bpf: Undo internal BPF_PROBE_MEM in BPF insns dump

BPF_PROBE_MEM is kernel-internal implmementation details. When dumping BPF
instructions to user-space, it needs to be replaced back with BPF_MEM mode.

Fixes: 2a02759e ("bpf: Add support for BTF pointers to interpreter")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200613002115.1632142-1-andriin@fb.com

kernel/bpf/syscall.c

@@ -3158,6 +3158,7 @@ static struct bpf_insn *bpf_insn_prepare_dump(const struct bpf_prog *prog)
 	struct bpf_insn *insns;
 	u32 off, type;
 	u64 imm;
+	u8 code;
 	int i;
 
 	insns = kmemdup(prog->insnsi, bpf_prog_insn_size(prog),
@@ -3166,21 +3167,27 @@ static struct bpf_insn *bpf_insn_prepare_dump(const struct bpf_prog *prog)
 		return insns;
 
 	for (i = 0; i < prog->len; i++) {
-		if (insns[i].code == (BPF_JMP | BPF_TAIL_CALL)) {
+		code = insns[i].code;
+
+		if (code == (BPF_JMP | BPF_TAIL_CALL)) {
 			insns[i].code = BPF_JMP | BPF_CALL;
 			insns[i].imm = BPF_FUNC_tail_call;
 			/* fall-through */
 		}
-		if (insns[i].code == (BPF_JMP | BPF_CALL) ||
-		    insns[i].code == (BPF_JMP | BPF_CALL_ARGS)) {
-			if (insns[i].code == (BPF_JMP | BPF_CALL_ARGS))
+		if (code == (BPF_JMP | BPF_CALL) ||
+		    code == (BPF_JMP | BPF_CALL_ARGS)) {
+			if (code == (BPF_JMP | BPF_CALL_ARGS))
 				insns[i].code = BPF_JMP | BPF_CALL;
 			if (!bpf_dump_raw_ok())
 				insns[i].imm = 0;
 			continue;
 		}
+		if (BPF_CLASS(code) == BPF_LDX && BPF_MODE(code) == BPF_PROBE_MEM) {
+			insns[i].code = BPF_LDX | BPF_SIZE(code) | BPF_MEM;
+			continue;
+		}
 
-		if (insns[i].code != (BPF_LD | BPF_IMM | BPF_DW))
+		if (code != (BPF_LD | BPF_IMM | BPF_DW))
 			continue;
 
 		imm = ((u64)insns[i + 1].imm << 32) | (u32)insns[i].imm;