module: add in-kernel support for decompressing

Current scheme of having userspace decompress kernel modules before
loading them into the kernel runs afoul of LoadPin security policy, as
it loses link between the source of kernel module on the disk and binary
blob that is being loaded into the kernel. To solve this issue let's
implement decompression in kernel, so that we can pass a file descriptor
of compressed module file into finit_module() which will keep LoadPin
happy.

To let userspace know what compression/decompression scheme kernel
supports it will create /sys/module/compression attribute. kmod can read
this attribute and decide if it can pass compressed file to
finit_module(). New MODULE_INIT_COMPRESSED_DATA flag indicates that the
kernel should attempt to decompress the data read from file descriptor
prior to trying load the module.

To simplify things kernel will only implement single decompression
method matching compression method selected when generating modules.
This patch implements gzip and xz; more can be added later,

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index f2ae41e6717f..faf3a4b5cc8f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -2274,6 +2274,19 @@ config MODULE_COMPRESS_ZSTD
 
 endchoice
 
+config MODULE_DECOMPRESS
+	bool "Support in-kernel module decompression"
+	depends on MODULE_COMPRESS_GZIP || MODULE_COMPRESS_XZ
+	select ZLIB_INFLATE if MODULE_COMPRESS_GZIP
+	select XZ_DEC if MODULE_COMPRESS_XZ
+	help
+
+	  Support for decompressing kernel modules by the kernel itself
+	  instead of relying on userspace to perform this task. Useful when
+	  load pinning security policy is enabled.
+
+	  If unsure, say N.
+
 config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
 	bool "Allow loading of modules with missing namespace imports"
 	help