bybrooklyn/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-04-18 14:53:58 -04:00
Code Issues Packages Projects Releases Wiki Activity

bpf: Introduce kptr_rcu.

Browse Source 
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 <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20230303041446.3630-4-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov
2023-03-02 20:14:43 -08:00
committed by Daniel Borkmann
parent 8d093b4e95
commit 20c09d92fa
9 changed files with 65 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
tools/testing/selftests/bpf/progs/map_kptr_fail.c
View File

@@ -281,7 +281,7 @@ int reject_kptr_get_bad_type_match(struct __sk_buff *ctx)
}
SEC("?tc")
__failure __msg("R1 type=untrusted_ptr_or_null_ expected=percpu_ptr_")
__failure __msg("R1 type=rcu_ptr_or_null_ expected=percpu_ptr_")
int mark_ref_as_untrusted_or_null(struct __sk_buff *ctx)
{
struct map_value *v;
@@ -316,7 +316,7 @@ int reject_untrusted_store_to_ref(struct __sk_buff *ctx)
}
SEC("?tc")
__failure __msg("R2 type=untrusted_ptr_ expected=ptr_")
__failure __msg("R2 must be referenced")
int reject_untrusted_xchg(struct __sk_buff *ctx)
{
struct prog_test_ref_kfunc *p;