diff options
| author | Hao Luo <haoluo@google.com> | 2021-08-11 17:38:19 -0700 |
|---|---|---|
| committer | Andrii Nakryiko <andrii@kernel.org> | 2021-08-13 15:56:28 -0700 |
| commit | 2211c825e7b6b99bbcabab4e0130a2779275dcc3 (patch) | |
| tree | c2d65fe354da96b6f72b97aa4f95325d975d095b /tools/lib/bpf | |
| parent | cf7a5cba86fc2d3000c555b9568f7dd0f43bf0d4 (diff) | |
libbpf: Support weak typed ksyms.
Currently weak typeless ksyms have default value zero, when they don't
exist in the kernel. However, weak typed ksyms are rejected by libbpf
if they can not be resolved. This means that if a bpf object contains
the declaration of a nonexistent weak typed ksym, it will be rejected
even if there is no program that references the symbol.
Nonexistent weak typed ksyms can also default to zero just like
typeless ones. This allows programs that access weak typed ksyms to be
accepted by verifier, if the accesses are guarded. For example,
extern const int bpf_link_fops3 __ksym __weak;
/* then in BPF program */
if (&bpf_link_fops3) {
/* use bpf_link_fops3 */
}
If actual use of nonexistent typed ksym is not guarded properly,
verifier would see that register is not PTR_TO_BTF_ID and wouldn't
allow to use it for direct memory reads or passing it to BPF helpers.
Signed-off-by: Hao Luo <haoluo@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210812003819.2439037-1-haoluo@google.com
Diffstat (limited to 'tools/lib/bpf')
| -rw-r--r-- | tools/lib/bpf/libbpf.c | 16 |
1 files changed, 9 insertions, 7 deletions
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index cb106e8c42cb..ff3c0ee79d85 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -5277,11 +5277,11 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog) } insn[1].imm = ext->kcfg.data_off; } else /* EXT_KSYM */ { - if (ext->ksym.type_id) { /* typed ksyms */ + if (ext->ksym.type_id && ext->is_set) { /* typed ksyms */ insn[0].src_reg = BPF_PSEUDO_BTF_ID; insn[0].imm = ext->ksym.kernel_btf_id; insn[1].imm = ext->ksym.kernel_btf_obj_fd; - } else { /* typeless ksyms */ + } else { /* typeless ksyms or unresolved typed ksyms */ insn[0].imm = (__u32)ext->ksym.addr; insn[1].imm = ext->ksym.addr >> 32; } @@ -6608,11 +6608,8 @@ static int find_ksym_btf_id(struct bpf_object *obj, const char *ksym_name, break; } } - if (id <= 0) { - pr_warn("extern (%s ksym) '%s': failed to find BTF ID in kernel BTF(s).\n", - __btf_kind_str(kind), ksym_name); + if (id <= 0) return -ESRCH; - } *res_btf = btf; *res_btf_fd = btf_fd; @@ -6629,8 +6626,13 @@ static int bpf_object__resolve_ksym_var_btf_id(struct bpf_object *obj, struct btf *btf = NULL; id = find_ksym_btf_id(obj, ext->name, BTF_KIND_VAR, &btf, &btf_fd); - if (id < 0) + if (id == -ESRCH && ext->is_weak) { + return 0; + } else if (id < 0) { + pr_warn("extern (var ksym) '%s': not found in kernel BTF\n", + ext->name); return id; + } /* find local type_id */ local_type_id = ext->ksym.type_id; |