Messages in this thread | | | From | Janne Karhunen <> | Date | Thu, 31 Jan 2019 12:48:33 +0200 | Subject | Re: [PATCH v2 2/3] bpfilter: include bpfilter_umh in assembly instead of using objcopy |
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Hi,
Hmm, does this approach work if the code is not in a kernel module? I tried to use it as part of the kernel image and looks to me the bounding symbols _start and _end are not correctly relocated?
-- Janne
On Fri, Jun 15, 2018 at 3:48 AM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote: > > 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@socionext.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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