Teach libbpf to post-process BPF verifier log on BPF program load
failure and detect known error patterns to provide user with more
context.
Currently there is one such common situation: an "unguarded" failed BPF
CO-RE relocation. While failing CO-RE relocation is expected, it is
expected to be property guarded in BPF code such that BPF verifier
always eliminates BPF instructions corresponding to such failed CO-RE
relos as dead code. In cases when user failed to take such precautions,
BPF verifier provides the best log it can:
123: (85) call unknown#195896080
invalid func unknown#195896080
Such incomprehensible log error is due to libbpf "poisoning" BPF
instruction that corresponds to failed CO-RE relocation by replacing it
with invalid `call 0xbad2310` instruction (195896080 == 0xbad2310 reads
"bad relo" if you squint hard enough).
Luckily, libbpf has all the necessary information to look up CO-RE
relocation that failed and provide more human-readable description of
what's going on:
5: <invalid CO-RE relocation>
failed to resolve CO-RE relocation <byte_off> [6] struct task_struct___bad.fake_field_subprog (0:2 @ offset 8)
This hopefully makes it much easier to understand what's wrong with
user's BPF program without googling magic constants.
This BPF verifier log fixup is setup to be extensible and is going to be
used for at least one other upcoming feature of libbpf in follow up patches.
Libbpf is parsing lines of BPF verifier log starting from the very end.
Currently it processes up to 10 lines of code looking for familiar
patterns. This avoids wasting lots of CPU processing huge verifier logs
(especially for log_level=2 verbosity level). Actual verification error
should normally be found in last few lines, so this should work
reliably.
If libbpf needs to expand log beyond available log_buf_size, it
truncates the end of the verifier log. Given verifier log normally ends
with something like:
processed 2 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
... truncating this on program load error isn't too bad (end user can
always increase log size, if it needs to get complete log).
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220426004511.2691730-10-andrii@kernel.org
Simplify bpf_core_parse_spec() signature to take struct bpf_core_relo as
an input instead of requiring callers to decompose them into type_id,
relo, spec_str, etc. This makes using and reusing this helper easier.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220426004511.2691730-9-andrii@kernel.org
Refactor how CO-RE relocation is formatted. Now it dumps human-readable
representation, currently used by libbpf in either debug or error
message output during CO-RE relocation resolution process, into provided
buffer. This approach allows for better reuse of this functionality
outside of CO-RE relocation resolution, which we'll use in next patch
for providing better error message for BPF verifier rejecting BPF
program due to unguarded failed CO-RE relocation.
It also gets rid of annoying "stitching" of libbpf_print() calls, which
was the only place where we did this.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220426004511.2691730-8-andrii@kernel.org
Use type name for checking whether CO-RE relocation is referring to
anonymous type. Using spec string makes no sense.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220426004511.2691730-2-andrii@kernel.org
BTFGen needs to run the core relocation logic in order to understand
what are the types involved in a given relocation.
Currently bpf_core_apply_relo() calculates and **applies** a relocation
to an instruction. Having both operations in the same function makes it
difficult to only calculate the relocation without patching the
instruction. This commit splits that logic in two different phases: (1)
calculate the relocation and (2) patch the instruction.
For the first phase bpf_core_apply_relo() is renamed to
bpf_core_calc_relo_insn() who is now only on charge of calculating the
relocation, the second phase uses the already existing
bpf_core_patch_insn(). bpf_object__relocate_core() uses both of them and
the BTFGen will use only bpf_core_calc_relo_insn().
Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
Signed-off-by: Rafael David Tinoco <rafael.tinoco@aquasec.com>
Signed-off-by: Lorenzo Fontana <lorenzo.fontana@elastic.co>
Signed-off-by: Leonardo Di Donato <leonardo.didonato@elastic.co>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220215225856.671072-2-mauricio@kinvolk.io
In case of BPF_CORE_TYPE_ID_LOCAL we fill out target result explicitly.
But targ_res itself isn't initialized in such a case, and subsequent
call to bpf_core_patch_insn() might read uninitialized field (like
fail_memsz_adjust in this case). So ensure that targ_res is
zero-initialized for BPF_CORE_TYPE_ID_LOCAL case.
This was reported by Coverity static analyzer.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20211214010032.3843804-1-andrii@kernel.org
During linking, type IDs in the resulting linked BPF object file can
change, and so ldimm64 instructions corresponding to
BPF_CORE_TYPE_ID_TARGET and BPF_CORE_TYPE_ID_LOCAL CO-RE relos can get
their imm value out of sync with actual CO-RE relocation information
that's updated by BPF linker properly during linking process.
We could teach BPF linker to adjust such instructions, but it feels
a bit too much for linker to re-implement good chunk of
bpf_core_patch_insns logic just for this. This is a redundant safety
check for TYPE_ID relocations, as the real validation is in matching
CO-RE specs, so if that works fine, it's very unlikely that there is
something wrong with the instruction itself.
So, instead, teach libbpf (and kernel) to ignore insn->imm for
BPF_CORE_TYPE_ID_TARGET and BPF_CORE_TYPE_ID_LOCAL relos.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211213010706.100231-1-andrii@kernel.org
enum bpf_core_relo_kind is generated by llvm and processed by libbpf.
It's a de-facto uapi.
With CO-RE in the kernel the bpf_core_relo_kind values become uapi de-jure.
Also rename them with BPF_CORE_ prefix to distinguish from conflicting names in
bpf_core_read.h. The enums bpf_field_info_kind, bpf_type_id_kind,
bpf_type_info_kind, bpf_enum_value_kind are passing different values from bpf
program into llvm.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211201181040.23337-5-alexei.starovoitov@gmail.com
Make relo_core.c to be compiled for the kernel and for user space libbpf.
Note the patch is reducing BPF_CORE_SPEC_MAX_LEN from 64 to 32.
This is the maximum number of nested structs and arrays.
For example:
struct sample {
int a;
struct {
int b[10];
};
};
struct sample *s = ...;
int *y = &s->b[5];
This field access is encoded as "0:1:0:5" and spec len is 4.
The follow up patch might bump it back to 64.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211201181040.23337-4-alexei.starovoitov@gmail.com
To prepare relo_core.c to be compiled in the kernel and the user space
replace btf__type_by_id with btf_type_by_id.
In libbpf btf__type_by_id and btf_type_by_id have different behavior.
bpf_core_apply_relo_insn() needs behavior of uapi btf__type_by_id
vs internal btf_type_by_id, but type_id range check is already done
in bpf_core_apply_relo(), so it's safe to replace it everywhere.
The kernel btf_type_by_id() does the check anyway. It doesn't hurt.
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211201181040.23337-2-alexei.starovoitov@gmail.com
Use the compiler-defined __BYTE_ORDER__ instead of the libc-defined
__BYTE_ORDER for consistency.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211026010831.748682-3-iii@linux.ibm.com
Move CO-RE logic into separate file.
The internal interface between libbpf and CO-RE is through
bpf_core_apply_relo_insn() function and few structs defined in relo_core.h.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210721000822.40958-5-alexei.starovoitov@gmail.com
