Re: [RFC PATCH v1 02/10] bpf: widen dynptr size/offset to 64 bit

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 10/3/25 19:40, Eduard Zingerman wrote:
> On Fri, 2025-10-03 at 17:04 +0100, Mykyta Yatsenko wrote:
>> From: Mykyta Yatsenko <yatsenko@meta.com>
>>
>> Dynptr currently caps size and offset at 24 bits, which isn’t sufficient
>> for file-backed use cases; even 32 bits can be limiting. Refactor dynptr
>> helpers/kfuncs to use 64-bit size and offset, ensuring consistency
>> across the APIs.
>>
>> This change does not affect internals of xdp, skb or other dynptrs,
>> which continue to behave as before.
>>
>> The widening enables large-file access support via dynptr, implemented
>> in the next patches.
> Maybe add a note here that this change does not break binary
> compatibility with BPF programs compiled for older kernels?
>
>> Signed-off-by: Mykyta Yatsenko <yatsenko@meta.com>
>> ---
> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
>
> [...]
>
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index 8f23f5273bab..7cc4f2e05ed2 100644
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -3372,13 +3372,13 @@ typedef int (*copy_fn_t)(void *dst, const void *src, u32 size, struct task_struc
>>    * direct calls into all the specific callback implementations
>>    * (copy_user_data_sleepable, copy_user_data_nofault, and so on)
>>    */
>> -static __always_inline int __bpf_dynptr_copy_str(struct bpf_dynptr *dptr, u32 doff, u32 size,
>> +static __always_inline int __bpf_dynptr_copy_str(struct bpf_dynptr *dptr, u64 doff, u64 size,
>>   						 const void *unsafe_src,
>>   						 copy_fn_t str_copy_fn,
> The definition for copy_fn_t looks like:
>
>    typedef int (*copy_fn_t)(void *dst, const void *src, u32 size, struct task_struct *tsk);
>
> should we change it to use u64 as well? Probably does not matter.
This callback does not work with dynptr, that's why I did not convert it.
>
>>   						 struct task_struct *tsk)
>>   {
>>   	struct bpf_dynptr_kern *dst;
>> -	u32 chunk_sz, off;
>> +	u64 chunk_sz, off;
>>   	void *dst_slice;
>>   	int cnt, err;
>>   	char buf[256];
> [...]