[PATCH 2/8] bpf: Add bpf_get_func_ip kprobe helper for fprobe link

Jiri Olsa
2022-02-02T13:53:53Z

Adding support to call get_func_ip_fprobe helper from kprobe
programs attached by fprobe link.

Also adding support to inline it, because it's single load
instruction.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
kernel/bpf/verifier.c | 19 ++++++++++++++++++-
kernel/trace/bpf_trace.c | 16 +++++++++++++++-
2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1ae41d0cf96c..a745ded00635 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -13625,7 +13625,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
continue;
}

- /* Implement bpf_get_func_ip inline. */
+ /* Implement tracing bpf_get_func_ip inline. */
if (prog_type == BPF_PROG_TYPE_TRACING &&
insn->imm == BPF_FUNC_get_func_ip) {
/* Load IP address from ctx - 16 */
@@ -13640,6 +13640,23 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
continue;
}

+ /* Implement kprobe/fprobe bpf_get_func_ip inline. */
+ if (prog_type == BPF_PROG_TYPE_KPROBE &&
+ eatype == BPF_TRACE_FPROBE &&
+ insn->imm == BPF_FUNC_get_func_ip) {
+ /* Load IP address from ctx (struct pt_regs) ip */
+ insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
+ offsetof(struct pt_regs, ip));
+
+ 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 a2024ba32a20..28e59e31e3db 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1036,6 +1036,19 @@ static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
.arg1_type = ARG_PTR_TO_CTX,
};

+BPF_CALL_1(bpf_get_func_ip_fprobe, struct pt_regs *, regs)
+{
+ /* This helper call is inlined by verifier. */
+ return regs->ip;
+}
+
+static const struct bpf_func_proto bpf_get_func_ip_proto_fprobe = {
+ .func = bpf_get_func_ip_fprobe,
+ .gpl_only = false,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_CTX,
+};
+
BPF_CALL_1(bpf_get_attach_cookie_trace, void *, ctx)
{
struct bpf_trace_run_ctx *run_ctx;
@@ -1279,7 +1292,8 @@ kprobe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_override_return_proto;
#endif
case BPF_FUNC_get_func_ip:
- return &bpf_get_func_ip_proto_kprobe;
+ return prog->expected_attach_type == BPF_TRACE_FPROBE ?
+ &bpf_get_func_ip_proto_fprobe : &bpf_get_func_ip_proto_kprobe;
case BPF_FUNC_get_attach_cookie:
return &bpf_get_attach_cookie_proto_trace;
default:
--
2.34.1