From: Alexei Starovoitov <ast@xxxxxxxxxx>
Allow ld_imm64 insn with BPF_PSEUDO_BTF_ID to hold the address of kfunc.
PTR_MEM is already recognized for NULL-ness by is_branch_taken(),
so unresolved kfuncs will be seen as zero.
This allows BPF programs to detect at load time whether kfunc is present
in the kernel with bpf_kfunc_exists() macro.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
kernel/bpf/verifier.c | 7 +++++--
tools/lib/bpf/bpf_helpers.h | 3 +++
2 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 60793f793ca6..4e49d34d8cd6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -15955,8 +15955,8 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
goto err_put;
}
- if (!btf_type_is_var(t)) {
- verbose(env, "pseudo btf_id %d in ldimm64 isn't KIND_VAR.\n", id);
+ if (!btf_type_is_var(t) && !btf_type_is_func(t)) {
+ verbose(env, "pseudo btf_id %d in ldimm64 isn't KIND_VAR or KIND_FUNC\n", id);
err = -EINVAL;
goto err_put;
}
@@ -15990,6 +15990,9 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
aux->btf_var.reg_type = PTR_TO_BTF_ID | MEM_PERCPU;
aux->btf_var.btf = btf;
aux->btf_var.btf_id = type;
+ } else if (!btf_type_is_func(t)) {
+ aux->btf_var.reg_type = PTR_TO_MEM | MEM_RDONLY;
+ aux->btf_var.mem_size = 0;
} else if (!btf_type_is_struct(t)) {
const struct btf_type *ret;
const char *tname;
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index 7d12d3e620cc..43abe4c29409 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -177,6 +177,9 @@ enum libbpf_tristate {
#define __kptr_untrusted __attribute__((btf_type_tag("kptr_untrusted")))
#define __kptr __attribute__((btf_type_tag("kptr")))
+/* pass function pointer through asm otherwise compiler assumes that any function != 0 */
+#define bpf_kfunc_exists(fn) ({ void *__p = fn; asm ("" : "+r"(__p)); __p; })
+
#ifndef ___bpf_concat
#define ___bpf_concat(a, b) a ## b
#endif
--
2.34.1
