kernel-cmdline: add size check

Add check to ensure that the size of
the parameters does not exceed the
maximum kernel cmdline size.
Otherwise, the parameters will
be truncated and the command line
will fail.

The size is arch-dependant. In
order to not to over-complicate
the search of the value in the
kernel files (which will probably
not be installed in most cases),
it uses a map with some values
for common architectures.

If architecture is not found in
the map, defaults to 4096, which
is the maximum posible size for
COMMAND_LINE_SIZE.

Signed-off-by: Albert Esteve <aesteve@redhat.com>

stages/org.osbuild.kernel-cmdline

@@ -1,13 +1,35 @@
 #!/usr/bin/python3
 import os
+import platform
 import sys
 
 import osbuild.api
 
+# COMMAND_LINE_SIZE value per arch
+MAX_SIZE_MAP = {
+    # https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/setup.h
+    "x86_64": 2048,
+    # https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/setup.h
+    "i386": 2048,
+    # https://github.com/torvalds/linux/blame/master/arch/arm/include/uapi/asm/setup.h
+    "arm": 1024,
+    # https://github.com/torvalds/linux/blob/master/arch/arm64/include/uapi/asm/setup.h
+    "aarch64": 2048,
+    # https://github.com/torvalds/linux/blob/master/arch/powerpc/include/uapi/asm/setup.h
+    "powerpc": 2048,
+    # https://github.com/torvalds/linux/blob/master/arch/powerpc/include/uapi/asm/setup.h
+    "ppc64": 2048,
+    # https://github.com/torvalds/linux/blob/master/arch/riscv/include/uapi/asm/setup.h
+    "riscv": 1024,
+    # https://github.com/torvalds/linux/blob/master/arch/mips/include/uapi/asm/setup.h
+    "mips": 4096
+}
+
 
 def main(tree, options):
     root_fs_uuid = options.get("root_fs_uuid", "")
     additional = options.get("kernel_opts", "")
+    max_cmdline_size = MAX_SIZE_MAP.get(platform.machine().lower(), 4096)
 
     params = []
 
@@ -17,11 +39,16 @@ def main(tree, options):
     if additional:
         params += [additional]
 
+    params = " ".join(filter(len, params))
+    if len(params) > max_cmdline_size:
+        raise ValueError("The size of the kernel cmdline options cannot be "
+                         f"larger than {max_cmdline_size}")
+
     base = os.path.join(tree, "etc/kernel")
     os.makedirs(base, exist_ok=True)
 
     with open(f"{base}/cmdline", "w", encoding="utf8") as f:
-        f.write(" ".join(filter(len, params)))
+        f.write(params)
 
     return 0