Re: [PATCH bpf-next v2 0/2] bpf: Add kfuncs for read-only string operations

[Viktor Malik <vmalik@redhat.com>]

On 9/27/24 03:37, Eduard Zingerman wrote:
> On Thu, 2024-09-26 at 09:29 +0200, Viktor Malik wrote:
>> Kernel contains highly optimised implementation of traditional string
>> operations. Expose them as kfuncs to allow BPF programs leverage the
>> kernel implementation instead of needing to reimplement the operations.
>>
>> These will be very helpful to bpftrace as it now needs to implement all
>> the string operations in LLVM IR.
> 
> Note that existing string related helpers take a pointer to a string
> and it's maximal length, namely:
> - bpf_strtol
> - bpf_strtoul
> - bpf_snprintf_btf
> - bpf_strncmp
> 
> The unbounded variants that are being exposed in this patch-set
> (like strcmp) are only safe to use if string is guaranteed to be null terminated.
> Verifier does not check this property at the moment (idk how easy/hard
> such analysis might be).
> 
> I'd suggest not to expose unbounded variants of string functions.

That's a great point, thanks. Let me remove the unbounded variants for
now, until we add the null-byte check to the verifier. The bounded
variants will still be useful to bpftrace so I'd love to have them added.

Viktor

> 
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