libkmod: Use kernel decompression when availabletip-module-decompression

With the recent changes to bypass loading the file it's possible to
reduce the work in userspace and delegating it to the kernel. Without
any compression to illustrate:

Before:
	read(3, "\177ELF\2\1", 6)               = 6
	lseek(3, 0, SEEK_SET)                   = 0
	newfstatat(3, "", {st_mode=S_IFREG|0644, st_size=238592, ...}, AT_EMPTY_PATH) = 0
	mmap(NULL, 238592, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fd85cbd1000
	finit_module(3, "", 0)                  = 0
	munmap(0x7fd85cbd1000, 238592)          = 0
	close(3)                                = 0

After:
	read(3, "\177ELF\2\1", 6)               = 6
	lseek(3, 0, SEEK_SET)                   = 0
	finit_module(3, "", 0)                  = 0
	close(3)                                = 0

When using kernel compression now it's also possible to direct libkmod
to take the finit_module() path, avoiding the decompression in userspace
and just delegating it to the kernel.

Before:
	read(3, "(\265/\375\244\0", 6)          = 6
	lseek(3, 0, SEEK_SET)                   = 0
	read(3, "(\265/\375\244", 5)            = 5
	mmap(NULL, 135168, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3fa431e000
	read(3, "\0\244\3\0\\y\6", 7)           = 7
	mmap(NULL, 372736, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3fa414f000
	brk(0x55944c6a1000)                     = 0x55944c6a1000
	read(3, "\356|\6G\27U\20 \312\260s\211\335\333\263\326\330\336\273O\211\356\306K\360Z\341\374U6\342\221"..., 53038) = 53038
	mremap(0x7f3fa431e000, 135168, 266240, MREMAP_MAYMOVE) = 0x7f3fa410e000
	read(3, ",;\3\nqf\311\362\325\211\7\341\375A\355\221\371L\\\5\7\375 \32\246<(\258=K\304"..., 20851) = 20851
	mremap(0x7f3fa410e000, 266240, 397312, MREMAP_MAYMOVE) = 0x7f3fa40ad000
	read(3, ")\36\250\213", 4)              = 4
	read(3, "", 4)                          = 0
	munmap(0x7f3fa414f000, 372736)          = 0
	init_module(0x7f3fa40ad010, 238592, "") = 0
	munmap(0x7f3fa40ad000, 397312)          = 0
	close(3)                                = 0

After:
	read(3, "\37\213\10\10\27H", 6)         = 6
	lseek(3, 0, SEEK_SET)                   = 0
	finit_module(3, "", MODULE_INIT_COMPRESSED_FILE) = 0
	close(3)                                = 0

FIXME: note that the last case is using zlib compression instead of
zstd. Something is broken in the kernel when decompressing the module
via zstd and in that case the module fails to load.

Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>

4 files changed, 37 insertions, 13 deletions

diff --git a/libkmod/libkmod-file.c b/libkmod/libkmod-file.c
index 705770a..ffdda92 100644
--- a/libkmod/libkmod-file.c
+++ b/libkmod/libkmod-file.c
@@ -513,9 +513,9 @@ off_t kmod_file_get_size(const struct kmod_file *file)
 	return file->size;
 }
 
-bool kmod_file_get_direct(const struct kmod_file *file)
+enum kmod_file_compression_type kmod_file_get_compression(const struct kmod_file *file)
 {
-	return file->compression == KMOD_FILE_COMPRESSION_NONE;
+	return file->compression;
 }
 
 int kmod_file_get_fd(const struct kmod_file *file)
diff --git a/libkmod/libkmod-internal.h b/libkmod/libkmod-internal.h
index 91c413b..edb4eac 100644
--- a/libkmod/libkmod-internal.h
+++ b/libkmod/libkmod-internal.h
@@ -61,6 +61,13 @@ struct kmod_list {
 	void *data;
 };
 
+enum kmod_file_compression_type {
+	KMOD_FILE_COMPRESSION_NONE = 0,
+	KMOD_FILE_COMPRESSION_ZSTD,
+	KMOD_FILE_COMPRESSION_XZ,
+	KMOD_FILE_COMPRESSION_ZLIB,
+};
+
 struct kmod_list *kmod_list_append(struct kmod_list *list, const void *data) _must_check_ __attribute__((nonnull(2)));
 struct kmod_list *kmod_list_prepend(struct kmod_list *list, const void *data) _must_check_ __attribute__((nonnull(2)));
 struct kmod_list *kmod_list_remove(struct kmod_list *list) _must_check_;
@@ -105,6 +112,7 @@ void kmod_pool_add_module(struct kmod_ctx *ctx, struct kmod_module *mod, const c
 void kmod_pool_del_module(struct kmod_ctx *ctx, struct kmod_module *mod, const char *key) __attribute__((nonnull(1, 2, 3)));
 
 const struct kmod_config *kmod_get_config(const struct kmod_ctx *ctx) __attribute__((nonnull(1)));
+enum kmod_file_compression_type kmod_get_kernel_compression(const struct kmod_ctx *ctx) __attribute__((nonnull(1)));
 
 /* libkmod-config.c */
 struct kmod_config_path {
@@ -150,19 +158,12 @@ void kmod_module_set_required(struct kmod_module *mod, bool required) __attribut
 bool kmod_module_is_builtin(struct kmod_module *mod) __attribute__((nonnull(1)));
 
 /* libkmod-file.c */
-enum kmod_file_compression_type {
-	KMOD_FILE_COMPRESSION_NONE = 0,
-	KMOD_FILE_COMPRESSION_ZSTD,
-	KMOD_FILE_COMPRESSION_XZ,
-	KMOD_FILE_COMPRESSION_ZLIB,
-};
-
 struct kmod_file *kmod_file_open(const struct kmod_ctx *ctx, const char *filename) _must_check_ __attribute__((nonnull(1,2)));
 struct kmod_elf *kmod_file_get_elf(struct kmod_file *file) __attribute__((nonnull(1)));
 int kmod_file_load_contents(struct kmod_file *file) _must_check_ __attribute__((nonnull(1)));
 void *kmod_file_get_contents(const struct kmod_file *file) _must_check_ __attribute__((nonnull(1)));
 off_t kmod_file_get_size(const struct kmod_file *file) _must_check_ __attribute__((nonnull(1)));
-bool kmod_file_get_direct(const struct kmod_file *file) _must_check_ __attribute__((nonnull(1)));
+enum kmod_file_compression_type kmod_file_get_compression(const struct kmod_file *file) _must_check_ __attribute__((nonnull(1)));
 int kmod_file_get_fd(const struct kmod_file *file) _must_check_ __attribute__((nonnull(1)));
 void kmod_file_unref(struct kmod_file *file) __attribute__((nonnull(1)));
 
diff --git a/libkmod/libkmod-module.c b/libkmod/libkmod-module.c
index 6ed5ad4..76de43d 100644
--- a/libkmod/libkmod-module.c
+++ b/libkmod/libkmod-module.c
@@ -861,19 +861,37 @@ KMOD_EXPORT int kmod_module_remove_module(struct kmod_module *mod,
 
 extern long init_module(const void *mem, unsigned long len, const char *args);
 
+static bool has_builtin_kernel_compression_support(void)
+{
+#ifdef MODULE_INIT_COMPRESSED_FILE
+	return true;
+#endif
+	return false;
+}
+
 static int do_finit_module(struct kmod_module *mod, unsigned int flags,
 			   const char *args)
 {
+	enum kmod_file_compression_type compression, kernel_compression;
 	unsigned int kernel_flags = 0;
 	int err;
 
 	/*
-	 * Re-use ENOSYS, returned when there is no such syscall, so the
-	 * fallback to init_module applies
+	 * When module is not compressed or its compression type matches the
+	 * one in use by the kernel, there is no need to read the file
+	 * in userspace. Otherwise, re-use ENOSYS to trigger the same fallback
+	 * as when finit_module() is not supported.
 	 */
-	if (!kmod_file_get_direct(mod->file))
+	compression = kmod_file_get_compression(mod->file);
+	kernel_compression = kmod_get_kernel_compression(mod->ctx);
+	if (compression != KMOD_FILE_COMPRESSION_NONE &&
+	    (!has_builtin_kernel_compression_support() ||
+	     compression != kernel_compression))
 		return -ENOSYS;
 
+	if (compression == kernel_compression)
+		kernel_flags |= MODULE_INIT_COMPRESSED_FILE;
+
 	if (flags & KMOD_INSERT_FORCE_VERMAGIC)
 		kernel_flags |= MODULE_INIT_IGNORE_VERMAGIC;
 	if (flags & KMOD_INSERT_FORCE_MODVERSION)
diff --git a/libkmod/libkmod.c b/libkmod/libkmod.c
index 103469e..1b8773c 100644
--- a/libkmod/libkmod.c
+++ b/libkmod/libkmod.c
@@ -1016,3 +1016,8 @@ const struct kmod_config *kmod_get_config(const struct kmod_ctx *ctx)
 {
 	return ctx->config;
 }
+
+enum kmod_file_compression_type kmod_get_kernel_compression(const struct kmod_ctx *ctx)
+{
+	return ctx->kernel_compression;
+}