On Wed, Jul 07, 2021 at 11:47:47PM +0200, Jiri Olsa wrote:
>
> +static bool allow_get_func_ip_tracing(struct bpf_verifier_env *env)
> +{
> + return env->prog->jit_requested && IS_ENABLED(CONFIG_X86_64);
Why does it have to be gated by 'jited && x86_64' ?
It's gated by bpf trampoline and it's only implemented on x86_64 so far.
The trampoline has plenty of features. I would expect bpf trampoline
for arm64 to implement all of them. If not the func_ip would be just
one of the trampoline features that couldn't be implemented and at that
time we'd need a flag mask of a sort, but I'd rather push of feature
equivalence between trampoline implementations.
Then jited part also doesn't seem to be necessary.
The trampoline passed pointer to a stack in R1.
Interpreter should deal with BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8) insn
the same way and it should work, since trampoline prepared it.
What did I miss?
> +static int has_get_func_ip(struct bpf_verifier_env *env)
> +{
> + enum bpf_attach_type eatype = env->prog->expected_attach_type;
> + enum bpf_prog_type type = resolve_prog_type(env->prog);
> + int func_id = BPF_FUNC_get_func_ip;
> +
> + if (type == BPF_PROG_TYPE_TRACING) {
> + if (eatype != BPF_TRACE_FENTRY && eatype != BPF_TRACE_FEXIT &&
> + eatype != BPF_MODIFY_RETURN) {
> + verbose(env, "func %s#%d supported only for fentry/fexit/fmod_ret programs\n",
> + func_id_name(func_id), func_id);
> + return -ENOTSUPP;
> + }
> + if (!allow_get_func_ip_tracing(env)) {
> + verbose(env, "func %s#%d for tracing programs supported only for JITed x86_64\n",
> + func_id_name(func_id), func_id);
> + return -ENOTSUPP;
> + }
> + return 0;
> + }
> +
> + verbose(env, "func %s#%d not supported for program type %d\n",
> + func_id_name(func_id), func_id, type);
> + return -ENOTSUPP;
> +}
> +
> static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> int *insn_idx_p)
> {
> @@ -6225,6 +6256,12 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
> if (func_id == BPF_FUNC_get_stackid || func_id == BPF_FUNC_get_stack)
> env->prog->call_get_stack = true;
>
> + if (func_id == BPF_FUNC_get_func_ip) {
> + if (has_get_func_ip(env))
> + return -ENOTSUPP;
> + env->prog->call_get_func_ip = true;
> + }
> +
> if (changes_data)
> clear_all_pkt_pointers(env);
> return 0;
> @@ -12369,6 +12406,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> {
> struct bpf_prog *prog = env->prog;
> bool expect_blinding = bpf_jit_blinding_enabled(prog);
> + enum bpf_prog_type prog_type = resolve_prog_type(prog);
> struct bpf_insn *insn = prog->insnsi;
> const struct bpf_func_proto *fn;
> const int insn_cnt = prog->len;
> @@ -12702,6 +12740,21 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> continue;
> }
>
> + /* Implement bpf_get_func_ip inline. */
> + if (prog_type == BPF_PROG_TYPE_TRACING &&
> + insn->imm == BPF_FUNC_get_func_ip) {
> + /* Load IP address from ctx - 8 */
> + insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
> +
> + new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 1);
> + if (!new_prog)
> + return -ENOMEM;
> +
> + env->prog = prog = new_prog;
> + insn = new_prog->insnsi + i + delta;
> + continue;
> + }
> +
> patch_call_imm:
> fn = env->ops->get_func_proto(insn->imm, env->prog);
> /* all functions that have prototype and verifier allowed
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 64bd2d84367f..9edd3b1a00ad 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -948,6 +948,19 @@ const struct bpf_func_proto bpf_snprintf_btf_proto = {
> .arg5_type = ARG_ANYTHING,
> };
>
> +BPF_CALL_1(bpf_get_func_ip_tracing, void *, ctx)
> +{
> + /* Stub, the helper call is inlined in the program. */
> + return 0;
> +}
may be add a WARN in here that it should never be executed ?
Or may be add an actual implementation:
return ((u64 *)ctx)[-1];
and check that it works without inlining by the verifier?
