linux-kernel - [RFC tracing 2/4] tracing: support > 8 byte array filter predicates

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Date:   Sun,  7 Aug 2022 23:21:21 +0100
From:   Alan Maguire <alan.maguire@...cle.com>
To:     rostedt@...dmis.org
Cc:     corbet@....net, mingo@...hat.com, shuah@...nel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Alan Maguire <alan.maguire@...cle.com>
Subject: [RFC tracing 2/4] tracing: support > 8 byte array filter predicates

For > 8 byte values, allow simple binary '==', '!=' predicates
where the user passes in a hex ASCII representation of the
desired value.  This representation must match the field size
exactly, and a simple memory comparison between predicate and
actual values is carried out.  This will allow predicates with
for example IPv6 addresses to be supported, such as filtering
on ::1

	cd /sys/kernel/debug/tracing/events/tcp/tcp_receive_reset
	echo "saddr_v6 == 0x00000000000000000000000000000001" > filter

Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
---
 kernel/trace/trace_events_filter.c | 54 +++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 65e01c8d48d9..31c900b6a83c 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -147,6 +147,8 @@ enum {
 	PROCESS_OR	= 4,
 };
 
+static int filter_pred_memcmp(struct filter_pred *pred, void *event);
+
 /*
  * Without going into a formal proof, this explains the method that is used in
  * parsing the logical expressions.
@@ -583,8 +585,11 @@ predicate_parse(const char *str, int nr_parens, int nr_preds,
 	kfree(op_stack);
 	kfree(inverts);
 	if (prog_stack) {
-		for (i = 0; prog_stack[i].pred; i++)
+		for (i = 0; prog_stack[i].pred; i++) {
+			if (prog_stack[i].pred->fn == filter_pred_memcmp)
+				kfree((u8 *)prog_stack[i].pred->val);
 			kfree(prog_stack[i].pred);
+		}
 		kfree(prog_stack);
 	}
 	return ERR_PTR(ret);
@@ -841,6 +846,14 @@ static int filter_pred_none(struct filter_pred *pred, void *event)
 	return 0;
 }
 
+static int filter_pred_memcmp(struct filter_pred *pred, void *event)
+{
+	u8 *mem = (u8 *)(event + pred->offset);
+	u8 *cmp = (u8 *)(pred->val);
+
+	return (memcmp(mem, cmp, pred->field->size) == 0) ^ pred->not;
+}
+
 /*
  * regex_match_foo - Basic regex callbacks
  *
@@ -1443,6 +1456,45 @@ static int parse_pred(const char *str, void *data,
 		/* go past the last quote */
 		i++;
 
+	} else if (str[i] == '0' && tolower(str[i + 1]) == 'x' &&
+		   field->size > 8) {
+		u8 *pred_val;
+
+		/* For sizes > 8 bytes, we store a binary representation
+		 * for comparison; only '==' and '!=' are supported.
+		 * To keep things simple, the predicate value must specify
+		 * a value that matches the field size exactly, with leading
+		 * 0s if necessary.
+		 */
+		if (pred->op != OP_EQ && pred->op != OP_NE) {
+			parse_error(pe, FILT_ERR_ILLEGAL_FIELD_OP, pos + i);
+			goto err_free;
+		}
+
+		/* skip required 0x */
+		s += 2;
+		i += 2;
+
+		while (isalnum(str[i]))
+			i++;
+
+		len = i - s;
+		if (len != (field->size * 2)) {
+			parse_error(pe, FILT_ERR_ILLEGAL_FIELD_OP, pos + s);
+			goto err_free;
+		}
+
+		pred_val = kzalloc(field->size, GFP_KERNEL);
+		if (hex2bin(pred_val, str + s, field->size)) {
+			parse_error(pe, FILT_ERR_ILLEGAL_INTVAL, pos + s);
+			kfree(pred_val);
+			goto err_free;
+		}
+		pred->val = (u64)pred_val;
+		pred->fn = filter_pred_memcmp;
+		if (pred->op == OP_NE)
+			pred->not = 1;
+
 	} else if (isdigit(str[i]) || str[i] == '-') {
 
 		/* Make sure the field is not a string */
-- 
2.31.1