This patch set proposes the addition of a new way for performing type queries to
BPF. It introduces the "type matches" relation, similar to what is already
present with "type exists" (in the form of bpf_core_type_exists).
"type exists" performs fairly superficial checking, mostly concerned with
whether a type exists in the kernel and is of the same kind (enum/struct/...).
Notably, compatibility checks for members of composite types is lacking.
The newly introduced "type matches" (bpf_core_type_matches) fills this gap in
that it performs stricter checks: compatibility of members and existence of
similarly named enum variants is checked as well. E.g., given these definitions:
struct task_struct___og { int pid; int tgid; };
struct task_struct___foo { int foo; }
'task_struct___og' would "match" the kernel type 'task_struct', because the
members match up, while 'task_struct___foo' would not match, because the
kernel's 'task_struct' has no member named 'foo'.
More precisely, the "type match" relation is defined as follows (copied from
source):
- modifiers and typedefs are stripped (and, hence, effectively ignored)
- generally speaking types need to be of same kind (struct vs. struct, union
vs. union, etc.)
- exceptions are struct/union behind a pointer which could also match a
forward declaration of a struct or union, respectively, and enum vs.
enum64 (see below)
Then, depending on type:
- integers:
- match if size and signedness match
- arrays & pointers:
- target types are recursively matched
- structs & unions:
- local members need to exist in target with the same name
- for each member we recursively check match unless it is already behind a
pointer, in which case we only check matching names and compatible kind
- enums:
- local variants have to have a match in target by symbolic name (but not
numeric value)
- size has to match (but enum may match enum64 and vice versa)
- function pointers:
- number and position of arguments in local type has to match target
- for each argument and the return value we recursively check match
Enabling this feature requires a new relocation to be made known to the
compiler. This is being taken care of for LLVM as part of
https://reviews.llvm.org/D126838.
If applied, among other things, usage of this functionality could have helped
flag issues such as the one discussed here
https://lore.kernel.org/all/93a20759600c05b6d9e4359a1517c88e06b44834.camel@xxxxxx/
earlier.
Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
Changelog:
v1 -> v2:
- deduplicated and moved core algorithm into relo_core.c
- adjusted bpf_core_names_match to get btf_type passed in
- removed some length equality checks before strncmp usage
- correctly use kflag from targ_t instead of local_t
- added comment for meaning of kflag w/ FWD kind
- __u32 -> u32
- handle BTF_KIND_FWD properly in bpftool marking logic
- rebased
Daniel Müller (9):
bpf: Introduce TYPE_MATCH related constants/macros
bpftool: Honor BPF_CORE_TYPE_MATCHES relocation
bpf: Introduce btf_int_bits() function
libbpf: Add type match support
bpf: Add type match support
libbpf: Honor TYPE_MATCH relocation
selftests/bpf: Add type-match checks to type-based tests
selftests/bpf: Add test checking more characteristics
selftests/bpf: Add nested type to type based tests
include/linux/btf.h | 5 +
include/uapi/linux/bpf.h | 1 +
kernel/bpf/btf.c | 9 +
tools/bpf/bpftool/gen.c | 107 +++++++
tools/include/uapi/linux/bpf.h | 1 +
tools/lib/bpf/bpf_core_read.h | 11 +
tools/lib/bpf/libbpf.c | 6 +
tools/lib/bpf/relo_core.c | 292 +++++++++++++++++-
tools/lib/bpf/relo_core.h | 4 +
.../selftests/bpf/prog_tests/core_reloc.c | 72 ++++-
.../progs/btf__core_reloc_type_based___diff.c | 3 +
.../selftests/bpf/progs/core_reloc_types.h | 107 ++++++-
.../bpf/progs/test_core_reloc_type_based.c | 44 ++-
13 files changed, 644 insertions(+), 18 deletions(-)
create mode 100644 tools/testing/selftests/bpf/progs/btf__core_reloc_type_based___diff.c
--
2.30.2
