[PATCH bpf-next] libbpf: Fix sign extension of unaligned enums in btf_dump_get_enum_value()

[Hungyu Lin <dennylin0707@gmail.com>]

btf_dump_get_enum_value() reads unaligned enum values through
btf_dump_get_bitfield_value() with a zero bit size. That path
zero-extends the value instead of using the signed loads that are used
for aligned data, so a negative value of a signed enum loses its
enumerator name when the data is unaligned.

Fix this by copying unaligned enum data into an aligned buffer, after
checking that the whole value is within the data, and reading it with
the same loads as aligned data.

Fixes: 920d16af9b42 ("libbpf: BTF dumper support for typed data")
Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
---
 tools/lib/bpf/btf_dump.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index bbe86928b3ec..30fe3bb48df6 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -2329,16 +2329,13 @@ static int btf_dump_get_enum_value(struct btf_dump *d,
 				   __s64 *value)
 {
 	bool is_signed = btf_kflag(t);
+	char buf[8] __attribute__((aligned(8)));
 
-	if (!ptr_is_aligned(d->btf, id, data)) {
-		__u64 val;
-		int err;
-
-		err = btf_dump_get_bitfield_value(d, t, data, 0, 0, &val);
-		if (err)
-			return err;
-		*value = (__s64)val;
-		return 0;
+	if (t->size <= sizeof(buf) && !ptr_is_aligned(d->btf, id, data)) {
+		if (data + t->size > d->typed_dump->data_end)
+			return -E2BIG;
+		memcpy(buf, data, t->size);
+		data = buf;
 	}
 
 	switch (t->size) {

base-commit: 0021f17128de5dc0b19f1a523f448df2440d8088
-- 
2.43.0