perf dwarf-aux: Check allowed DWARF Ops

The DWARF location expression can be fairly complex and it'd be hard
to match it with the condition correctly. So let's be conservative
and only allow simple expressions. For now it just checks the first
operation in the list. The following operations looks ok:

* DW_OP_stack_value
* DW_OP_deref_size
* DW_OP_deref
* DW_OP_piece

To refuse complex (and unsupported) location expressions, add
check_allowed_ops() to compare the rest of the list. It seems earlier
result contained those unsupported expressions. For example, I found
some local struct variable is placed like below.

<2><43d1517>: Abbrev Number: 62 (DW_TAG_variable)
<43d1518> DW_AT_location : 15 byte block: 91 50 93 8 91 78 93 4 93 84 8 91 68 93 4
(DW_OP_fbreg: -48; DW_OP_piece: 8;
DW_OP_fbreg: -8; DW_OP_piece: 4;
DW_OP_piece: 1028;
DW_OP_fbreg: -24; DW_OP_piece: 4)

Another example is something like this.

0057c8be ffffffffffffffff ffffffff812109f0 (base address)
0057c8ce ffffffff812112b5 ffffffff812112c8 (DW_OP_breg3 (rbx): 0;
DW_OP_constu: 18446744073709551612;
DW_OP_and;
DW_OP_stack_value)

It should refuse them. After the change, the stat shows:

Annotate data type stats:
total 294, ok 158 (53.7%), bad 136 (46.3%)
-----------------------------------------------------------
30 : no_sym
32 : no_mem_ops
53 : no_var
14 : no_typeinfo
7 : bad_offset

Acked-by: Masami Hiramatsu (Google) <[e-mail]>
Reviewed-by: Ian Rogers <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>

tools/perf/util/dwarf-aux.c

···
 	return true;
 }
 
+static bool check_allowed_ops(Dwarf_Op *ops, size_t nops)
+{
+	/* The first op is checked separately */
+	ops++;
+	nops--;
+
+	/*
+	 * It needs to make sure if the location expression matches to the given
+	 * register and offset exactly.  Thus it rejects any complex expressions
+	 * and only allows a few of selected operators that doesn't change the
+	 * location.
+	 */
+	while (nops) {
+		switch (ops->atom) {
+		case DW_OP_stack_value:
+		case DW_OP_deref_size:
+		case DW_OP_deref:
+		case DW_OP_piece:
+			break;
+		default:
+			return false;
+		}
+		ops++;
+		nops--;
+	}
+	return true;
+}
+
 /* Only checks direct child DIEs in the given scope. */
 static int __die_find_var_reg_cb(Dwarf_Die *die_mem, void *arg)
 {
···
 		/* Local variables accessed using frame base register */
 		if (data->is_fbreg && ops->atom == DW_OP_fbreg &&
 		    data->offset >= (int)ops->number &&
+		    check_allowed_ops(ops, nops) &&
 		    match_var_offset(die_mem, data, data->offset, ops->number))
 			return DIE_FIND_CB_END;
 
 		/* Only match with a simple case */
 		if (data->reg < DWARF_OP_DIRECT_REGS) {
-			if (ops->atom == (DW_OP_reg0 + data->reg) && nops == 1)
+			/* pointer variables saved in a register 0 to 31 */
+			if (ops->atom == (DW_OP_reg0 + data->reg) &&
+			    check_allowed_ops(ops, nops))
 				return DIE_FIND_CB_END;
 
 			/* Local variables accessed by a register + offset */
 			if (ops->atom == (DW_OP_breg0 + data->reg) &&
+			    check_allowed_ops(ops, nops) &&
 			    match_var_offset(die_mem, data, data->offset, ops->number))
 				return DIE_FIND_CB_END;
 		} else {
+			/* pointer variables saved in a register 32 or above */
 			if (ops->atom == DW_OP_regx && ops->number == data->reg &&
-			    nops == 1)
+			    check_allowed_ops(ops, nops))
 				return DIE_FIND_CB_END;
 
 			/* Local variables accessed by a register + offset */
 			if (ops->atom == DW_OP_bregx && data->reg == ops->number &&
+			    check_allowed_ops(ops, nops) &&
 			    match_var_offset(die_mem, data, data->offset, ops->number2))
 				return DIE_FIND_CB_END;
 		}
···
 		if (data->addr < ops->number)
 			continue;
 
-		if (match_var_offset(die_mem, data, data->addr, ops->number))
+		if (check_allowed_ops(ops, nops) &&
+		    match_var_offset(die_mem, data, data->addr, ops->number))
 			return DIE_FIND_CB_END;
 	}
 	return DIE_FIND_CB_SIBLING;
···
 		return -1;
 
 	if (!dwarf_cfi_addrframe(cfi, pc, &frame) &&
-	    !dwarf_frame_cfa(frame, &ops, &nops) && nops == 1) {
+	    !dwarf_frame_cfa(frame, &ops, &nops) &&
+	    check_allowed_ops(ops, nops)) {
 		*preg = reg_from_dwarf_op(ops);
 		*poffset = offset_from_dwarf_op(ops);
 		return 0;