Implement madvise(MADV_DONTFORK)

PiperOrigin-RevId: 254253777

3 files changed, 110 insertions, 11 deletions

diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index 7e3ad08a9..0618fea58 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -985,6 +985,7 @@ cc_binary(
         "//test/util:file_descriptor",
         "//test/util:logging",
         "//test/util:memory_util",
+        "//test/util:multiprocess_util",
         "//test/util:posix_error",
         "//test/util:temp_path",
         "//test/util:test_main",
diff --git a/test/syscalls/linux/madvise.cc b/test/syscalls/linux/madvise.cc
index f6ad4d18b..352fcc6c4 100644
--- a/test/syscalls/linux/madvise.cc
+++ b/test/syscalls/linux/madvise.cc
@@ -29,6 +29,7 @@
 #include "test/util/file_descriptor.h"
 #include "test/util/logging.h"
 #include "test/util/memory_util.h"
+#include "test/util/multiprocess_util.h"
 #include "test/util/posix_error.h"
 #include "test/util/temp_path.h"
 #include "test/util/test_util.h"
@@ -136,6 +137,114 @@ TEST(MadviseDontneedTest, IgnoresPermissions) {
   EXPECT_THAT(madvise(m.ptr(), m.len(), MADV_DONTNEED), SyscallSucceeds());
 }
 
+TEST(MadviseDontforkTest, AddressLength) {
+  auto m =
+      ASSERT_NO_ERRNO_AND_VALUE(MmapAnon(kPageSize, PROT_NONE, MAP_PRIVATE));
+  char *addr = static_cast<char *>(m.ptr());
+
+  // Address must be page aligned.
+  EXPECT_THAT(madvise(addr + 1, kPageSize, MADV_DONTFORK),
+              SyscallFailsWithErrno(EINVAL));
+
+  // Zero length madvise always succeeds.
+  EXPECT_THAT(madvise(addr, 0, MADV_DONTFORK), SyscallSucceeds());
+
+  // Length must not roll over after rounding up.
+  size_t badlen = std::numeric_limits<std::size_t>::max() - (kPageSize / 2);
+  EXPECT_THAT(madvise(0, badlen, MADV_DONTFORK), SyscallFailsWithErrno(EINVAL));
+
+  // Length need not be page aligned - it is implicitly rounded up.
+  EXPECT_THAT(madvise(addr, 1, MADV_DONTFORK), SyscallSucceeds());
+  EXPECT_THAT(madvise(addr, kPageSize, MADV_DONTFORK), SyscallSucceeds());
+}
+
+TEST(MadviseDontforkTest, DontforkShared) {
+  // Mmap two shared file-backed pages and MADV_DONTFORK the second page.
+  TempPath f = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFileWith(
+      /* parent = */ GetAbsoluteTestTmpdir(),
+      /* content = */ std::string(kPageSize * 2, 2), TempPath::kDefaultFileMode));
+  FileDescriptor fd = ASSERT_NO_ERRNO_AND_VALUE(Open(f.path(), O_RDWR));
+
+  Mapping m = ASSERT_NO_ERRNO_AND_VALUE(Mmap(
+      nullptr, kPageSize * 2, PROT_READ | PROT_WRITE, MAP_SHARED, fd.get(), 0));
+
+  const Mapping ms1 = Mapping(reinterpret_cast<void *>(m.addr()), kPageSize);
+  const Mapping ms2 =
+      Mapping(reinterpret_cast<void *>(m.addr() + kPageSize), kPageSize);
+  m.release();
+
+  ASSERT_THAT(madvise(ms2.ptr(), kPageSize, MADV_DONTFORK), SyscallSucceeds());
+
+  const auto rest = [&] {
+    // First page is mapped in child and modifications are visible to parent
+    // via the shared mapping.
+    TEST_CHECK(IsMapped(ms1.addr()));
+    ExpectAllMappingBytes(ms1, 2);
+    memset(ms1.ptr(), 1, kPageSize);
+    ExpectAllMappingBytes(ms1, 1);
+
+    // Second page must not be mapped in child.
+    TEST_CHECK(!IsMapped(ms2.addr()));
+  };
+
+  EXPECT_THAT(InForkedProcess(rest), IsPosixErrorOkAndHolds(0));
+
+  ExpectAllMappingBytes(ms1, 1);  // page contents modified by child.
+  ExpectAllMappingBytes(ms2, 2);  // page contents unchanged.
+}
+
+TEST(MadviseDontforkTest, DontforkAnonPrivate) {
+  // Mmap three anonymous pages and MADV_DONTFORK the middle page.
+  Mapping m = ASSERT_NO_ERRNO_AND_VALUE(
+      MmapAnon(kPageSize * 3, PROT_READ | PROT_WRITE, MAP_PRIVATE));
+  const Mapping mp1 = Mapping(reinterpret_cast<void *>(m.addr()), kPageSize);
+  const Mapping mp2 =
+      Mapping(reinterpret_cast<void *>(m.addr() + kPageSize), kPageSize);
+  const Mapping mp3 =
+      Mapping(reinterpret_cast<void *>(m.addr() + 2 * kPageSize), kPageSize);
+  m.release();
+
+  ASSERT_THAT(madvise(mp2.ptr(), kPageSize, MADV_DONTFORK), SyscallSucceeds());
+
+  // Verify that all pages are zeroed and memset the first, second and third
+  // pages to 1, 2, and 3 respectively.
+  ExpectAllMappingBytes(mp1, 0);
+  memset(mp1.ptr(), 1, kPageSize);
+
+  ExpectAllMappingBytes(mp2, 0);
+  memset(mp2.ptr(), 2, kPageSize);
+
+  ExpectAllMappingBytes(mp3, 0);
+  memset(mp3.ptr(), 3, kPageSize);
+
+  const auto rest = [&] {
+    // Verify first page is mapped, verify its contents and then modify the
+    // page. The mapping is private so the modifications are not visible to
+    // the parent.
+    TEST_CHECK(IsMapped(mp1.addr()));
+    ExpectAllMappingBytes(mp1, 1);
+    memset(mp1.ptr(), 11, kPageSize);
+    ExpectAllMappingBytes(mp1, 11);
+
+    // Verify second page is not mapped.
+    TEST_CHECK(!IsMapped(mp2.addr()));
+
+    // Verify third page is mapped, verify its contents and then modify the
+    // page. The mapping is private so the modifications are not visible to
+    // the parent.
+    TEST_CHECK(IsMapped(mp3.addr()));
+    ExpectAllMappingBytes(mp3, 3);
+    memset(mp3.ptr(), 13, kPageSize);
+    ExpectAllMappingBytes(mp3, 13);
+  };
+  EXPECT_THAT(InForkedProcess(rest), IsPosixErrorOkAndHolds(0));
+
+  // The fork and COW by child should not affect the parent mappings.
+  ExpectAllMappingBytes(mp1, 1);
+  ExpectAllMappingBytes(mp2, 2);
+  ExpectAllMappingBytes(mp3, 3);
+}
+
 }  // namespace
 
 }  // namespace testing
diff --git a/test/syscalls/linux/mremap.cc b/test/syscalls/linux/mremap.cc
index 7298d4ca8..64e435cb7 100644
--- a/test/syscalls/linux/mremap.cc
+++ b/test/syscalls/linux/mremap.cc
@@ -46,17 +46,6 @@ PosixErrorOr<void*> Mremap(void* old_address, size_t old_size, size_t new_size,
   return rv;
 }
 
-// Returns true if the page containing addr is mapped.
-bool IsMapped(uintptr_t addr) {
-  int const rv = msync(reinterpret_cast<void*>(addr & ~(kPageSize - 1)),
-                       kPageSize, MS_ASYNC);
-  if (rv == 0) {
-    return true;
-  }
-  TEST_PCHECK_MSG(errno == ENOMEM, "msync failed with unexpected errno");
-  return false;
-}
-
 // Fixture for mremap tests parameterized by mmap flags.
 using MremapParamTest = ::testing::TestWithParam<int>;