[PATCH RFC bpf-next 7/8] bpf: implement __aux kfunc argument suffix to fetch prog_aux

Benjamin Tissoires
2024-05-07T13:20:10Z

This allows kfunc to request the prog_aux environment in their
implementation, to have access to the originated bpf_prog for example.

Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

---

This is an RFC, and is not meant to be fully reviewed/applied as it is.
I'm posting this to show what I wanted to explain in
https://lore.kernel.org/bpf/mhkzkf4e23uvljtmwizwcxyuyat2tmfxn33xb4t7waafgmsa66@mcrzpj3b6ssx/
---
kernel/bpf/verifier.c | 40 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6fba9e2caa83..33b108db0025 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10909,6 +10909,11 @@ static bool is_kfunc_arg_sleepable_async_cb(const struct btf *btf, const struct
return btf_param_match_suffix(btf, arg, "__s_async");
}

+static bool is_kfunc_arg_prog_aux(const struct btf *btf, const struct btf_param *arg)
+{
+ return btf_param_match_suffix(btf, arg, "__aux");
+}
+
static bool is_kfunc_arg_scalar_with_name(const struct btf *btf,
const struct btf_param *arg,
const char *name)
@@ -11807,7 +11812,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_

t = btf_type_skip_modifiers(btf, args[i].type, NULL);

- if (is_kfunc_arg_ignore(btf, &args[i]))
+ if (is_kfunc_arg_ignore(btf, &args[i]) ||
+ is_kfunc_arg_prog_aux(btf, &args[i]))
continue;

if (btf_type_is_scalar(t)) {
@@ -19950,6 +19956,38 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
insn_buf[1] = ld_addrs[1];
insn_buf[2] = *insn;
*cnt = 3;
+ } else {
+ struct bpf_kfunc_call_arg_meta meta;
+ struct bpf_insn kfunc_insn = *insn;
+ const struct btf_param *args;
+ u32 i, nargs, prog_aux_arg;
+ const char *func_name;
+ int ret;
+
+ /* imm might not have func_id, so create a fake insn with the expected args */
+ kfunc_insn.imm = desc->func_id;
+
+ ret = fetch_kfunc_meta(env, &kfunc_insn, &meta, &func_name);
+ if (ret == 0) {
+ args = (const struct btf_param *)(meta.func_proto + 1);
+ nargs = btf_type_vlen(meta.func_proto);
+ prog_aux_arg = nargs;
+
+ for (i = 0; i < nargs; i++) {
+ if (is_kfunc_arg_prog_aux(meta.btf, &args[i]))
+ prog_aux_arg = i;
+ }
+
+ if (prog_aux_arg < nargs) {
+ struct bpf_insn ld_addrs[2] = { BPF_LD_IMM64(BPF_REG_1 + prog_aux_arg,
+ (long)env->prog->aux) };
+
+ insn_buf[0] = ld_addrs[0];
+ insn_buf[1] = ld_addrs[1];
+ insn_buf[2] = *insn;
+ *cnt = 3;
+ }
+ }
}
return 0;
}

--
2.44.0