[PATCH 2/3] bpfilter: include bpfilter_umh in assembly instead of using objcopy

[Masahiro Yamada]

Do not use the troublesome ELF magic.  What is happening here is to
embed a user-space program into the kernel.  Simply wrap it in the
assembly with the '.incbin' directive.

Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
---

 net/bpfilter/Makefile            | 15 ++-------------
 net/bpfilter/bpfilter_kern.c     | 11 +++++------
 net/bpfilter/bpfilter_umh_blob.S |  7 +++++++
 3 files changed, 14 insertions(+), 19 deletions(-)
 create mode 100644 net/bpfilter/bpfilter_umh_blob.S

diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile
index aafa720..39c6980 100644
--- a/net/bpfilter/Makefile
+++ b/net/bpfilter/Makefile
@@ -15,18 +15,7 @@ ifeq ($(CONFIG_BPFILTER_UMH), y)
 HOSTLDFLAGS += -static
 endif
 
-# a bit of elf magic to convert bpfilter_umh binary into a binary blob
-# inside bpfilter_umh.o elf file referenced by
-# _binary_net_bpfilter_bpfilter_umh_start symbol
-# which bpfilter_kern.c passes further into umh blob loader at run-time
-quiet_cmd_copy_umh = GEN $@
-      cmd_copy_umh = echo ':' > $(obj)/.bpfilter_umh.o.cmd; \
-      $(OBJCOPY) -I binary -O $(CONFIG_OUTPUT_FORMAT) \
-      -B `$(OBJDUMP) -f $<|grep architecture|cut -d, -f1|cut -d' ' -f2` \
-      --rename-section .data=.init.rodata $< $@
-
-$(obj)/bpfilter_umh.o: $(obj)/bpfilter_umh
-	$(call cmd,copy_umh)
+$(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh
 
 obj-$(CONFIG_BPFILTER_UMH) += bpfilter.o
-bpfilter-objs += bpfilter_kern.o bpfilter_umh.o
+bpfilter-objs += bpfilter_kern.o bpfilter_umh_blob.o
diff --git a/net/bpfilter/bpfilter_kern.c b/net/bpfilter/bpfilter_kern.c
index b13d058..fcc1a7c 100644
--- a/net/bpfilter/bpfilter_kern.c
+++ b/net/bpfilter/bpfilter_kern.c
@@ -10,11 +10,8 @@
 #include <linux/file.h>
 #include "msgfmt.h"
 
-#define UMH_start _binary_net_bpfilter_bpfilter_umh_start
-#define UMH_end _binary_net_bpfilter_bpfilter_umh_end
-
-extern char UMH_start;
-extern char UMH_end;
+extern char bpfilter_umh_start;
+extern char bpfilter_umh_end;
 
 static struct umh_info info;
 /* since ip_getsockopt() can run in parallel, serialize access to umh */
@@ -89,7 +86,9 @@ static int __init load_umh(void)
 	int err;
 
 	/* fork usermode process */
-	err = fork_usermode_blob(&UMH_start, &UMH_end - &UMH_start, &info);
+	err = fork_usermode_blob(&bpfilter_umh_end,
+				 &bpfilter_umh_end - &bpfilter_umh_start,
+				 &info);
 	if (err)
 		return err;
 	pr_info("Loaded bpfilter_umh pid %d\n", info.pid);
diff --git a/net/bpfilter/bpfilter_umh_blob.S b/net/bpfilter/bpfilter_umh_blob.S
new file mode 100644
index 0000000..40311d1
--- /dev/null
+++ b/net/bpfilter/bpfilter_umh_blob.S
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+	.section .init.rodata, "a"
+	.global bpfilter_umh_start
+bpfilter_umh_start:
+	.incbin "net/bpfilter/bpfilter_umh"
+	.global bpfilter_umh_end
+bpfilter_umh_end:
-- 
2.7.4