On 11/8/21 1:59 PM, Song Liu wrote:
>
>
>> On Nov 8, 2021, at 10:36 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>>
>>
>>
>> On 11/5/21 4:23 PM, Song Liu wrote:
>>> In some profiler use cases, it is necessary to map an address to the
>>> backing file, e.g., a shared library. bpf_find_vma helper provides a
>>> flexible way to achieve this. bpf_find_vma maps an address of a task to
>>> the vma (vm_area_struct) for this address, and feed the vma to an callback
>>> BPF function. The callback function is necessary here, as we need to
>>> ensure mmap_sem is unlocked.
>>>
>>> It is necessary to lock mmap_sem for find_vma. To lock and unlock mmap_sem
>>> safely when irqs are disable, we use the same mechanism as stackmap with
>>> build_id. Specifically, when irqs are disabled, the unlocked is postponed
>>> in an irq_work. Refactor stackmap.c so that the irq_work is shared among
>>> bpf_find_vma and stackmap helpers.
>>>
>>> Acked-by: Yonghong Song <yhs@xxxxxx>
>>> Tested-by: Hengqi Chen <hengqi.chen@xxxxxxxxx>
>>> Signed-off-by: Song Liu <songliubraving@xxxxxx>
>>> ---
>>
>> ...
>>
>>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>>> index dbc3ad07e21b6..cdb0fba656006 100644
>>> --- a/kernel/bpf/btf.c
>>> +++ b/kernel/bpf/btf.c
>>> @@ -6342,7 +6342,10 @@ const struct bpf_func_proto bpf_btf_find_by_name_kind_proto = {
>>> .arg4_type = ARG_ANYTHING,
>>> };
>>>
>>> -BTF_ID_LIST_GLOBAL_SINGLE(btf_task_struct_ids, struct, task_struct)
>>> +BTF_ID_LIST_GLOBAL(btf_task_struct_ids)
>>> +BTF_ID(struct, task_struct)
>>> +BTF_ID(struct, file)
>>> +BTF_ID(struct, vm_area_struct)
>>
>> $ nm -v vmlinux |grep -A3 btf_task_struct_ids
>> ffffffff82adfd9c R btf_task_struct_ids
>> ffffffff82adfda0 r __BTF_ID__struct__file__715
>> ffffffff82adfda4 r __BTF_ID__struct__vm_area_struct__716
>> ffffffff82adfda8 r bpf_skb_output_btf_ids
>>
>> KASAN thinks btf_task_struct_ids has 4 bytes only.
>
> I have KASAN enabled, but couldn't repro this issue. I think
> btf_task_struct_ids looks correct:
>
> nm -v vmlinux | grep -A3 -B1 btf_task_struct_ids
> ffffffff83cf8260 r __BTF_ID__struct__task_struct__1026
> ffffffff83cf8260 R btf_task_struct_ids
> ffffffff83cf8264 r __BTF_ID__struct__file__1027
> ffffffff83cf8268 r __BTF_ID__struct__vm_area_struct__1028
> ffffffff83cf826c r bpf_skb_output_btf_ids
>
> Did I miss something?
>
> Thanks,
> Song
>
I will release the syzbot bug, so that you can use its .config
Basically, we have
u32 btf_task_struct_ids[1];
xxxx = btf_task_struct_ids[2]; /* trap */
