Merge pull request #1634 from retrocpugeek/fix/statx-bigendian

Fix statx byte order on big-endian guests

Author: xwings

qiling/os/posix/syscall/stat.py

@@ -1413,17 +1413,45 @@ class Statx64(ctypes.Structure):
 
     _pack_ = 4
 
+# Big-endian counterparts of the statx structs. The kernel statx layout is the
+# same on every architecture, so the big-endian variants reuse the little-endian
+# field lists verbatim and only change the ctypes base class (and the nested
+# timestamp type, which must itself be big-endian). Without these, statx() byte-
+# swaps every field on a big-endian guest (e.g. MIPS/MIPS64 EB), so stx_mode
+# loses its S_IFDIR bit and tools like `ls` treat directories as plain files.
+class StatxTimestamp32EB(ctypes.BigEndianStructure):
+    _fields_ = StatxTimestamp32._fields_
+
+class StatxTimestamp64EB(ctypes.BigEndianStructure):
+    _fields_ = StatxTimestamp64._fields_
+
+def _statx_fields_eb(fields):
+    swap = {StatxTimestamp32: StatxTimestamp32EB, StatxTimestamp64: StatxTimestamp64EB}
+    return [(name, swap.get(ftype, ftype)) for (name, ftype) in fields]
+
+class Statx32EB(ctypes.BigEndianStructure):
+    _fields_ = _statx_fields_eb(Statx32._fields_)
+    _pack_ = 8
+
+class Statx64EB(ctypes.BigEndianStructure):
+    _fields_ = _statx_fields_eb(Statx64._fields_)
+    _pack_ = 4
+
 # int statx(int dirfd, const char *restrict pathname, int flags,
 #                  unsigned int mask, struct statx *restrict statxbuf);
 def ql_syscall_statx(ql: Qiling, dirfd: int, path: int, flags: int, mask: int, buf_ptr: int):
+    is_eb = ql.arch.endian == QL_ENDIAN.EB
+
     def statx_convert_timestamp(tv_sec, tv_nsec):
         tv_sec  = struct.unpack('i', struct.pack('f', tv_sec))[0]
         tv_nsec = struct.unpack('i', struct.pack('f', tv_nsec))[0]
 
         if ql.arch.bits == 32:
-            return StatxTimestamp32(tv_sec=tv_sec, tv_nsec=tv_nsec)
+            Timestamp = StatxTimestamp32EB if is_eb else StatxTimestamp32
         else:
-            return StatxTimestamp64(tv_sec=tv_sec, tv_nsec=tv_nsec)
+            Timestamp = StatxTimestamp64EB if is_eb else StatxTimestamp64
+
+        return Timestamp(tv_sec=tv_sec, tv_nsec=tv_nsec)
 
 
     def major(dev):
@@ -1438,9 +1466,9 @@ def minor(dev):
         st = Stat(real_path, fd)
 
         if ql.arch.bits == 32:
-            Statx = Statx32
+            Statx = Statx32EB if is_eb else Statx32
         else:
-            Statx = Statx64
+            Statx = Statx64EB if is_eb else Statx64
 
         stx = Statx(
             stx_mask = 0x07ff, # STATX_BASIC_STATS

tests/test_elf.py

@@ -836,6 +836,37 @@ def test_linux_getdents_alignment(self):
 
         del ql
 
+    # Regression for statx() byte order on big-endian guests: the statx struct
+    # must be serialized in the guest's endianness. Otherwise stx_mode is byte-
+    # swapped and a directory loses its S_IFDIR bit (so e.g. `ls` treats a
+    # directory as a regular file). Exercised on a big-endian MIPS context.
+    def test_linux_statx_bigendian(self):
+        import stat as _stat
+        from qiling.const import QL_ENDIAN
+        from qiling.os.posix.syscall.stat import ql_syscall_statx, Statx32
+
+        ql = Qiling(code=b"\x00\x00\x00\x00", archtype=QL_ARCH.MIPS, ostype=QL_OS.LINUX,
+                    endian=QL_ENDIAN.EB, rootfs="../examples/rootfs/mips32_linux",
+                    verbose=QL_VERBOSE.OFF)
+
+        base = 0x100000
+        ql.mem.map(base, 0x1000)
+        path_ptr, buf_ptr = base, base + 0x200
+        ql.mem.write(path_ptr, b"/\x00")
+
+        AT_FDCWD = -100 & 0xffffffff
+        STATX_BASIC_STATS = 0x07ff
+        ret = ql_syscall_statx(ql, AT_FDCWD, path_ptr, 0, STATX_BASIC_STATS, buf_ptr)
+        self.assertEqual(ret, 0)
+
+        # the guest is big-endian, so it reads stx_mode in big-endian byte order;
+        # it must come back as a directory (S_IFDIR). Before the fix the struct
+        # was emitted little-endian and the type bits were lost.
+        mode = int.from_bytes(ql.mem.read(buf_ptr + Statx32.stx_mode.offset, 2), 'big')
+        self.assertTrue(_stat.S_ISDIR(mode))
+
+        del ql
+
     def test_memory_search(self):
         ql = Qiling(code=b"\xCC", archtype=QL_ARCH.X8664, ostype=QL_OS.LINUX, verbose=QL_VERBOSE.DEBUG)