From cb4a21ea592f5753ab54cd8688306cf6423783a8 Mon Sep 17 00:00:00 2001 From: David Vernet Date: Sat, 28 Jan 2023 08:15:37 -0600 Subject: [PATCH] bpf: Build-time assert that cpumask offset is zero The first element of a struct bpf_cpumask is a cpumask_t. This is done to allow struct bpf_cpumask to be cast to a struct cpumask. If this element were ever moved to another field, any BPF program passing a struct bpf_cpumask * to a kfunc expecting a const struct cpumask * would immediately fail to load. Add a build-time assertion so this is assumption is captured and verified. Signed-off-by: David Vernet Link: https://lore.kernel.org/r/20230128141537.100777-1-void@manifault.com Signed-off-by: Alexei Starovoitov --- kernel/bpf/cpumask.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c index 25355a0a367a..6bbb67dfc998 100644 --- a/kernel/bpf/cpumask.c +++ b/kernel/bpf/cpumask.c @@ -52,6 +52,9 @@ struct bpf_cpumask *bpf_cpumask_create(void) { struct bpf_cpumask *cpumask; + /* cpumask must be the first element so struct bpf_cpumask be cast to struct cpumask. */ + BUILD_BUG_ON(offsetof(struct bpf_cpumask, cpumask) != 0); + cpumask = bpf_mem_alloc(&bpf_cpumask_ma, sizeof(*cpumask)); if (!cpumask) return NULL;