netdev - Re: [PATCHv9 bpf-next 1/5] bpf: add a new bpf argument type ARG_CONST_MAP_PTR_OR

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Date:   Thu, 3 Sep 2020 17:15:37 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Jiri Benc <jbenc@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>, ast@...nel.org,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Andrii Nakryiko B <andrii.nakryiko@...il.com>
Subject: Re: [PATCHv9 bpf-next 1/5] bpf: add a new bpf argument type
 ARG_CONST_MAP_PTR_OR_NULL

Hi Daniel,

Sorry for the late reply. I was in PTO last few days.

On Fri, Aug 28, 2020 at 11:56:37PM +0200, Daniel Borkmann wrote:
> On 8/26/20 3:19 PM, Hangbin Liu wrote:
> > Add a new bpf argument type ARG_CONST_MAP_PTR_OR_NULL which could be
> > used when we want to allow NULL pointer for map parameter. The bpf helper
> > need to take care and check if the map is NULL when use this type.
> > 
> > Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> > ---
> > 
> > v9: merge the patch from [1] in to this series.
> > v1-v8: no this patch
> > 
> > [1] https://lore.kernel.org/bpf/20200715070001.2048207-1-liuhangbin@gmail.com/
> > ---
> >   include/linux/bpf.h   |  2 ++
> >   kernel/bpf/verifier.c | 23 ++++++++++++++++-------
> >   2 files changed, 18 insertions(+), 7 deletions(-)
> > 
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index a6131d95e31e..cb40a1281ea2 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -276,6 +276,7 @@ enum bpf_arg_type {
> >   	ARG_PTR_TO_ALLOC_MEM,	/* pointer to dynamically allocated memory */
> >   	ARG_PTR_TO_ALLOC_MEM_OR_NULL,	/* pointer to dynamically allocated memory or NULL */
> >   	ARG_CONST_ALLOC_SIZE_OR_ZERO,	/* number of allocated bytes requested */
> > +	ARG_CONST_MAP_PTR_OR_NULL,	/* const argument used as pointer to bpf_map or NULL */
> >   };
> >   /* type of values returned from helper functions */
> > @@ -369,6 +370,7 @@ enum bpf_reg_type {
> >   	PTR_TO_RDONLY_BUF_OR_NULL, /* reg points to a readonly buffer or NULL */
> >   	PTR_TO_RDWR_BUF,	 /* reg points to a read/write buffer */
> >   	PTR_TO_RDWR_BUF_OR_NULL, /* reg points to a read/write buffer or NULL */
> > +	CONST_PTR_TO_MAP_OR_NULL, /* reg points to struct bpf_map or NULL */
> 
> Why is this needed & where do you assign it? Also, if we were to use CONST_PTR_TO_MAP_OR_NULL
> then it's missing few things like rejection of arithmetic in adjust_ptr_min_max_vals(), handling
> in pruning logic etc.
> 
> Either way, given no helper currently returns CONST_PTR_TO_MAP_OR_NULL, the ARG_CONST_MAP_PTR_OR_NULL
> one should be sufficient, so I'd suggest to remove the CONST_PTR_TO_MAP_OR_NULL bits.

Sorry, I misunderstand the bpf_reg_type when added it.

Thanks for the comment. I will remove it.

> > -	} else if (arg_type == ARG_CONST_MAP_PTR) {
> > +	} else if (arg_type == ARG_CONST_MAP_PTR ||
> > +		   arg_type == ARG_CONST_MAP_PTR_OR_NULL) {
> >   		expected_type = CONST_PTR_TO_MAP;
> > -		if (type != expected_type)
> > +		if (register_is_null(reg) &&
> > +		    arg_type == ARG_CONST_MAP_PTR_OR_NULL)
> > +			/* final test in check_stack_boundary() */;
> 
> Where is that test in the code? Copy-paste leftover comment?

Yeah...  I will remove it.

Thanks
Hangbin