From: KP Singh <kpsingh@kernel.org>
To: linux-security-module@vger.kernel.org, bpf@vger.kernel.org
Cc: ast@kernel.org, daniel@iogearbox.net, memxor@gmail.com,
James.Bottomley@HansenPartnership.com, paul@paul-moore.com,
KP Singh <kpsingh@kernel.org>
Subject: [PATCH bpf-next 06/13] bpf: resolve loader-style kfunc CALLs against prog BTF
Date: Fri, 22 May 2026 04:32:26 +0200 [thread overview]
Message-ID: <20260522023234.3778588-7-kpsingh@kernel.org> (raw)
In-Reply-To: <20260522023234.3778588-1-kpsingh@kernel.org>
gen_loader-emitted signed loaders cannot bake vmlinux BTF ids into
kfunc CALL imm at sign time. Add a new pseudo
BPF_PSEUDO_KFUNC_CALL_PROG_BTF that gen_loader emits in src_reg, with
imm holding the FUNC type id in the loader's own prog BTF.
In add_subprog_and_kfunc, look the FUNC up by name in vmlinux BTF,
patch imm with the resolved id, and rewrite src_reg back to
BPF_PSEUDO_KFUNC_CALL so downstream passes see a normal kfunc CALL.
Leave standard src_reg calls unchanged.
Signed-off-by: KP Singh <kpsingh@kernel.org>
---
include/linux/bpf_verifier.h | 6 ++++
include/uapi/linux/bpf.h | 5 ++++
kernel/bpf/verifier.c | 54 ++++++++++++++++++++++++++++++++--
tools/include/uapi/linux/bpf.h | 5 ++++
4 files changed, 67 insertions(+), 3 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 185b2aa43a42..396b85830996 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -959,6 +959,12 @@ static inline bool bpf_pseudo_kfunc_call(const struct bpf_insn *insn)
insn->src_reg == BPF_PSEUDO_KFUNC_CALL;
}
+static inline bool bpf_pseudo_kfunc_call_prog_btf(const struct bpf_insn *insn)
+{
+ return insn->code == (BPF_JMP | BPF_CALL) &&
+ insn->src_reg == BPF_PSEUDO_KFUNC_CALL_PROG_BTF;
+}
+
__printf(2, 0) void bpf_verifier_vlog(struct bpf_verifier_log *log,
const char *fmt, va_list args);
__printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 552bc5d9afbd..06056e714e8e 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1382,6 +1382,11 @@ enum {
* bpf_call->imm == btf_id of a BTF_KIND_FUNC in the running kernel
*/
#define BPF_PSEUDO_KFUNC_CALL 2
+/* when bpf_call->src_reg == BPF_PSEUDO_KFUNC_CALL_PROG_BTF,
+ * bpf_call->imm == btf_id of a BTF_KIND_FUNC in the program's
+ * prog BTF. The verifier resolves it to a vmlinux btf_id by name.
+ */
+#define BPF_PSEUDO_KFUNC_CALL_PROG_BTF 3
enum bpf_addr_space_cast {
BPF_ADDR_SPACE_CAST = 1,
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f0e45cfa5b34..1b5d06b9d74a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3088,6 +3088,47 @@ bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog)
return !!prog->aux->kfunc_tab;
}
+/*
+ * Resolve a gen_loader-emitted kfunc CALL by FUNC name in vmlinux BTF,
+ * then rewrite src_reg back to BPF_PSEUDO_KFUNC_CALL. Caller must have
+ * already filtered for BPF_PSEUDO_KFUNC_CALL_PROG_BTF.
+ */
+static int resolve_loader_kfunc(struct bpf_verifier_env *env,
+ struct bpf_insn *insn, int insn_idx)
+{
+ struct btf *prog_btf = env->prog->aux->btf;
+ const struct btf_type *t;
+ const char *name;
+ s32 vmlinux_id;
+
+ if (!prog_btf || !btf_vmlinux || insn->off) {
+ verbose(env, "kfunc call insn %d: PROG_BTF resolution requires prog BTF and insn->off == 0\n",
+ insn_idx);
+ return -EINVAL;
+ }
+ t = btf_type_by_id(prog_btf, insn->imm);
+ if (!t || !btf_type_is_func(t)) {
+ verbose(env, "kfunc call insn %d: imm %d is not a FUNC in prog BTF\n",
+ insn_idx, insn->imm);
+ return -EINVAL;
+ }
+ name = btf_name_by_offset(prog_btf, t->name_off);
+ if (!name || !name[0]) {
+ verbose(env, "kfunc call insn %d: prog-BTF FUNC has no name\n",
+ insn_idx);
+ return -EINVAL;
+ }
+ vmlinux_id = btf_find_by_name_kind(btf_vmlinux, name, BTF_KIND_FUNC);
+ if (vmlinux_id < 0) {
+ verbose(env, "kfunc call insn %d: %s not found in vmlinux BTF\n",
+ insn_idx, name);
+ return vmlinux_id;
+ }
+ insn->imm = vmlinux_id;
+ insn->src_reg = BPF_PSEUDO_KFUNC_CALL;
+ return 0;
+}
+
static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
{
struct bpf_subprog_info *subprog = env->subprog_info;
@@ -3101,7 +3142,8 @@ static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
for (i = 0; i < insn_cnt; i++, insn++) {
if (!bpf_pseudo_func(insn) && !bpf_pseudo_call(insn) &&
- !bpf_pseudo_kfunc_call(insn))
+ !bpf_pseudo_kfunc_call(insn) &&
+ !bpf_pseudo_kfunc_call_prog_btf(insn))
continue;
if (!env->bpf_capable) {
@@ -3109,10 +3151,16 @@ static int add_subprog_and_kfunc(struct bpf_verifier_env *env)
return -EPERM;
}
- if (bpf_pseudo_func(insn) || bpf_pseudo_call(insn))
+ if (bpf_pseudo_func(insn) || bpf_pseudo_call(insn)) {
ret = add_subprog(env, i + insn->imm + 1);
- else
+ } else {
+ if (bpf_pseudo_kfunc_call_prog_btf(insn)) {
+ ret = resolve_loader_kfunc(env, insn, i);
+ if (ret < 0)
+ return ret;
+ }
ret = bpf_add_kfunc_call(env, insn->imm, insn->off);
+ }
if (ret < 0)
return ret;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 677be9a47347..d4f7f3e0aaa3 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1382,6 +1382,11 @@ enum {
* bpf_call->imm == btf_id of a BTF_KIND_FUNC in the running kernel
*/
#define BPF_PSEUDO_KFUNC_CALL 2
+/* when bpf_call->src_reg == BPF_PSEUDO_KFUNC_CALL_PROG_BTF,
+ * bpf_call->imm == btf_id of a BTF_KIND_FUNC in the program's
+ * prog BTF. The verifier resolves it to a vmlinux btf_id by name.
+ */
+#define BPF_PSEUDO_KFUNC_CALL_PROG_BTF 3
enum bpf_addr_space_cast {
BPF_ADDR_SPACE_CAST = 1,
--
2.53.0
next prev parent reply other threads:[~2026-05-22 2:32 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-22 2:32 [PATCH bpf-next 00/13] Signed BPF + IPE Policies KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 01/13] bpf: expose signature verdict to LSMs via bpf_prog_aux KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 02/13] bpf: include prog BTF in the signed loader signature scope KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 03/13] bpf, libbpf: load prog BTF in the skel_internal loader KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 04/13] bpf: add bpf_loader_verify_metadata kfunc KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 05/13] bpf: compute prog->digest at BPF_PROG_LOAD entry KP Singh
2026-05-22 2:32 ` KP Singh [this message]
2026-05-22 2:32 ` [PATCH bpf-next 07/13] libbpf: generate prog BTF for loader programs KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 08/13] bpftool gen: embed loader prog BTF in the lskel header KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 09/13] lsm: add bpf_prog_load_post_integrity hook KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 10/13] bpf: invoke security_bpf_prog_load_post_integrity from the metadata kfunc KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 11/13] ipe: add BPF program signature properties KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 12/13] ipe: gate post-integrity BPF program loads KP Singh
2026-05-22 2:32 ` [PATCH bpf-next 13/13] selftests/bpf: add IPE BPF policy integration tests KP Singh
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