From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: netdev@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
"David S . Miller" <davem@davemloft.net>,
Arnd Bergmann <arnd@arndb.de>,
Geert Uytterhoeven <geert@linux-m68k.org>,
linux-kernel@vger.kernel.org, YueHaibing <yuehaibing@huawei.com>,
Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH v2 2/3] bpfilter: include bpfilter_umh in assembly instead of using objcopy
Date: Thu, 14 Jun 2018 17:47:06 -0700 [thread overview]
Message-ID: <20180615004704.u5gofft7k6ehmhwi@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <1528987172-19810-3-git-send-email-yamada.masahiro@socionext.com>
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.
next prev parent reply other threads:[~2018-06-15 0:47 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-14 14:39 [PATCH v2 0/3] net: bpfilter: clean-up build rules Masahiro Yamada
2018-06-14 14:39 ` [PATCH v2 1/3] bpfilter: add bpfilter_umh to .gitignore Masahiro Yamada
2018-06-14 14:39 ` [PATCH v2 2/3] bpfilter: include bpfilter_umh in assembly instead of using objcopy Masahiro Yamada
2018-06-15 0:47 ` Alexei Starovoitov [this message]
2018-06-26 3:44 ` Masahiro Yamada
2019-01-31 10:48 ` Janne Karhunen
2019-01-31 11:09 ` Janne Karhunen
2019-01-31 12:40 ` Janne Karhunen
2018-06-14 14:39 ` [PATCH v2 3/3] bpfilter: check compiler capability in Kconfig Masahiro Yamada
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