Re: [PATCH] module: add in-kernel support for decompressing

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>
---

I am also attaching a patch to kmod to make use of this new facility.

Thanks!

 include/uapi/linux/module.h |   1 +
 init/Kconfig                |  12 ++
 kernel/Makefile             |   1 +
 kernel/module-internal.h    |  18 +++
 kernel/module.c             |  35 +++--
 kernel/module_decompress.c  | 271 ++++++++++++++++++++++++++++++++++++
 6 files changed, 327 insertions(+), 11 deletions(-)

diff --git a/include/uapi/linux/module.h b/include/uapi/linux/module.h
index 50d98ec5e866..becab4a1c5db 100644
--- a/include/uapi/linux/module.h
+++ b/include/uapi/linux/module.h

@@ -5,5 +5,6 @@
 /* Flags for sys_finit_module: */
 #define MODULE_INIT_IGNORE_MODVERSIONS	1
 #define MODULE_INIT_IGNORE_VERMAGIC	2
+#define MODULE_INIT_COMPRESSED_DATA	4

 
 #endif /* _UAPI_LINUX_MODULE_H */

diff --git a/init/Kconfig b/init/Kconfig
index 03d3c21e28a3..a3f37ae7436d 100644
--- a/init/Kconfig
+++ b/init/Kconfig

@@ -2309,6 +2309,18 @@ config MODULE_COMPRESS_ZSTD
 
 endchoice
 
+config MODULE_DECOMPRESS
+	bool "Support in-kernel module decompression"
+	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

diff --git a/kernel/Makefile b/kernel/Makefile
index 186c49582f45..56f4ee97f328 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile

@@ -67,6 +67,7 @@ obj-y += up.o
 endif
 obj-$(CONFIG_UID16) += uid16.o
 obj-$(CONFIG_MODULES) += module.o
+obj-$(CONFIG_MODULE_DECOMPRESS) += module_decompress.o
 obj-$(CONFIG_MODULE_SIG) += module_signing.o
 obj-$(CONFIG_MODULE_SIG_FORMAT) += module_signature.o
 obj-$(CONFIG_KALLSYMS) += kallsyms.o

diff --git a/kernel/module-internal.h b/kernel/module-internal.h
index 33783abc377b..3c1143d2c8c7 100644
--- a/kernel/module-internal.h
+++ b/kernel/module-internal.h

@@ -22,6 +22,11 @@ struct load_info {
 	bool sig_ok;
 #ifdef CONFIG_KALLSYMS
 	unsigned long mod_kallsyms_init_off;
+#endif
+#ifdef CONFIG_MODULE_DECOMPRESS
+	struct page **pages;
+	unsigned int max_pages;
+	unsigned int used_pages;
 #endif
 	struct {
 		unsigned int sym, str, mod, vers, info, pcpu;

@@ -29,3 +34,16 @@ struct load_info {
 };
 
 extern int mod_verify_sig(const void *mod, struct load_info *info);
+
+#ifdef CONFIG_MODULE_DECOMPRESS
+int module_decompress(struct load_info *info, const void *buf, size_t size);
+void module_decompress_cleanup(struct load_info *info);
+#else
+int module_decompress(struct load_info *info, const void *buf, size_t size)
+{
+	return -EOPNOTSUPP;
+}
+void module_decompress_cleanup(struct load_info *info)
+{
+}
+#endif

diff --git a/kernel/module.c b/kernel/module.c
index 84a9141a5e15..eeab85ea1627 100644
--- a/kernel/module.c
+++ b/kernel/module.c

@@ -3174,9 +3174,12 @@ static int copy_module_from_user(const void __user *umod, unsigned long len,
 	return err;
 }
 
-static void free_copy(struct load_info *info)
+static void free_copy(struct load_info *info, int flags)

 {
-	vfree(info->hdr);
+	if (flags & MODULE_INIT_COMPRESSED_DATA)
+		module_decompress_cleanup(info);
+	else
+		vfree(info->hdr);
 }
 
 static int rewrite_section_headers(struct load_info *info, int flags)

@@ -4125,7 +4128,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
 	}
 
 	/* Get rid of temporary copy. */
-	free_copy(info);
+	free_copy(info, flags);
 
 	/* Done! */
 	trace_module_load(mod);

@@ -4174,7 +4177,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
 
 	module_deallocate(mod, info);
  free_copy:
-	free_copy(info);
+	free_copy(info, flags);
 	return err;
 }
 

@@ -4201,7 +4204,8 @@ SYSCALL_DEFINE3(init_module, void __user *, umod,
 SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
 {
 	struct load_info info = { };
-	void *hdr = NULL;
+	void *buf = NULL;
+	int len;
 	int err;
 
 	err = may_init_module();

@@ -4211,15 +4215,24 @@ SYSCALL_DEFINE3(finit_module, int, fd, const char __user *, uargs, int, flags)
 	pr_debug("finit_module: fd=%d, uargs=%p, flags=%i\n", fd, uargs, flags);
 
 	if (flags & ~(MODULE_INIT_IGNORE_MODVERSIONS
-		      |MODULE_INIT_IGNORE_VERMAGIC))
+		      |MODULE_INIT_IGNORE_VERMAGIC
+		      |MODULE_INIT_COMPRESSED_DATA))
 		return -EINVAL;
 
-	err = kernel_read_file_from_fd(fd, 0, &hdr, INT_MAX, NULL,
+	len = kernel_read_file_from_fd(fd, 0, &buf, INT_MAX, NULL,
 				       READING_MODULE);
-	if (err < 0)
-		return err;
-	info.hdr = hdr;
-	info.len = err;
+	if (len < 0)
+		return len;
+
+	if (flags & MODULE_INIT_COMPRESSED_DATA) {
+		err = module_decompress(&info, buf, len);
+		vfree(buf); /* compressed data is no longer needed */
+		if (err)
+			return err;
+	} else {
+		info.hdr = buf;
+		info.len = len;
+	}
 
 	return load_module(&info, uargs, flags);
 }

diff --git a/kernel/module_decompress.c b/kernel/module_decompress.c
new file mode 100644
index 000000000000..590ca00aa098
--- /dev/null
+++ b/kernel/module_decompress.c