[ Upstream commit 05a68ce5fa51a83c360381630f823545c5757aa2 ]
For kuprobe and tracepoint bpf programs, kernel calls trace_call_bpf() which calls BPF_PROG_RUN_ARRAY_CHECK() to run the program array. Currently, BPF_PROG_RUN_ARRAY_CHECK() also calls bpf_cgroup_storage_set() to set percpu cgroup local storage with NULL value. This is due to Commit 394e40a29788 ("bpf: extend bpf_prog_array to store pointers to the cgroup storage") which modified __BPF_PROG_RUN_ARRAY() to call bpf_cgroup_storage_set() and this macro is also used by BPF_PROG_RUN_ARRAY_CHECK().
kuprobe and tracepoint programs are not allowed to call bpf_get_local_storage() helper hence does not access percpu cgroup local storage. Let us change BPF_PROG_RUN_ARRAY_CHECK() not to modify percpu cgroup local storage.
The issue is observed when I tried to debug [1] where percpu data is overwritten due to preempt_disable -> migration_disable change. This patch does not completely fix the above issue, which will be addressed separately, e.g., multiple cgroup prog runs may preempt each other. But it does fix any potential issue caused by tracing program overwriting percpu cgroup storage: - in a busy system, a tracing program is to run between bpf_cgroup_storage_set() and the cgroup prog run. - a kprobe program is triggered by a helper in cgroup prog before bpf_get_local_storage() is called.
[1] https://lore.kernel.org/bpf/CAKH8qBuXCfUz=w8L+Fj74OaUpbosO29niYwTki7e3Ag044_...
Fixes: 394e40a29788 ("bpf: extend bpf_prog_array to store pointers to the cgroup storage") Signed-off-by: Yonghong Song yhs@fb.com Signed-off-by: Alexei Starovoitov ast@kernel.org Acked-by: Roman Gushchin guro@fb.com Link: https://lore.kernel.org/bpf/20210309185028.3763817-1-yhs@fb.com Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/bpf.h | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 6e585dbc10df..f4242865cc86 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1066,7 +1066,7 @@ int bpf_prog_array_copy(struct bpf_prog_array *old_array, struct bpf_prog *include_prog, struct bpf_prog_array **new_array);
-#define __BPF_PROG_RUN_ARRAY(array, ctx, func, check_non_null) \ +#define __BPF_PROG_RUN_ARRAY(array, ctx, func, check_non_null, set_cg_storage) \ ({ \ struct bpf_prog_array_item *_item; \ struct bpf_prog *_prog; \ @@ -1079,7 +1079,8 @@ int bpf_prog_array_copy(struct bpf_prog_array *old_array, goto _out; \ _item = &_array->items[0]; \ while ((_prog = READ_ONCE(_item->prog))) { \ - bpf_cgroup_storage_set(_item->cgroup_storage); \ + if (set_cg_storage) \ + bpf_cgroup_storage_set(_item->cgroup_storage); \ _ret &= func(_prog, ctx); \ _item++; \ } \ @@ -1140,10 +1141,10 @@ _out: \ })
#define BPF_PROG_RUN_ARRAY(array, ctx, func) \ - __BPF_PROG_RUN_ARRAY(array, ctx, func, false) + __BPF_PROG_RUN_ARRAY(array, ctx, func, false, true)
#define BPF_PROG_RUN_ARRAY_CHECK(array, ctx, func) \ - __BPF_PROG_RUN_ARRAY(array, ctx, func, true) + __BPF_PROG_RUN_ARRAY(array, ctx, func, true, false)
#ifdef CONFIG_BPF_SYSCALL DECLARE_PER_CPU(int, bpf_prog_active);