From: Dave Marchevsky <davemarchevsky@meta.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Delyan Kratunov <delyank@meta.com>
Subject: Re: [PATCH bpf-next v2 10/25] bpf: Introduce local kptrs
Date: Tue, 25 Oct 2022 12:27:58 -0400 [thread overview]
Message-ID: <d147dca1-4b8b-338e-103c-9ecdb476f06d@meta.com> (raw)
In-Reply-To: <20221020004837.qclzg6pgrqamcn7e@apollo>
On 10/19/22 8:48 PM, Kumar Kartikeya Dwivedi wrote:
> On Wed, Oct 19, 2022 at 10:45:22PM IST, Dave Marchevsky wrote:
>> On 10/13/22 2:22 AM, Kumar Kartikeya Dwivedi wrote:
>>> Introduce the idea of local kptrs, i.e. PTR_TO_BTF_ID that point to a
>>> type in program BTF. This is indicated by the presence of MEM_TYPE_LOCAL
>>> type tag in reg->type to avoid having to check btf_is_kernel when trying
>>> to match argument types in helpers.
>>>
>>> For now, these local kptrs will always be referenced in verifier
>>> context, hence ref_obj_id == 0 for them is a bug. It is allowed to write
>>> to such objects, as long fields that are special are not touched
>>> (support for which will be added in subsequent patches).
>>>
>>> No PROBE_MEM handling is hence done since they can never be in an
>>> undefined state, and their lifetime will always be valid.
>>>
>>> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
>>> ---
[...]
>>
>>
>> more re: passing entire reg state to btf_struct access:
>>
>> In the next patch in the series ("bpf: Recognize bpf_{spin_lock,list_head,list_node} in local kptrs")
>> you do btf_find_struct_meta(btf, reg->btf_id). I see why you couldn't use 't'
>> that's passed in here / elsewhere since you need the btf_id for meta lookup.
>> Perhaps 'btf_type *t' param can be changed to btf_id, eliminating the need
>> to pass 'reg'.
>>
>> Alternatively, since we're already passing reg->btf and result of
>> btf_type_by_id(reg->btf, reg->btf_id), seems like btf_struct_access
>> maybe is tied closely enough to reg state that passing reg state
>> directly and getting rid of extraneous args is cleaner.
>>
>
> So Alexei actually suggested dropping both btf and type arguments and simply
> pass in the register and get it from there.
>
> But one call site threw a wrench in the plan:
>
> check_ptr_to_map_access -> btf_struct_access
>
> Here, it passes it's own btf and type to simulate access to a map. Maybe I
> should be creating a dummy register on stack and make it work like that for this
> particular case? Otherwise all other callers pass in what they have from reg.
Ah, sorry for missing that. Personally I'm not a fan of dummy register on the
stack. Then if btf_struct_access starts using some reg state that wasn't
populated in the dummy reg it will be confusing.
next prev parent reply other threads:[~2022-10-25 16:28 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-13 6:22 [PATCH bpf-next v2 00/25] Local kptrs, BPF linked lists Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 01/25] bpf: Document UAPI details for special BPF types Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 02/25] bpf: Allow specifying volatile type modifier for kptrs Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 03/25] bpf: Clobber stack slot when writing over spilled PTR_TO_BTF_ID Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 04/25] bpf: Fix slot type check in check_stack_write_var_off Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 05/25] bpf: Drop reg_type_may_be_refcounted_or_null Kumar Kartikeya Dwivedi
2022-10-19 16:04 ` Dave Marchevsky
2022-10-13 6:22 ` [PATCH bpf-next v2 06/25] bpf: Refactor kptr_off_tab into fields_tab Kumar Kartikeya Dwivedi
2022-10-19 1:35 ` Alexei Starovoitov
2022-10-19 5:42 ` Kumar Kartikeya Dwivedi
2022-10-19 15:54 ` Alexei Starovoitov
2022-10-19 23:57 ` Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 07/25] bpf: Consolidate spin_lock, timer management " Kumar Kartikeya Dwivedi
2022-10-19 1:40 ` Alexei Starovoitov
2022-10-19 5:43 ` Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 08/25] bpf: Refactor map->off_arr handling Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 09/25] bpf: Support bpf_list_head in map values Kumar Kartikeya Dwivedi
2022-10-19 1:59 ` Alexei Starovoitov
2022-10-19 5:48 ` Kumar Kartikeya Dwivedi
2022-10-19 15:57 ` Alexei Starovoitov
2022-10-19 23:59 ` Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 10/25] bpf: Introduce local kptrs Kumar Kartikeya Dwivedi
2022-10-19 17:15 ` Dave Marchevsky
2022-10-20 0:48 ` Kumar Kartikeya Dwivedi
2022-10-25 16:27 ` Dave Marchevsky [this message]
2022-10-25 18:11 ` Kumar Kartikeya Dwivedi
2022-10-25 16:32 ` Dave Marchevsky
2022-10-25 18:11 ` Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 11/25] bpf: Recognize bpf_{spin_lock,list_head,list_node} in " Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 12/25] bpf: Verify ownership relationships for owning types Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 13/25] bpf: Support locking bpf_spin_lock in local kptr Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 14/25] bpf: Allow locking bpf_spin_lock global variables Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 15/25] bpf: Rewrite kfunc argument handling Kumar Kartikeya Dwivedi
2022-10-13 13:48 ` kernel test robot
2022-10-13 6:22 ` [PATCH bpf-next v2 16/25] bpf: Drop kfunc bits from btf_check_func_arg_match Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 17/25] bpf: Support constant scalar arguments for kfuncs Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 18/25] bpf: Teach verifier about non-size constant arguments Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 19/25] bpf: Introduce bpf_kptr_new Kumar Kartikeya Dwivedi
2022-10-19 2:31 ` Alexei Starovoitov
2022-10-19 5:58 ` Kumar Kartikeya Dwivedi
2022-10-19 16:31 ` Alexei Starovoitov
2022-10-20 0:44 ` Kumar Kartikeya Dwivedi
2022-10-20 1:11 ` Alexei Starovoitov
2022-10-13 6:22 ` [PATCH bpf-next v2 20/25] bpf: Introduce bpf_kptr_drop Kumar Kartikeya Dwivedi
2022-10-13 6:22 ` [PATCH bpf-next v2 21/25] bpf: Permit NULL checking pointer with non-zero fixed offset Kumar Kartikeya Dwivedi
2022-10-13 6:23 ` [PATCH bpf-next v2 22/25] bpf: Introduce single ownership BPF linked list API Kumar Kartikeya Dwivedi
2022-10-25 17:45 ` Dave Marchevsky
2022-10-25 19:00 ` Kumar Kartikeya Dwivedi
2022-10-13 6:23 ` [PATCH bpf-next v2 23/25] libbpf: Add support for private BSS map section Kumar Kartikeya Dwivedi
2022-10-18 4:03 ` Andrii Nakryiko
2022-10-13 6:23 ` [PATCH bpf-next v2 24/25] selftests/bpf: Add __contains macro to bpf_experimental.h Kumar Kartikeya Dwivedi
2022-10-13 6:23 ` [PATCH bpf-next v2 25/25] selftests/bpf: Add BPF linked list API tests Kumar Kartikeya Dwivedi
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