From 7cf9cd98cf6f0df3befc167ca6b54c07014d71de Mon Sep 17 00:00:00 2001 From: Leon Hwang Date: Wed, 24 Jun 2026 23:51:14 +0800 Subject: [PATCH] bpf: Copy per-CPU map value padding in copy_map_value_long() In kernel, per-CPU map elements are stored with round_up(map->value_size, 8) bytes. On UAPI lookup paths, it copies the rounded size for each CPU into a temporary buffer. However, copy_map_value_long() passes 'map->value_size' to bpf_obj_memcpy(). When the map has special fields, bpf_obj_memcpy() copies around those fields with memcpy(), and does not copy the tail padding between 'map->value_size' and round_up(map->value_size, 8). The temporary UAPI lookup buffers are allocated without __GFP_ZERO. As a result, when the per-CPU map's value size is not equal to round_up(map->value_size, 8), UAPI LOOKUP_ELEM and its variants can return stale heap contents from that padding to user space. The same issue applies to bpf_iter for per-CPU maps. Pass round_up(map->value_size, 8) to bpf_obj_memcpy() from copy_map_value_long(), so per-CPU maps both with and without special fields copy the entire per-CPU slot. Remove the now redundant round_up() from bpf_obj_memcpy()'s long_memcpy path. Fixes: 448325199f57 ("bpf: Add copy_map_value_long to copy to remote percpu memory") Signed-off-by: Leon Hwang Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20260624155115.85196-2-leon.hwang@linux.dev --- include/linux/bpf.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 7719f6528445..ba09795e0bfd 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -570,7 +570,7 @@ static inline void bpf_obj_memcpy(struct btf_record *rec, if (IS_ERR_OR_NULL(rec)) { if (long_memcpy) - bpf_long_memcpy(dst, src, round_up(size, 8)); + bpf_long_memcpy(dst, src, size); else memcpy(dst, src, size); return; @@ -593,7 +593,7 @@ static inline void copy_map_value(struct bpf_map *map, void *dst, void *src) static inline void copy_map_value_long(struct bpf_map *map, void *dst, void *src) { - bpf_obj_memcpy(map->record, dst, src, map->value_size, true); + bpf_obj_memcpy(map->record, dst, src, round_up(map->value_size, 8), true); } static inline void bpf_obj_swap_uptrs(const struct btf_record *rec, void *dst, void *src)