fix: copy_file skip files larger than 1GB (Fixes #4039)

Author: iamhuskar

CMakeLists.txt

@@ -1188,6 +1188,7 @@ set(BASIC_TESTS
   memfd_create_efault
   memfd_create_shared
   memfd_create_shared_huge
+  memfd_create_dotnet_huge_mapping
   mincore
   mknod
   mlock

src/TraceStream.cc

@@ -995,10 +995,13 @@ TraceWriter::RecordInTrace TraceWriter::write_mapped_region(
     // debuggers can't find the file, but the Linux loader doesn't create
     // shared mappings so situations where a shared-mapped executable contains
     // usable debug info should be very rare at best...
+    // copy files when the mapping is PROT_EXEC, unless the file is too big
+    // sometimes km.size() does not equal the file size from fstat().
     string backing_file_name;
     if ((km.prot() & PROT_EXEC) &&
-        copy_file(km.fsname(), file_name, &backing_file_name) &&
-        !(km.flags() & MAP_SHARED)) {
+        !(km.flags() & MAP_SHARED) &&
+        stat.st_size <= 1024 * 1024 * 1024 &&
+        copy_file(km.fsname(), file_name, &backing_file_name)) {
       src.initFile().setBackingFileName(str_to_data(backing_file_name));
     } else {
       src.setTrace();

src/test/memfd_create_dotnet_huge_mapping.c

@@ -0,0 +1,37 @@
+#include "util.h"
+/*
+https://github.com/dotnet/runtime/blob/23aeecc9f91a9ae0a211702dbd849c90cdd81d36/src/coreclr/minipal/Unix/doublemapping.cpp#L85
+#ifdef TARGET_64BIT
+static const off_t MaxDoubleMappedSize = 2048ULL*1024*1024*1024;
+#else
+static const off_t MaxDoubleMappedSize = UINT_MAX;
+#endif
+To prevent bugs that could result in writing a 2TB file, a 20GB limit is used instead.
+*/
+#define _1GB (1024 * 1024 * 1024ULL)
+unsigned long long MaxDoubleMappedSize = 20 * _1GB;
+#define PAGE_SIZE_4K 4096
+
+void test_ftruncate_huge_mapping(void) {
+  int fd = memfd_create("double_mapper_test", MFD_CLOEXEC);
+  test_assert(fd >= 0);
+  test_assert(ftruncate(fd, MaxDoubleMappedSize) == 0);
+  void* executable_addr = mmap(NULL, PAGE_SIZE_4K, PROT_READ | PROT_EXEC, MAP_PRIVATE, fd, 0);
+  test_assert(executable_addr != MAP_FAILED);
+  test_assert(0 == close(fd));
+}
+
+int main(void) {
+#if defined(__i386__)
+  atomic_puts("Skipping test on 32 bit");
+#else
+  struct timespec start, end;
+  test_assert(-1 != clock_gettime(CLOCK_MONOTONIC, &start));
+  test_ftruncate_huge_mapping();
+  test_assert(-1 != clock_gettime(CLOCK_MONOTONIC, &end));
+  //check timeout
+  test_assert((end.tv_sec - start.tv_sec) <= 2);
+#endif
+  atomic_puts("EXIT-SUCCESS");
+  return 0;
+}