[v2,2/3] bpfilter: include bpfilter_umh in assembly instead of using objcopy

Message ID 1528987172-19810-3-git-send-email-yamada.masahiro@socionext.com
State New
Headers show
Series
  • net: bpfilter: clean-up build rules
Related show

Commit Message

Masahiro Yamada June 14, 2018, 2:39 p.m.
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

-- 
2.7.4

Comments

Alexei Starovoitov June 15, 2018, 12:47 a.m. | #1
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.
Masahiro Yamada June 26, 2018, 3:44 a.m. | #2
Hi Alexei,


2018-06-15 9:47 GMT+09:00 Alexei Starovoitov <alexei.starovoitov@gmail.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.



Sorry for the late reply.

Unfortunately, I will be busy for a while.

I will come back eventually
to check it out, but I cannot tell when.


Somebody else sent a patch equivalent to 1/3, so it is fine.

3/3 can go independently, so it will send it as a separate patch for now.





-- 
Best Regards
Masahiro Yamada
Janne Karhunen Jan. 31, 2019, 10:48 a.m. | #3
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.

>

>
Janne Karhunen Jan. 31, 2019, 11:09 a.m. | #4
Hi,

Never mind, not enough coffee for the morning. Looks good addressing
wise, but something goes haywire with the copy. Some size limitation?

[   84.402647] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.10.2-1ubuntu1 04/01/2014
[   84.403899] RIP: 0010:__memcpy+0x12/0x20
[   84.404441] Code: c1 e2 20 48 09 d0 48 31 c3 e9 76 ff ff ff 90 90
90 90 90 90 90 90 90 90 0f 1f 44 00 00 48 89 f8 48 89 d1 48 c1 e9 03
83 e2 07 <f3> 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 89 d1
f3 a4
[   84.407004] RSP: 0018:ffffc90000ac39c0 EFLAGS: 00010246
[   84.407714] RAX: ffff888041709000 RBX: 0000000000001000 RCX: 0000000000000200
[   84.408667] RDX: 0000000000000000 RSI: ffffffff82a7cb4d RDI: ffff888041709000
[   84.409668] RBP: ffffc90000ac3a08 R08: ffff888041709000 R09: 0000000000000000
[   84.410621] R10: 0000000000000000 R11: 000015fffefa3dbf R12: 0000000000001000
[   84.411710] R13: 0000000000001000 R14: ffffc90000ac3b28 R15: 0000000000001000
[   84.412675] FS:  00007f6cd3a35740(0000) GS:ffff88807da00000(0000)
knlGS:0000000000000000
[   84.413805] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   84.414655] CR2: ffffffff82a7cb4d CR3: 0000000031344000 CR4: 00000000000006f0
[   84.415656] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   84.416647] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   84.417619] Call Trace:
[   84.417996]  ? iov_iter_copy_from_user_atomic+0x21b/0x360
[   84.418754]  ? shmem_write_begin+0x4a/0x80
[   84.419396]  generic_perform_write+0xdd/0x1b0
[   84.419897]  __generic_file_write_iter+0x1ab/0x1d0
[   84.420453]  ? apparmor_file_alloc_security+0x4c/0x230
[   84.421082]  ? kmem_cache_alloc+0x1b5/0x1d0
[   84.421677]  generic_file_write_iter+0xb3/0x150
[   84.422353]  __vfs_write+0x145/0x1d0
[   84.422907]  vfs_write+0xae/0x1a0
[   84.423435]  kernel_write+0x55/0x70
[   84.423996]  fork_usermode_blob+0x85/0x11b
..

ret = fork_usermode_blob(&test_umh_start,
&test_umh_end - &test_umh_start, &um_info);

Addresses indeed seem ok and the '-fpic -fpie -fPIE -static' compiled
user mode blob sits in between those symbols correctly. Hummm ?


--
Janne

On Thu, Jan 31, 2019 at 12:48 PM Janne Karhunen
<janne.karhunen@gmail.com> wrote:
>

> 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.

> >

> >
Janne Karhunen Jan. 31, 2019, 12:40 p.m. | #5
Hi,

Okay my bad, proper __initconst declarations would do the trick, cool stuff.


--
Janne

On Thu, Jan 31, 2019 at 1:09 PM Janne Karhunen <janne.karhunen@gmail.com> wrote:
>

> Hi,

>

> Never mind, not enough coffee for the morning. Looks good addressing

> wise, but something goes haywire with the copy. Some size limitation?

>

> [   84.402647] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),

> BIOS 1.10.2-1ubuntu1 04/01/2014

> [   84.403899] RIP: 0010:__memcpy+0x12/0x20

> [   84.404441] Code: c1 e2 20 48 09 d0 48 31 c3 e9 76 ff ff ff 90 90

> 90 90 90 90 90 90 90 90 0f 1f 44 00 00 48 89 f8 48 89 d1 48 c1 e9 03

> 83 e2 07 <f3> 48 a5 89 d1 f3 a4 c3 66 0f 1f 44 00 00 48 89 f8 48 89 d1

> f3 a4

> [   84.407004] RSP: 0018:ffffc90000ac39c0 EFLAGS: 00010246

> [   84.407714] RAX: ffff888041709000 RBX: 0000000000001000 RCX: 0000000000000200

> [   84.408667] RDX: 0000000000000000 RSI: ffffffff82a7cb4d RDI: ffff888041709000

> [   84.409668] RBP: ffffc90000ac3a08 R08: ffff888041709000 R09: 0000000000000000

> [   84.410621] R10: 0000000000000000 R11: 000015fffefa3dbf R12: 0000000000001000

> [   84.411710] R13: 0000000000001000 R14: ffffc90000ac3b28 R15: 0000000000001000

> [   84.412675] FS:  00007f6cd3a35740(0000) GS:ffff88807da00000(0000)

> knlGS:0000000000000000

> [   84.413805] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033

> [   84.414655] CR2: ffffffff82a7cb4d CR3: 0000000031344000 CR4: 00000000000006f0

> [   84.415656] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

> [   84.416647] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

> [   84.417619] Call Trace:

> [   84.417996]  ? iov_iter_copy_from_user_atomic+0x21b/0x360

> [   84.418754]  ? shmem_write_begin+0x4a/0x80

> [   84.419396]  generic_perform_write+0xdd/0x1b0

> [   84.419897]  __generic_file_write_iter+0x1ab/0x1d0

> [   84.420453]  ? apparmor_file_alloc_security+0x4c/0x230

> [   84.421082]  ? kmem_cache_alloc+0x1b5/0x1d0

> [   84.421677]  generic_file_write_iter+0xb3/0x150

> [   84.422353]  __vfs_write+0x145/0x1d0

> [   84.422907]  vfs_write+0xae/0x1a0

> [   84.423435]  kernel_write+0x55/0x70

> [   84.423996]  fork_usermode_blob+0x85/0x11b

> ..

>

> ret = fork_usermode_blob(&test_umh_start,

> &test_umh_end - &test_umh_start, &um_info);

>

> Addresses indeed seem ok and the '-fpic -fpie -fPIE -static' compiled

> user mode blob sits in between those symbols correctly. Hummm ?

>

>

> --

> Janne

>

> On Thu, Jan 31, 2019 at 12:48 PM Janne Karhunen

> <janne.karhunen@gmail.com> wrote:

> >

> > 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.

> > >

> > >

Patch

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: