Re: [PATCH bpf-next v4 3/6] bpf: Move is_valid_bpf_tramp_flags() to the public trampoline code

[Xu Kuohai]

On 5/17/2022 11:53 PM, Alexei Starovoitov wrote:
> On Tue, May 17, 2022 at 03:18:35AM -0400, Xu Kuohai wrote:
>>  
>> +static bool is_valid_bpf_tramp_flags(unsigned int flags)
>> +{
>> +	if ((flags & BPF_TRAMP_F_RESTORE_REGS) &&
>> +	    (flags & BPF_TRAMP_F_SKIP_FRAME))
>> +		return false;
>> +
>> +	/* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,
>> +	 * and it must be used alone.
>> +	 */
>> +	if ((flags & BPF_TRAMP_F_RET_FENTRY_RET) &&
>> +	    (flags & ~BPF_TRAMP_F_RET_FENTRY_RET))
>> +		return false;
>> +
>> +	return true;
>> +}
>> +
>> +int bpf_prepare_trampoline(struct bpf_tramp_image *tr, void *image,
>> +			   void *image_end, const struct btf_func_model *m,
>> +			   u32 flags, struct bpf_tramp_links *tlinks,
>> +			   void *orig_call)
>> +{
>> +	if (!is_valid_bpf_tramp_flags(flags))
>> +		return -EINVAL;
>> +
>> +	return arch_prepare_bpf_trampoline(tr, image, image_end, m, flags,
>> +					   tlinks, orig_call);
>> +}
> 
> It's an overkill to introduce a new helper function just to validate
> flags that almost compile time constants.
> The flags are not user supplied.
> Please move /* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops ... */
> comment to bpf_struct_ops.c right before it calls arch_prepare_bpf_trampoline()
> And add a comment to trampoline.c saying that BPF_TRAMP_F_RESTORE_REGS
> and BPF_TRAMP_F_SKIP_FRAME should not be set together.
> We could add a warn_on there or in arch code, but feels like overkill.
> .

OK, will fix in next version.