Re: [PATCH bpf-next v5 3/6] bpf: Remove is_valid_bpf_tramp_flags()

[Xu Kuohai <xukuohai@huawei.com>]

On 5/26/2022 6:12 PM, Mark Rutland wrote:
> On Thu, May 26, 2022 at 05:45:25PM +0800, Xu Kuohai wrote:
>> On 5/25/2022 9:45 PM, Mark Rutland wrote:
>>> On Wed, May 18, 2022 at 09:16:35AM -0400, Xu Kuohai wrote:
>>>> BPF_TRAM_F_XXX flags are not used by user code and are almost constant
>>>> at compile time, so run time validation is a bit overkill. Remove
>>>> is_valid_bpf_tramp_flags() and add some usage comments.
>>>>
>>>> Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
>>>> Acked-by: Song Liu <songliubraving@fb.com>
>>>
>>> Am I right in thinking this is independent of the arm64-specific bits, and
>>> could be taken on its own now?
>>>
>>
>> Currenly is_valid_bpf_tramp_flags() is defined in x86 and called before
>> bpf trampoline is constructed. The check logic is irrelevant to the
>> architecture code. So we also need to call this function on arm64. But
>> as Alexei pointed out, the check is not requried, so it's better to
>> remove it before adding bpf trampoline to arm64.
> 
> Cool. So this patch could be merged now, even if the rest of the series needs
> more work?
> 

Agree with you, thanks.

> Thanks,
> Mark.
> 
>>>> ---
>>>>  arch/x86/net/bpf_jit_comp.c | 20 --------------------
>>>>  kernel/bpf/bpf_struct_ops.c |  3 +++
>>>>  kernel/bpf/trampoline.c     |  3 +++
>>>>  3 files changed, 6 insertions(+), 20 deletions(-)
>>>>
>>>> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
>>>> index a2b6d197c226..7698ef3b4821 100644
>>>> --- a/arch/x86/net/bpf_jit_comp.c
>>>> +++ b/arch/x86/net/bpf_jit_comp.c
>>>> @@ -1922,23 +1922,6 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
>>>>  	return 0;
>>>>  }
>>>>  
>>>> -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;
>>>> -}
>>>> -
>>>>  /* Example:
>>>>   * __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev);
>>>>   * its 'struct btf_func_model' will be nr_args=2
>>>> @@ -2017,9 +2000,6 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
>>>>  	if (nr_args > 6)
>>>>  		return -ENOTSUPP;
>>>>  
>>>> -	if (!is_valid_bpf_tramp_flags(flags))
>>>> -		return -EINVAL;
>>>> -
>>>>  	/* Generated trampoline stack layout:
>>>>  	 *
>>>>  	 * RBP + 8         [ return address  ]
>>>> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
>>>> index d9a3c9207240..0572cc5aeb28 100644
>>>> --- a/kernel/bpf/bpf_struct_ops.c
>>>> +++ b/kernel/bpf/bpf_struct_ops.c
>>>> @@ -341,6 +341,9 @@ int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks,
>>>>  
>>>>  	tlinks[BPF_TRAMP_FENTRY].links[0] = link;
>>>>  	tlinks[BPF_TRAMP_FENTRY].nr_links = 1;
>>>> +	/* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,
>>>> +	 * and it must be used alone.
>>>> +	 */
>>>>  	flags = model->ret_size > 0 ? BPF_TRAMP_F_RET_FENTRY_RET : 0;
>>>>  	return arch_prepare_bpf_trampoline(NULL, image, image_end,
>>>>  					   model, flags, tlinks, NULL);
>>>> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
>>>> index 93c7675f0c9e..bd3f2e673874 100644
>>>> --- a/kernel/bpf/trampoline.c
>>>> +++ b/kernel/bpf/trampoline.c
>>>> @@ -358,6 +358,9 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
>>>>  
>>>>  	if (tlinks[BPF_TRAMP_FEXIT].nr_links ||
>>>>  	    tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links)
>>>> +		/* NOTE: BPF_TRAMP_F_RESTORE_REGS and BPF_TRAMP_F_SKIP_FRAME
>>>> +		 * should not be set together.
>>>> +		 */
>>>>  		flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;
>>>>  
>>>>  	if (ip_arg)
>>>> -- 
>>>> 2.30.2
>>>>
>>> .
>>
> .


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