fstatat)
-    case __NR_fstatat:
+#if defined(__NR_fstatat64)
+    case __NR_fstatat64:
       if (allowed_command_set_.test(syscall_broker::COMMAND_STAT))
         return Allow();
       break;