When updating per-CPU maps via the lightweight skeleton loader, use a single value slot across all CPUs. This avoids two potential issues when updating on an M-CPU kernel with N cached slots (N < M), especially when N is much smaller than M: 1) The update may trigger a page fault when copying data from the last slot, as the read may go beyond the allocated buffer. 2) The update may copy unexpected data from slots [N, M-1]. Signed-off-by: Leon Hwang --- kernel/bpf/syscall.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index b73b25c63073..f0f3785ef57d 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -1785,6 +1785,21 @@ static int map_update_elem(union bpf_attr *attr, bpfptr_t uattr) goto err_put; } + /* + * When updating per-CPU maps via the lightweight skeleton + * loader, use a single value slot across all CPUs. This avoids + * two potential issues when updating on an M-CPU kernel with + * N cached slots (N < M), especially when N is much smaller + * than M: + * 1) The update may trigger a page fault when copying data from + * the last slot, as the read may go beyond the allocated + * buffer. + * 2) The update may copy unexpected data from slots [N, M-1]. + */ + if (bpfptr_is_kernel(uattr) && bpf_map_supports_cpu_flags(map->map_type) && + !(attr->flags & (BPF_F_CPU | BPF_F_ALL_CPUS))) + attr->flags |= BPF_F_ALL_CPUS; + err = bpf_map_check_op_flags(map, attr->flags, ~0); if (err) goto err_put; -- 2.53.0