From 20c09d92faeefb8536f705d3a4629e0dc314c8a1 Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Thu, 2 Mar 2023 20:14:43 -0800 Subject: bpf: Introduce kptr_rcu. The life time of certain kernel structures like 'struct cgroup' is protected by RCU. Hence it's safe to dereference them directly from __kptr tagged pointers in bpf maps. The resulting pointer is MEM_RCU and can be passed to kfuncs that expect KF_RCU. Derefrence of other kptr-s returns PTR_UNTRUSTED. For example: struct map_value { struct cgroup __kptr *cgrp; }; SEC("tp_btf/cgroup_mkdir") int BPF_PROG(test_cgrp_get_ancestors, struct cgroup *cgrp_arg, const char *path) { struct cgroup *cg, *cg2; cg = bpf_cgroup_acquire(cgrp_arg); // cg is PTR_TRUSTED and ref_obj_id > 0 bpf_kptr_xchg(&v->cgrp, cg); cg2 = v->cgrp; // This is new feature introduced by this patch. // cg2 is PTR_MAYBE_NULL | MEM_RCU. // When cg2 != NULL, it's a valid cgroup, but its percpu_ref could be zero if (cg2) bpf_cgroup_ancestor(cg2, level); // safe to do. } Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Acked-by: Tejun Heo Acked-by: David Vernet Link: https://lore.kernel.org/bpf/20230303041446.3630-4-alexei.starovoitov@gmail.com --- net/bpf/test_run.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'net/bpf') diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 6f3d654b3339..6a8b33a103a4 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -737,6 +737,7 @@ __bpf_kfunc void bpf_kfunc_call_test_mem_len_fail2(u64 *mem, int len) __bpf_kfunc void bpf_kfunc_call_test_ref(struct prog_test_ref_kfunc *p) { + /* p != NULL, but p->cnt could be 0 */ } __bpf_kfunc void bpf_kfunc_call_test_destructive(void) @@ -784,7 +785,7 @@ BTF_ID_FLAGS(func, bpf_kfunc_call_test_fail3) BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_pass1) BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_fail1) BTF_ID_FLAGS(func, bpf_kfunc_call_test_mem_len_fail2) -BTF_ID_FLAGS(func, bpf_kfunc_call_test_ref, KF_TRUSTED_ARGS) +BTF_ID_FLAGS(func, bpf_kfunc_call_test_ref, KF_TRUSTED_ARGS | KF_RCU) BTF_ID_FLAGS(func, bpf_kfunc_call_test_destructive, KF_DESTRUCTIVE) BTF_ID_FLAGS(func, bpf_kfunc_call_test_static_unused_arg) BTF_SET8_END(test_sk_check_kfunc_ids) -- cgit v1.2.3-70-g09d2