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Date: Thu, 14 Jun 2018 17:47:06 -0700 From: Alexei Starovoitov <alexei.starovoitov@...il.com> To: Masahiro Yamada <yamada.masahiro@...ionext.com> Cc: netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>, "David S . Miller" <davem@...emloft.net>, Arnd Bergmann <arnd@...db.de>, Geert Uytterhoeven <geert@...ux-m68k.org>, linux-kernel@...r.kernel.org, YueHaibing <yuehaibing@...wei.com>, Daniel Borkmann <daniel@...earbox.net> Subject: Re: [PATCH v2 2/3] bpfilter: include bpfilter_umh in assembly instead of using objcopy On Thu, Jun 14, 2018 at 11:39:31PM +0900, Masahiro Yamada wrote: > What we want here is to embed a user-space program into the kernel. > Instead of the complex ELF magic, let's simply wrap it in the assembly > with the '.incbin' directive. > > Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com> > --- > > Changes in v2: > - Rebase > > 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 e0bbe75..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; \ > - $(OBJCOPY) -I binary -O `$(OBJDUMP) -f $<|grep format|cut -d' ' -f8` \ > - -B `$(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 0952257..6de3ae5 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 */ > @@ -93,7 +90,9 @@ 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: for some reason it doesn't work. fork_usermode_blob() returns ENOEXEC You should be able to test it simply running 'iptables -L'. Without this patch you should see: [ 12.696937] bpfilter: Loaded bpfilter_umh pid 225 Started bpfilter where first line comes from kernel module and second from umh.
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