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3 Commits

Author SHA1 Message Date
Tony Ambardar 9fe6283a1d bpf: Fix sysfs export of empty BTF section 
commit e23bb04b0c938588eae41b7f4712b722290ed2b8 upstream.

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>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/b38db205a66238f70823039a8c531535864eaac5.1600417359.git.Tony.Ambardar@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 2021-03-16 16:37:55 +08:00
Fangrui Song 66aed5f2e4 bpf: Support llvm-objcopy for vmlinux BTF 
commit 90ceddcb495008ac8ba7a3dce297841efcd7d584 upstream.

Simplify gen_btf logic to make it work with llvm-objcopy. The existing
'file format' and 'architecture' parsing logic is brittle and does not
work with llvm-objcopy/llvm-objdump.

'file format' output of llvm-objdump>=11 will match GNU objdump, but
'architecture' (bfdarch) may not.

.BTF in .tmp_vmlinux.btf is non-SHF_ALLOC. Add the SHF_ALLOC flag
because it is part of vmlinux image used for introspection. C code
can reference the section via linker script defined __start_BTF and
__stop_BTF. This fixes a small problem that previous .BTF had the
SHF_WRITE flag (objcopy -I binary -O elf* synthesized .data).

Additionally, `objcopy -I binary` synthesized symbols
_binary__btf_vmlinux_bin_start and _binary__btf_vmlinux_bin_stop (not
used elsewhere) are replaced with more commonplace __start_BTF and
__stop_BTF.

Add 2>/dev/null because GNU objcopy (but not llvm-objcopy) warns
"empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?"

We use a dd command to change the e_type field in the ELF header from
ET_EXEC to ET_REL so that lld will accept .btf.vmlinux.bin.o.  Accepting
ET_EXEC as an input file is an extremely rare GNU ld feature that lld
does not intend to support, because this is error-prone.

The output section description .BTF in include/asm-generic/vmlinux.lds.h
avoids potential subtle orphan section placement issues and suppresses
--orphan-handling=warn warnings.

Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux")
Fixes: cb0cc635c7a9 ("powerpc: Include .BTF section")
Reported-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Fangrui Song <maskray@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Stanislav Fomichev <sdf@google.com>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Link: https://github.com/ClangBuiltLinux/linux/issues/871
Link: https://lore.kernel.org/bpf/20200318222746.173648-1-maskray@google.com
Signed-off-by: Maria Teguiani <teguiani@google.com>
Tested-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 2021-03-16 16:28:55 +08:00
Kaixu Xia 590eaf1fec Init Repo base on linux 5.4.32 long term, and add base tlinux kernel interfaces. 
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
 2021-03-16 11:01:34 +08:00