Re: [PATCHv3 bpf-next 3/7] bpf: Add bpf_get_func_ip helper for tracing programs
From: Alexei Starovoitov <hidden>
Date: 2021-07-08 02:11:29
Also in:
bpf
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?
quoted hunk ↗ jump to hunk
+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 alloweddiff --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?