On 8/21/24 19:02, Alexei Starovoitov wrote:
On Fri, Aug 16, 2024 at 6:24 AM Juntong Deng <juntong.deng@xxxxxxxxxxx> wrote:Currently the non-zero offset pointer constraint for KF_TRUSTED_ARGS kfuncs has been relaxed in commit 605c96997d89 ("bpf: relax zero fixed offset constraint on KF_TRUSTED_ARGS/KF_RCU"), which means that non-zero offset does not affect whether a pointer is valid. But currently we still cannot pass non-zero offset pointers to KF_ACQUIRE kfuncs. This is because KF_ACQUIRE kfuncs requires strict type matching, but non-zero offset does not change the type of pointer, which causes the ebpf program to be rejected by the verifier. This can cause some problems, one example is that bpf_skb_peek_tail kfunc [0] cannot be implemented by just passing in non-zero offset pointers. This patch makes KF_ACQUIRE kfuncs not require strict type matching on non-zero offset pointers. [0]: https://lore.kernel.org/bpf/AM6PR03MB5848CA39CB4B7A4397D380B099B12@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ Signed-off-by: Juntong Deng <juntong.deng@xxxxxxxxxxx> --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ebec74c28ae3..3a14002d24a0 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11484,7 +11484,7 @@ static int process_kf_arg_ptr_to_btf_id(struct bpf_verifier_env *env, * btf_struct_ids_match() to walk the struct at the 0th offset, and * resolve types. */ - if (is_kfunc_acquire(meta) || + if ((is_kfunc_acquire(meta) && !reg->off) ||Agree that relaxing is fine and calling acquire kfunc like: bpf_kfunc_nested_acquire_test(&sk->sk_write_queue); should be allowed, but above check is strange, since if offsetof(&sk_write_queue) == 0 it will disallow calling a kfunc. I mean if the field is the first in the outer struct this condition will force strict type match which will fail, right? So should we remove the above is_kfunc_acquire() check instead? pw-bot: cr
I agree that if strict type matching is not required for both zero offset and non-zero pointers, then we can remove the strict type matching for KF_ACQUIRE kfuncs. I sent the version 2 patch set: https://lore.kernel.org/bpf/AM6PR03MB5848FD2BD89BF0B6B5AA3B4C99952@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/T/#t
