[PATCH 5.15 018/164] libbpf: Fix dumping big-endian bitfields

Sasha Levin
2026-02-28T18:15:20Z

From: Ilya Leoshkevich <iii@linux.ibm.com>

[ Upstream commit c9e982b879465ca74e3593ce82808aa259265a71 ]

On big-endian arches not only bytes, but also bits are numbered in
reverse order (see e.g. S/390 ELF ABI Supplement, but this is also true
for other big-endian arches as well).

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211013160902.428340-3-iii@linux.ibm.com
Stable-dep-of: 5714ca8cba5e ("libbpf: Fix OOB read in btf_dump_get_bitfield_value")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/btf_dump.c | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index d62b2d2e8aacb..91ab07901a1bc 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -1656,29 +1656,28 @@ static int btf_dump_get_bitfield_value(struct btf_dump *d,
__u64 *value)
{
__u16 left_shift_bits, right_shift_bits;
- __u8 nr_copy_bits, nr_copy_bytes;
const __u8 *bytes = data;
- int sz = t->size;
+ __u8 nr_copy_bits;
__u64 num = 0;
int i;

/* Maximum supported bitfield size is 64 bits */
- if (sz > 8) {
- pr_warn("unexpected bitfield size %d\n", sz);
+ if (t->size > 8) {
+ pr_warn("unexpected bitfield size %d\n", t->size);
return -EINVAL;
}

/* Bitfield value retrieval is done in two steps; first relevant bytes are
* stored in num, then we left/right shift num to eliminate irrelevant bits.
*/
- nr_copy_bits = bit_sz + bits_offset;
- nr_copy_bytes = t->size;
#if __BYTE_ORDER == __LITTLE_ENDIAN
- for (i = nr_copy_bytes - 1; i >= 0; i--)
+ for (i = t->size - 1; i >= 0; i--)
num = num * 256 + bytes[i];
+ nr_copy_bits = bit_sz + bits_offset;
#elif __BYTE_ORDER == __BIG_ENDIAN
- for (i = 0; i < nr_copy_bytes; i++)
+ for (i = 0; i < t->size; i++)
num = num * 256 + bytes[i];
+ nr_copy_bits = t->size * 8 - bits_offset;
#else
# error "Unrecognized __BYTE_ORDER__"
#endif
--
2.51.0