Lets clean up bpf_dbg a bit and improve its code slightly
in various areas: i) Get rid of some macros as there's no
good reason for keeping them, ii) remove one unused variable
and reduce scope of various variables found by cppcheck,
iii) Close non-default file descriptors when exiting the shell.
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Valgrind found that extracted labels that are passed from the lexer
weren't freed upon exit. Therefore, add a small helper function that
walks label tables and frees them. Since also NULL can be passed to
free(3), we do not need to take care of that here. While at it, fix
up a spacing error in bpf_set_curr_label().
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
We must not leave the socket intact in bpf_runnable(). The socket
is used to test if the filter code is being accepted by the kernel
or not. So right after we do the setsockopt(2), we need to close
it again.
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
There are a couple of valid use cases for a minimal low-level bpf asm
like tool, for example, using/linking to libpcap is not an option, the
required BPF filters use Linux extensions that are not supported by
libpcap's compiler, a filter might be more complex and not cleanly
implementable with libpcap's compiler, particular filter codes should
be optimized differently than libpcap's internal BPF compiler does,
or for security audits of emitted BPF JIT code for prepared set of BPF
instructions resp. BPF JIT compiler development in general.
Then, in such cases writing such a filter in low-level syntax can be
an good alternative, for example, xt_bpf and cls_bpf users might have
requirements that could result in more complex filter code, or one that
cannot be expressed with libpcap (e.g. different return codes in
cls_bpf for flowids on various BPF code paths).
Moreover, BPF JIT implementors may wish to manually write test cases
in order to verify the resulting JIT image, and thus need low-level
access to BPF code generation as well. Therefore, complete the available
toolchain for BPF with this small bpf_asm helper tool for the tools/net/
directory. These 3 complementary minimal helper tools round up and
facilitate BPF development.
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch adds a minimal BPF debugger that "emulates" the kernel's
BPF engine (w/o extensions) and allows for single stepping (forwards
and backwards through BPF code) or running with >=1 breakpoints through
selected or all packets from a pcap file with a provided user filter
in order to facilitate verification of a BPF program. When a breakpoint
is being hit, it dumps all register contents, decoded instructions and
in case of branches both decoded branch targets as well as other useful
information.
Having this facility is in particular useful to verify BPF programs
against given test traffic *before* attaching to a live system.
With the general availability of cls_bpf, xt_bpf, socket filters,
team driver and e.g. PTP code, all BPF users, quite often a single
more complex BPF program is being used. Reasons for a more complex
BPF program are primarily to optimize execution time for making a
verdict when multiple simple BPF programs are combined into one in
order to prevent parsing same headers multiple times. In particular,
for cls_bpf that can have various return paths for encoding flowids,
and xt_bpf to come to a fw verdict this can be the case.
Therefore, as this can result in more complex and harder to debug
code, it would be very useful to have this minimal tool for testing
purposes. It can also be of help for BPF JIT developers as filters
are "test attached" to the kernel on a temporary socket thus
triggering a JIT image dump when enabled. The tool uses an interactive
libreadline shell with auto-completion and history support.
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This is a minimal stand-alone user space helper, that allows for debugging or
verification of emitted BPF JIT images. This is in particular useful for
emitted opcode debugging, since minor bugs in the JIT compiler can be fatal.
The disassembler is architecture generic and uses libopcodes and libbfd.
How to get to the disassembly, example:
1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
3) Run e.g. `bpf_jit_disasm -o` to disassemble the most recent JIT code output
`bpf_jit_disasm -o` will display the related opcodes to a particular instruction
as well. Example for x86_64:
$ ./bpf_jit_disasm
94 bytes emitted from JIT compiler (pass:3, flen:9)
ffffffffa0356000 + <x>:
0: push %rbp
1: mov %rsp,%rbp
4: sub $0x60,%rsp
8: mov %rbx,-0x8(%rbp)
c: mov 0x68(%rdi),%r9d
10: sub 0x6c(%rdi),%r9d
14: mov 0xe0(%rdi),%r8
1b: mov $0xc,%esi
20: callq 0xffffffffe0d01b71
25: cmp $0x86dd,%eax
2a: jne 0x000000000000003d
2c: mov $0x14,%esi
31: callq 0xffffffffe0d01b8d
36: cmp $0x6,%eax
[...]
5c: leaveq
5d: retq
$ ./bpf_jit_disasm -o
94 bytes emitted from JIT compiler (pass:3, flen:9)
ffffffffa0356000 + <x>:
0: push %rbp
55
1: mov %rsp,%rbp
48 89 e5
4: sub $0x60,%rsp
48 83 ec 60
8: mov %rbx,-0x8(%rbp)
48 89 5d f8
c: mov 0x68(%rdi),%r9d
44 8b 4f 68
10: sub 0x6c(%rdi),%r9d
44 2b 4f 6c
[...]
5c: leaveq
c9
5d: retq
c3
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
