From: Kumar Kartikeya Dwivedi memxor@gmail.com
mainline inclusion from mainline-5.16-rc1 commit 466b2e13971ef65cd7b621ca3044be14028b002b category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Preserve these calls as it allows verifier to succeed in loading the program if they are determined to be unreachable after dead code elimination during program load. If not, the verifier will fail at runtime. This is done for ext->is_weak symbols similar to the case for variable ksyms.
Signed-off-by: Kumar Kartikeya Dwivedi memxor@gmail.com Signed-off-by: Alexei Starovoitov ast@kernel.org Acked-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/bpf/20211002011757.311265-8-memxor@gmail.com (cherry picked from commit 466b2e13971ef65cd7b621ca3044be14028b002b) Signed-off-by: Wang Yufen wangyufen@huawei.com --- tools/lib/bpf/libbpf.c | 24 +++++++++++++----------- 1 file changed, 13 insertions(+), 11 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index aa0c5b33bd75..1d6dead6ef34 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -3420,11 +3420,6 @@ static int bpf_object__collect_externs(struct bpf_object *obj) return -ENOTSUP; } } else if (strcmp(sec_name, KSYMS_SEC) == 0) { - if (btf_is_func(t) && ext->is_weak) { - pr_warn("extern weak function %s is unsupported\n", - ext->name); - return -ENOTSUP; - } ksym_sec = sec; ext->type = EXT_KSYM; skip_mods_and_typedefs(obj->btf, t->type, @@ -5363,8 +5358,13 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog) case RELO_EXTERN_FUNC: ext = &obj->externs[relo->sym_off]; insn[0].src_reg = BPF_PSEUDO_KFUNC_CALL; - insn[0].imm = ext->ksym.kernel_btf_id; - insn[0].off = ext->ksym.btf_fd_idx; + if (ext->is_set) { + insn[0].imm = ext->ksym.kernel_btf_id; + insn[0].off = ext->ksym.btf_fd_idx; + } else { /* unresolved weak kfunc */ + insn[0].imm = 0; + insn[0].off = 0; + } break; case RELO_SUBPROG_ADDR: if (insn[0].src_reg != BPF_PSEUDO_FUNC) { @@ -6751,9 +6751,9 @@ static int bpf_object__resolve_ksym_var_btf_id(struct bpf_object *obj, int id, err;
id = find_ksym_btf_id(obj, ext->name, BTF_KIND_VAR, &btf, &mod_btf); - if (id == -ESRCH && ext->is_weak) { - return 0; - } else if (id < 0) { + if (id < 0) { + if (id == -ESRCH && ext->is_weak) + return 0; pr_warn("extern (var ksym) '%s': not found in kernel BTF\n", ext->name); return id; @@ -6806,7 +6806,9 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
kfunc_id = find_ksym_btf_id(obj, ext->name, BTF_KIND_FUNC, &kern_btf, &mod_btf); if (kfunc_id < 0) { - pr_warn("extern (func ksym) '%s': not found in kernel BTF\n", + if (kfunc_id == -ESRCH && ext->is_weak) + return 0; + pr_warn("extern (func ksym) '%s': not found in kernel or module BTFs\n", ext->name); return kfunc_id; }