file: Support reading EFI zboot images

ecleankernel/file.py

@@ -111,7 +111,10 @@ def __init__(self,
         super().__init__(path, KernelFileType.KERNEL)
         self.internal_version = self.read_internal_version()
 
-    def decompress_raw(self, f: typing.IO[bytes]) -> bytes:
+    def decompress_raw(self,
+                       f: typing.IO[bytes],
+                       size: typing.Optional[int] = None,
+                       ) -> bytes:
         magic_dict = {
             b'\x1f\x8b\x08': 'gzip',
             b'\x42\x5a\x68': 'bz2',
@@ -122,8 +125,11 @@ def decompress_raw(self, f: typing.IO[bytes]) -> bytes:
             b'\x89\x4c\x5a\x4f\x00\x0d\x0a\x1a\x0a': 'lzo',
         }
         maxlen = max(len(x) for x in magic_dict)
+        if size and maxlen > size:
+            return f.read(size)
         with autorewind(f):
             header = f.read(maxlen)
+        buffer = f.read(size or -1)
         for magic, comp in magic_dict.items():
             if header.startswith(magic):
                 try:
@@ -137,21 +143,15 @@ def decompress_raw(self, f: typing.IO[bytes]) -> bytes:
                     # Technically a redundant import, this is just
                     # to make your IDE happy :)
                     import zstandard
-                    reader = zstandard.ZstdDecompressor().stream_reader(f)
-                    decomp = b''
-                    while True:
-                        chunk = reader.read(1024 * 1024)
-                        if not chunk:
-                            break
-                        decomp += chunk
-                    return decomp
+                    decompress = zstandard.ZstdDecompressor().decompressobj()
+                    return decompress(buffer)
                 elif comp == 'lzma':
                     # Using .decompress() causes an error because of
                     # no end-of-stream marker
-                    return LZMADecompressor().decompress(f.read())
+                    return LZMADecompressor().decompress(buffer)
                 else:
-                    return getattr(mod, 'decompress')(f.read())
-        return f.read()
+                    return getattr(mod, 'decompress')(buffer)
+        return buffer
 
     def read_internal_version(self) -> str:
         """Read version from the kernel file"""
@@ -199,11 +199,12 @@ def read_version_from_bzimage(self,
 
     def read_version_from_raw(self,
                               f: typing.IO[bytes],
+                              size: typing.Optional[int] = None,
                               ) -> typing.Optional[bytes]:
         """Read version from raw kernel image"""
 
         # check if it's compressed first
-        b = self.decompress_raw(f)
+        b = self.decompress_raw(f, size)
         # unlike with bzImage, the raw kernel binary has no header
         # that includes the version, so we parse the version message
         # that appears on boot
@@ -226,6 +227,14 @@ def read_version_from_efi(self,
             buf = f.read(0x40)
             if len(buf) != 0x40 or buf[:2] != b"MZ":
                 return None
+
+            # handle EFI zboot image
+            # see kernel source code drivers/firmware/efi/libstub/zboot-header.S
+            if buf[4:8] == b"zimg":
+                offset, size = struct.unpack_from("<LL", buf, 8)
+                f.seek(offset)
+                return self.read_version_from_raw(f, size)
+
             coff_offset = struct.unpack_from("<L", buf, 0x3c)[0]
 
             # at offset, we find PE\0\0 signature and COFF file header

test/test_file.py

@@ -4,6 +4,7 @@
 import gzip
 import hashlib
 import os
+import struct
 import tempfile
 import unittest
 
@@ -98,6 +99,22 @@ def write_efistub(path: Path,
             f.write(version_line)
 
 
+def write_efi_zboot(path: Path,
+                    version_line: bytes,
+                    ) -> None:
+    """Write an EFI zboot kernel image at `path`, with `version_line`"""
+    # generate a compressed image as our payload
+    write_compress(path, version_line)
+    b = path.read_bytes()
+
+    with open(path, "wb") as f:
+        f.write(b"MZ\0\0zimg")
+        f.write(struct.pack("<LL", 0x40, len(b)))
+        f.write(8 * b"\0" + b"gzip" + 4 * b"\0")
+        f.write(0x20 * b"\0")
+        f.write(b)
+
+
 class KernelImageTests(unittest.TestCase):
     def setUp(self) -> None:
         self.td = tempfile.TemporaryDirectory()
@@ -147,6 +164,13 @@ def test_read_internal_version_efistub_uname_nowhitespace(self) -> None:
             KernelImage(path).read_internal_version(),
             "1.2.3")
 
+    def test_read_internal_version_efi_zboot(self) -> None:
+        path = Path(self.td.name) / "vmlinuz"
+        write_efi_zboot(path, b"Linux version 1.2.3 built on test")
+        self.assertEqual(
+            KernelImage(path).read_internal_version(),
+            "1.2.3")
+
     def test_very_short(self) -> None:
         path = Path(self.td.name) / 'vmlinuz'
         with open(path, 'wb') as f: