bpf: add support for bpf_call to interpreter

though bpf_call is still the same call instruction and
calling convention 'bpf to bpf' and 'bpf to helper' is the same
the interpreter has to oparate on 'struct bpf_insn *'.
To distinguish these two cases add a kernel internal opcode and
mark call insns with it.
This opcode is seen by interpreter only. JITs will never see it.
Also add tiny bit of debug code to aid interpreter debugging.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 36 insertions, 0 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index df1ded3faf1d..cdc1f043c69b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1458,6 +1458,21 @@ static int update_stack_depth(struct bpf_verifier_env *env,
 	return 0;
 }
 
+static int get_callee_stack_depth(struct bpf_verifier_env *env,
+				  const struct bpf_insn *insn, int idx)
+{
+	int start = idx + insn->imm + 1, subprog;
+
+	subprog = find_subprog(env, start);
+	if (subprog < 0) {
+		WARN_ONCE(1, "verifier bug. No program starts at insn %d\n",
+			  start);
+		return -EFAULT;
+	}
+	subprog++;
+	return env->subprog_stack_depth[subprog];
+}
+
 /* check whether memory at (regno + off) is accessible for t = (read | write)
  * if t==write, value_regno is a register which value is stored into memory
  * if t==read, value_regno is a register which will receive the value from memory
@@ -4997,6 +5012,24 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 	return 0;
 }
 
+static int fixup_call_args(struct bpf_verifier_env *env)
+{
+	struct bpf_prog *prog = env->prog;
+	struct bpf_insn *insn = prog->insnsi;
+	int i, depth;
+
+	for (i = 0; i < prog->len; i++, insn++) {
+		if (insn->code != (BPF_JMP | BPF_CALL) ||
+		    insn->src_reg != BPF_PSEUDO_CALL)
+			continue;
+		depth = get_callee_stack_depth(env, insn, i);
+		if (depth < 0)
+			return depth;
+		bpf_patch_call_args(insn, depth);
+	}
+	return 0;
+}
+
 /* fixup insn->imm field of bpf_call instructions
  * and inline eligible helpers as explicit sequence of BPF instructions
  *
@@ -5225,6 +5258,9 @@ skip_full_check:
 	if (ret == 0)
 		ret = fixup_bpf_calls(env);
 
+	if (ret == 0)
+		ret = fixup_call_args(env);
+
 	if (log->level && bpf_verifier_log_full(log))
 		ret = -ENOSPC;
 	if (log->level && !log->ubuf) {