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* [PATCH bpf v1 0/3] fix BTF usage on embedded systems
@ 2020-09-20  5:01 Tony Ambardar
  2020-09-20  5:01 ` [PATCH bpf v1 1/3] bpf: fix sysfs export of empty BTF section Tony Ambardar
                   ` (4 more replies)
  0 siblings, 5 replies; 10+ messages in thread
From: Tony Ambardar @ 2020-09-20  5:01 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann
  Cc: Tony Ambardar, netdev, bpf, linux-arch, Arnd Bergmann

Hello,

I've been experimenting with BPF and BTF on small, emebedded platforms
requiring cross-compilation to varying archs, word-sizes, and endianness.
These environments are not the most common for the majority of eBPF users,
and have exposed multiple problems with basic functionality. This patch
series addresses some of these issues.

Enabling BTF support in the kernel can sometimes result in sysfs export
of /sys/kernel/btf/vmlinux as a zero-length file, which is still readable
and seen to leak non-zero kernel data. Patch #1 adds a sanity-check to
avoid this situation.

Small systems commonly enable LD_DEAD_CODE_DATA_ELIMINATION, which causes
the .BTF section data to be incorrectly removed and can trigger the problem
above. Patch #2 preserves the BTF data.

Even if BTF data is generated and embedded in the kernel, it may be encoded
as non-native endianness due to another bug [1] currently being worked on.
Patch #3 lets bpftool recognize the wrong BTF endianness rather than output
a confusing/misleading ELF header error message.

Patches #1 and #2 were first developed for Linux 5.4.x and should be
backported if possible. Feedback and suggestions for improvement are
welcome!

Thanks,
Tony

[1] https://lore.kernel.org/bpf/CAPGftE8ipAacAnm9xMHFabXCL-XrCXGmOsX-Nsjvz9wnh3Zx-w@mail.gmail.com/

Tony Ambardar (3):
  bpf: fix sysfs export of empty BTF section
  bpf: prevent .BTF section elimination
  libbpf: fix native endian assumption when parsing BTF

 include/asm-generic/vmlinux.lds.h | 2 +-
 kernel/bpf/sysfs_btf.c            | 6 +++---
 tools/lib/bpf/btf.c               | 6 ++++++
 3 files changed, 10 insertions(+), 4 deletions(-)

-- 
2.25.1


^ permalink raw reply	[flat|nested] 10+ messages in thread
* [PATCH bpf v1 1/3] bpf: fix sysfs export of empty BTF section
  2020-09-20  5:01 [PATCH bpf v1 0/3] fix BTF usage on embedded systems Tony Ambardar
@ 2020-09-20  5:01 ` Tony Ambardar
  2020-09-21 15:44   ` John Fastabend
  2020-09-21 19:21   ` Andrii Nakryiko
  2020-09-20  5:01 ` [PATCH bpf v1 2/3] bpf: prevent .BTF section elimination Tony Ambardar
                   ` (3 subsequent siblings)
  4 siblings, 2 replies; 10+ messages in thread
From: Tony Ambardar @ 2020-09-20  5:01 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann
  Cc: Tony Ambardar, netdev, bpf, linux-arch, Arnd Bergmann

If BTF data is missing or removed from the ELF section it is still exported
via sysfs as a zero-length file:

  root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux
  -r--r--r--    1 root    root    0 Jul 18 02:59 /sys/kernel/btf/vmlinux

Moreover, reads from this file succeed and leak kernel data:

  root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10
  000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
  *
  000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................|
  000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
  000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.|
  000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
  *
  002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................|
  002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....|
  002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`|

This situation was first observed with kernel 5.4.x, cross-compiled for a
MIPS target system. Fix by adding a sanity-check for export of zero-length
data sections.

Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs")

Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
---
 kernel/bpf/sysfs_btf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
index 3b495773de5a..11b3380887fa 100644
--- a/kernel/bpf/sysfs_btf.c
+++ b/kernel/bpf/sysfs_btf.c
@@ -30,15 +30,15 @@ static struct kobject *btf_kobj;
 
 static int __init btf_vmlinux_init(void)
 {
-	if (!__start_BTF)
+	bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
+
+	if (!__start_BTF || bin_attr_btf_vmlinux.size == 0)
 		return 0;
 
 	btf_kobj = kobject_create_and_add("btf", kernel_kobj);
 	if (!btf_kobj)
 		return -ENOMEM;
 
-	bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
-
 	return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
 }
 
-- 
2.25.1


^ permalink raw reply related	[flat|nested] 10+ messages in thread
* [PATCH bpf v1 2/3] bpf: prevent .BTF section elimination
  2020-09-20  5:01 [PATCH bpf v1 0/3] fix BTF usage on embedded systems Tony Ambardar
  2020-09-20  5:01 ` [PATCH bpf v1 1/3] bpf: fix sysfs export of empty BTF section Tony Ambardar
@ 2020-09-20  5:01 ` Tony Ambardar
  2020-09-21 15:45   ` John Fastabend
  2020-09-20  5:01 ` [PATCH bpf v1 3/3] libbpf: fix native endian assumption when parsing BTF Tony Ambardar
                   ` (2 subsequent siblings)
  4 siblings, 1 reply; 10+ messages in thread
From: Tony Ambardar @ 2020-09-20  5:01 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann
  Cc: Tony Ambardar, netdev, bpf, linux-arch, Arnd Bergmann

Systems with memory or disk constraints often reduce the kernel footprint
by configuring LD_DEAD_CODE_DATA_ELIMINATION. However, this can result in
removal of any BTF information.

Use the KEEP() macro to preserve the BTF data as done with other important
sections, while still allowing for smaller kernels.

Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")

Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
---
 include/asm-generic/vmlinux.lds.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 5430febd34be..7636bc71c71f 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -661,7 +661,7 @@
 #define BTF								\
 	.BTF : AT(ADDR(.BTF) - LOAD_OFFSET) {				\
 		__start_BTF = .;					\
-		*(.BTF)							\
+		KEEP(*(.BTF))						\
 		__stop_BTF = .;						\
 	}								\
 	. = ALIGN(4);							\
-- 
2.25.1


^ permalink raw reply related	[flat|nested] 10+ messages in thread
* [PATCH bpf v1 3/3] libbpf: fix native endian assumption when parsing BTF
  2020-09-20  5:01 [PATCH bpf v1 0/3] fix BTF usage on embedded systems Tony Ambardar
  2020-09-20  5:01 ` [PATCH bpf v1 1/3] bpf: fix sysfs export of empty BTF section Tony Ambardar
  2020-09-20  5:01 ` [PATCH bpf v1 2/3] bpf: prevent .BTF section elimination Tony Ambardar
@ 2020-09-20  5:01 ` Tony Ambardar
  2020-09-21 15:46   ` John Fastabend
  2020-09-21 19:24 ` [PATCH bpf v1 0/3] fix BTF usage on embedded systems Andrii Nakryiko
  2020-09-21 20:52 ` Daniel Borkmann
  4 siblings, 1 reply; 10+ messages in thread
From: Tony Ambardar @ 2020-09-20  5:01 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann
  Cc: Tony Ambardar, netdev, bpf, linux-arch, Arnd Bergmann

Code in btf__parse_raw() fails to detect raw BTF of non-native endianness
and assumes it must be ELF data, which then fails to parse as ELF and
yields a misleading error message:

  root:/# bpftool btf dump file /sys/kernel/btf/vmlinux
  libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux

For example, this could occur after cross-compiling a BTF-enabled kernel
for a target with non-native endianness, which is currently unsupported.

Check for correct endianness and emit a clearer error message:

  root:/# bpftool btf dump file /sys/kernel/btf/vmlinux
  libbpf: non-native BTF endianness is not supported

Fixes: 94a1fedd63ed ("libbpf: Add btf__parse_raw() and generic btf__parse() APIs")

Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
---
 tools/lib/bpf/btf.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 7dfca7016aaa..6bdbc389b493 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -659,6 +659,12 @@ struct btf *btf__parse_raw(const char *path)
 		err = -EIO;
 		goto err_out;
 	}
+	if (magic == __bswap_16(BTF_MAGIC)) {
+		/* non-native endian raw BTF */
+		pr_warn("non-native BTF endianness is not supported\n");
+		err = -LIBBPF_ERRNO__ENDIAN;
+		goto err_out;
+	}
 	if (magic != BTF_MAGIC) {
 		/* definitely not a raw BTF */
 		err = -EPROTO;
-- 
2.25.1


^ permalink raw reply related	[flat|nested] 10+ messages in thread
* RE: [PATCH bpf v1 1/3] bpf: fix sysfs export of empty BTF section
  2020-09-20  5:01 ` [PATCH bpf v1 1/3] bpf: fix sysfs export of empty BTF section Tony Ambardar
@ 2020-09-21 15:44   ` John Fastabend
  2020-09-21 19:21   ` Andrii Nakryiko
  1 sibling, 0 replies; 10+ messages in thread
From: John Fastabend @ 2020-09-21 15:44 UTC (permalink / raw)
  To: Tony Ambardar, Alexei Starovoitov, Daniel Borkmann
  Cc: Tony Ambardar, netdev, bpf, linux-arch, Arnd Bergmann

Tony Ambardar wrote:
> If BTF data is missing or removed from the ELF section it is still exported
> via sysfs as a zero-length file:
> 
>   root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux
>   -r--r--r--    1 root    root    0 Jul 18 02:59 /sys/kernel/btf/vmlinux
> 
> Moreover, reads from this file succeed and leak kernel data:
> 
>   root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10
>   000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>   *
>   000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................|
>   000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>   000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.|
>   000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>   *
>   002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................|
>   002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....|
>   002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`|
> 
> This situation was first observed with kernel 5.4.x, cross-compiled for a
> MIPS target system. Fix by adding a sanity-check for export of zero-length
> data sections.
> 
> Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs")
> 
> Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
> ---
>  kernel/bpf/sysfs_btf.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index 3b495773de5a..11b3380887fa 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c
> @@ -30,15 +30,15 @@ static struct kobject *btf_kobj;
>  
>  static int __init btf_vmlinux_init(void)
>  {
> -	if (!__start_BTF)
> +	bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> +
> +	if (!__start_BTF || bin_attr_btf_vmlinux.size == 0)
>  		return 0;
>  
>  	btf_kobj = kobject_create_and_add("btf", kernel_kobj);
>  	if (!btf_kobj)
>  		return -ENOMEM;
>  
> -	bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> -
>  	return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
>  }

Thanks LGTM.

Acked-by: John Fastabend <john.fastabend@gmail.com>

^ permalink raw reply	[flat|nested] 10+ messages in thread
* RE: [PATCH bpf v1 2/3] bpf: prevent .BTF section elimination
  2020-09-20  5:01 ` [PATCH bpf v1 2/3] bpf: prevent .BTF section elimination Tony Ambardar
@ 2020-09-21 15:45   ` John Fastabend
  0 siblings, 0 replies; 10+ messages in thread
From: John Fastabend @ 2020-09-21 15:45 UTC (permalink / raw)
  To: Tony Ambardar, Alexei Starovoitov, Daniel Borkmann
  Cc: Tony Ambardar, netdev, bpf, linux-arch, Arnd Bergmann

Tony Ambardar wrote:
> Systems with memory or disk constraints often reduce the kernel footprint
> by configuring LD_DEAD_CODE_DATA_ELIMINATION. However, this can result in
> removal of any BTF information.
> 
> Use the KEEP() macro to preserve the BTF data as done with other important
> sections, while still allowing for smaller kernels.
> 
> Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
> 
> Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
> ---
>  include/asm-generic/vmlinux.lds.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 5430febd34be..7636bc71c71f 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -661,7 +661,7 @@
>  #define BTF								\
>  	.BTF : AT(ADDR(.BTF) - LOAD_OFFSET) {				\
>  		__start_BTF = .;					\
> -		*(.BTF)							\
> +		KEEP(*(.BTF))						\
>  		__stop_BTF = .;						\
>  	}								\
>  	. = ALIGN(4);							\
> -- 
> 2.25.1
> 

Acked-by: John Fastabend <john.fastabend@gmail.com>

^ permalink raw reply	[flat|nested] 10+ messages in thread
* RE: [PATCH bpf v1 3/3] libbpf: fix native endian assumption when parsing BTF
  2020-09-20  5:01 ` [PATCH bpf v1 3/3] libbpf: fix native endian assumption when parsing BTF Tony Ambardar
@ 2020-09-21 15:46   ` John Fastabend
  0 siblings, 0 replies; 10+ messages in thread
From: John Fastabend @ 2020-09-21 15:46 UTC (permalink / raw)
  To: Tony Ambardar, Alexei Starovoitov, Daniel Borkmann
  Cc: Tony Ambardar, netdev, bpf, linux-arch, Arnd Bergmann

Tony Ambardar wrote:
> Code in btf__parse_raw() fails to detect raw BTF of non-native endianness
> and assumes it must be ELF data, which then fails to parse as ELF and
> yields a misleading error message:
> 
>   root:/# bpftool btf dump file /sys/kernel/btf/vmlinux
>   libbpf: failed to get EHDR from /sys/kernel/btf/vmlinux
> 
> For example, this could occur after cross-compiling a BTF-enabled kernel
> for a target with non-native endianness, which is currently unsupported.
> 
> Check for correct endianness and emit a clearer error message:
> 
>   root:/# bpftool btf dump file /sys/kernel/btf/vmlinux
>   libbpf: non-native BTF endianness is not supported
> 
> Fixes: 94a1fedd63ed ("libbpf: Add btf__parse_raw() and generic btf__parse() APIs")
> 
> Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
> ---
>  tools/lib/bpf/btf.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 7dfca7016aaa..6bdbc389b493 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -659,6 +659,12 @@ struct btf *btf__parse_raw(const char *path)
>  		err = -EIO;
>  		goto err_out;
>  	}
> +	if (magic == __bswap_16(BTF_MAGIC)) {
> +		/* non-native endian raw BTF */
> +		pr_warn("non-native BTF endianness is not supported\n");
> +		err = -LIBBPF_ERRNO__ENDIAN;
> +		goto err_out;
> +	}
>  	if (magic != BTF_MAGIC) {
>  		/* definitely not a raw BTF */
>  		err = -EPROTO;
> -- 
> 2.25.1
> 

Acked-by: John Fastabend <john.fastabend@gmail.com>

^ permalink raw reply	[flat|nested] 10+ messages in thread
* Re: [PATCH bpf v1 1/3] bpf: fix sysfs export of empty BTF section
  2020-09-20  5:01 ` [PATCH bpf v1 1/3] bpf: fix sysfs export of empty BTF section Tony Ambardar
  2020-09-21 15:44   ` John Fastabend
@ 2020-09-21 19:21   ` Andrii Nakryiko
  1 sibling, 0 replies; 10+ messages in thread
From: Andrii Nakryiko @ 2020-09-21 19:21 UTC (permalink / raw)
  To: Tony Ambardar
  Cc: Alexei Starovoitov, Daniel Borkmann, Networking, bpf, linux-arch,
	Arnd Bergmann

On Sat, Sep 19, 2020 at 10:05 PM Tony Ambardar <tony.ambardar@gmail.com> wrote:
>
> If BTF data is missing or removed from the ELF section it is still exported
> via sysfs as a zero-length file:
>
>   root@OpenWrt:/# ls -l /sys/kernel/btf/vmlinux
>   -r--r--r--    1 root    root    0 Jul 18 02:59 /sys/kernel/btf/vmlinux
>
> Moreover, reads from this file succeed and leak kernel data:
>
>   root@OpenWrt:/# hexdump -C /sys/kernel/btf/vmlinux|head -10
>   000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>   *
>   000cc0 00 00 00 00 00 00 00 00 00 00 00 00 80 83 b0 80 |................|
>   000cd0 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>   000ce0 00 00 00 00 00 00 00 00 00 00 00 00 57 ac 6e 9d |............W.n.|
>   000cf0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
>   *
>   002650 00 00 00 00 00 00 00 10 00 00 00 01 00 00 00 01 |................|
>   002660 80 82 9a c4 80 85 97 80 81 a9 51 68 00 00 00 02 |..........Qh....|
>   002670 80 25 44 dc 80 85 97 80 81 a9 50 24 81 ab c4 60 |.%D.......P$...`|
>
> This situation was first observed with kernel 5.4.x, cross-compiled for a
> MIPS target system. Fix by adding a sanity-check for export of zero-length
> data sections.
>
> Fixes: 341dfcf8d78e ("btf: expose BTF info through sysfs")
>
> Signed-off-by: Tony Ambardar <Tony.Ambardar@gmail.com>
> ---

Apparently sysfs infrastructure doesn't validate read position and
size when bin_attribute's size is 0, and just expects read callback to
handle such situation explicitly. Preventing sysfs entry from
registering seems like a good solution. Thanks!

Acked-by: Andrii Nakryiko <andriin@fb.com>

>  kernel/bpf/sysfs_btf.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
> index 3b495773de5a..11b3380887fa 100644
> --- a/kernel/bpf/sysfs_btf.c
> +++ b/kernel/bpf/sysfs_btf.c
> @@ -30,15 +30,15 @@ static struct kobject *btf_kobj;
>
>  static int __init btf_vmlinux_init(void)
>  {
> -       if (!__start_BTF)
> +       bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> +
> +       if (!__start_BTF || bin_attr_btf_vmlinux.size == 0)
>                 return 0;
>
>         btf_kobj = kobject_create_and_add("btf", kernel_kobj);
>         if (!btf_kobj)
>                 return -ENOMEM;
>
> -       bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
> -
>         return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
>  }
>
> --
> 2.25.1
>

^ permalink raw reply	[flat|nested] 10+ messages in thread
* Re: [PATCH bpf v1 0/3] fix BTF usage on embedded systems
  2020-09-20  5:01 [PATCH bpf v1 0/3] fix BTF usage on embedded systems Tony Ambardar
                   ` (2 preceding siblings ...)
  2020-09-20  5:01 ` [PATCH bpf v1 3/3] libbpf: fix native endian assumption when parsing BTF Tony Ambardar
@ 2020-09-21 19:24 ` Andrii Nakryiko
  2020-09-21 20:52 ` Daniel Borkmann
  4 siblings, 0 replies; 10+ messages in thread
From: Andrii Nakryiko @ 2020-09-21 19:24 UTC (permalink / raw)
  To: Tony Ambardar
  Cc: Alexei Starovoitov, Daniel Borkmann, Networking, bpf, linux-arch,
	Arnd Bergmann

On Sat, Sep 19, 2020 at 10:03 PM Tony Ambardar <tony.ambardar@gmail.com> wrote:
>
> Hello,
>
> I've been experimenting with BPF and BTF on small, emebedded platforms
> requiring cross-compilation to varying archs, word-sizes, and endianness.
> These environments are not the most common for the majority of eBPF users,
> and have exposed multiple problems with basic functionality. This patch
> series addresses some of these issues.
>
> Enabling BTF support in the kernel can sometimes result in sysfs export
> of /sys/kernel/btf/vmlinux as a zero-length file, which is still readable
> and seen to leak non-zero kernel data. Patch #1 adds a sanity-check to
> avoid this situation.
>
> Small systems commonly enable LD_DEAD_CODE_DATA_ELIMINATION, which causes
> the .BTF section data to be incorrectly removed and can trigger the problem
> above. Patch #2 preserves the BTF data.
>
> Even if BTF data is generated and embedded in the kernel, it may be encoded
> as non-native endianness due to another bug [1] currently being worked on.
> Patch #3 lets bpftool recognize the wrong BTF endianness rather than output
> a confusing/misleading ELF header error message.
>
> Patches #1 and #2 were first developed for Linux 5.4.x and should be
> backported if possible. Feedback and suggestions for improvement are
> welcome!
>
> Thanks,
> Tony
>
> [1] https://lore.kernel.org/bpf/CAPGftE8ipAacAnm9xMHFabXCL-XrCXGmOsX-Nsjvz9wnh3Zx-w@mail.gmail.com/
>
> Tony Ambardar (3):
>   bpf: fix sysfs export of empty BTF section
>   bpf: prevent .BTF section elimination
>   libbpf: fix native endian assumption when parsing BTF
>
>  include/asm-generic/vmlinux.lds.h | 2 +-
>  kernel/bpf/sysfs_btf.c            | 6 +++---
>  tools/lib/bpf/btf.c               | 6 ++++++
>  3 files changed, 10 insertions(+), 4 deletions(-)
>
> --
> 2.25.1
>

All fixes look good:

Acked-by: Andrii Nakryiko <andriin@fb.com>

^ permalink raw reply	[flat|nested] 10+ messages in thread
* Re: [PATCH bpf v1 0/3] fix BTF usage on embedded systems
  2020-09-20  5:01 [PATCH bpf v1 0/3] fix BTF usage on embedded systems Tony Ambardar
                   ` (3 preceding siblings ...)
  2020-09-21 19:24 ` [PATCH bpf v1 0/3] fix BTF usage on embedded systems Andrii Nakryiko
@ 2020-09-21 20:52 ` Daniel Borkmann
  4 siblings, 0 replies; 10+ messages in thread
From: Daniel Borkmann @ 2020-09-21 20:52 UTC (permalink / raw)
  To: Tony Ambardar, Alexei Starovoitov; +Cc: netdev, bpf, linux-arch, Arnd Bergmann

On 9/20/20 7:01 AM, Tony Ambardar wrote:
> Hello,
> 
> I've been experimenting with BPF and BTF on small, emebedded platforms
> requiring cross-compilation to varying archs, word-sizes, and endianness.
> These environments are not the most common for the majority of eBPF users,
> and have exposed multiple problems with basic functionality. This patch
> series addresses some of these issues.
> 
> Enabling BTF support in the kernel can sometimes result in sysfs export
> of /sys/kernel/btf/vmlinux as a zero-length file, which is still readable
> and seen to leak non-zero kernel data. Patch #1 adds a sanity-check to
> avoid this situation.
> 
> Small systems commonly enable LD_DEAD_CODE_DATA_ELIMINATION, which causes
> the .BTF section data to be incorrectly removed and can trigger the problem
> above. Patch #2 preserves the BTF data.
> 
> Even if BTF data is generated and embedded in the kernel, it may be encoded
> as non-native endianness due to another bug [1] currently being worked on.
> Patch #3 lets bpftool recognize the wrong BTF endianness rather than output
> a confusing/misleading ELF header error message.
> 
> Patches #1 and #2 were first developed for Linux 5.4.x and should be
> backported if possible. Feedback and suggestions for improvement are
> welcome!
> 
> Thanks,
> Tony
> 
> [1] https://lore.kernel.org/bpf/CAPGftE8ipAacAnm9xMHFabXCL-XrCXGmOsX-Nsjvz9wnh3Zx-w@mail.gmail.com/
> 
> Tony Ambardar (3):
>    bpf: fix sysfs export of empty BTF section
>    bpf: prevent .BTF section elimination
>    libbpf: fix native endian assumption when parsing BTF
> 
>   include/asm-generic/vmlinux.lds.h | 2 +-
>   kernel/bpf/sysfs_btf.c            | 6 +++---
>   tools/lib/bpf/btf.c               | 6 ++++++
>   3 files changed, 10 insertions(+), 4 deletions(-)
> 

Applied, thanks!

^ permalink raw reply	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2020-09-21 21:16 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-20  5:01 [PATCH bpf v1 0/3] fix BTF usage on embedded systems Tony Ambardar
2020-09-20  5:01 ` [PATCH bpf v1 1/3] bpf: fix sysfs export of empty BTF section Tony Ambardar
2020-09-21 15:44   ` John Fastabend
2020-09-21 19:21   ` Andrii Nakryiko
2020-09-20  5:01 ` [PATCH bpf v1 2/3] bpf: prevent .BTF section elimination Tony Ambardar
2020-09-21 15:45   ` John Fastabend
2020-09-20  5:01 ` [PATCH bpf v1 3/3] libbpf: fix native endian assumption when parsing BTF Tony Ambardar
2020-09-21 15:46   ` John Fastabend
2020-09-21 19:24 ` [PATCH bpf v1 0/3] fix BTF usage on embedded systems Andrii Nakryiko
2020-09-21 20:52 ` Daniel Borkmann

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