bpf: Let verifier consider {task,cgroup} is trusted in bpf_iter_reg

BTF_TYPE_SAFE_TRUSTED(struct bpf_iter__task) in verifier.c wanted to
teach BPF verifier that bpf_iter__task -> task is a trusted ptr. But it
doesn't work well.

The reason is, bpf_iter__task -> task would go through btf_ctx_access()
which enforces the reg_type of 'task' is ctx_arg_info->reg_type, and in
task_iter.c, we actually explicitly declare that the
ctx_arg_info->reg_type is PTR_TO_BTF_ID_OR_NULL.

Actually we have a previous case like this[1] where PTR_TRUSTED is added to
the arg flag for map_iter.

This patch sets ctx_arg_info->reg_type is PTR_TO_BTF_ID_OR_NULL |
PTR_TRUSTED in task_reg_info.

Similarly, bpf_cgroup_reg_info -> cgroup is also PTR_TRUSTED since we are
under the protection of cgroup_mutex and we would check cgroup_is_dead()
in __cgroup_iter_seq_show().

This patch is to improve the user experience of the newly introduced
bpf_iter_css_task kfunc before hitting the mainline. The Fixes tag is
pointing to the commit introduced the bpf_iter_css_task kfunc.

Link[1]:https://lore.kernel.org/all/20230706133932.45883-3-aspsk@isovalent.com/

Fixes: 9c66dc94b62a ("bpf: Introduce css_task open-coded iterator kfuncs")
Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20231107132204.912120-2-zhouchuyi@bytedance.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

diff --git a/kernel/bpf/cgroup_iter.c b/kernel/bpf/cgroup_iter.c
index d1b5c5618dd74cde29106dcc44733ad12a50ebc5..f04a468cf6a72688121ced9e4ddcf0555b7758c5 100644 (file)
--- a/kernel/bpf/cgroup_iter.c
+++ b/kernel/bpf/cgroup_iter.c
@@ -282,7 +282,7 @@ static struct bpf_iter_reg bpf_cgroup_reg_info = {
        .ctx_arg_info_size      = 1,
        .ctx_arg_info           = {
                { offsetof(struct bpf_iter__cgroup, cgroup),
-                 PTR_TO_BTF_ID_OR_NULL },
+                 PTR_TO_BTF_ID_OR_NULL | PTR_TRUSTED },
        },
        .seq_info               = &cgroup_iter_seq_info,
 };

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 4e156dca48de957b2e91e2566a29d649b62b0095..26082b97894d3c0d64f4c909122ec3820f73f197 100644 (file)
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -704,7 +704,7 @@ static struct bpf_iter_reg task_reg_info = {
        .ctx_arg_info_size      = 1,
        .ctx_arg_info           = {
                { offsetof(struct bpf_iter__task, task),
-                 PTR_TO_BTF_ID_OR_NULL },
+                 PTR_TO_BTF_ID_OR_NULL | PTR_TRUSTED },
        },
        .seq_info               = &task_seq_info,
        .fill_link_info         = bpf_iter_fill_link_info,