On Thu, Jul 16, 2020 at 12:28:16AM +0200, Daniel Borkmann wrote:
> On 7/15/20 9:00 AM, 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 <liuhang...@gmail.com>
>
> Is this patch to be merged into the set in [0] for passing NULL ex_map as
> discussed?
> Seems you sent out two incomplete sets?
>
> [0]
> https://lore.kernel.org/bpf/20200709013008.3900892-1-liuhang...@gmail.com/T/#m99a8fa8ffe79d5f00d305c0800ad3abe619294f2
Yes, I did it by intend. I thought these two should be consider as
different feature. So I'd prefer post them separately. Once both
patches are merged, I will post a followup patch to add the NULL pointer
support to xdp multicast helper.
>
> > ---
> > include/linux/bpf.h | 1 +
> > kernel/bpf/verifier.c | 11 ++++++++---
> > 2 files changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index c67c88ad35f8..9d4dbef3c943 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -253,6 +253,7 @@ 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 */
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 3c1efc9d08fd..d3551a19853a 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -3849,9 +3849,13 @@ static int check_func_arg(struct bpf_verifier_env
> > *env, u32 arg,
> > expected_type = SCALAR_VALUE;
> > if (type != expected_type)
> > goto err_type;
> > - } 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() */;
> > + else if (type != expected_type)
> > goto err_type;
> > } else if (arg_type == ARG_PTR_TO_CTX ||
> > arg_type == ARG_PTR_TO_CTX_OR_NULL) {
> > @@ -3957,7 +3961,8 @@ static int check_func_arg(struct bpf_verifier_env
> > *env, u32 arg,
> > return -EFAULT;
> > }
> > - if (arg_type == ARG_CONST_MAP_PTR) {
> > + if (arg_type == ARG_CONST_MAP_PTR ||
> > + (arg_type == ARG_CONST_MAP_PTR_OR_NULL && !register_is_null(reg))) {
> > /* bpf_map_xxx(map_ptr) call: remember that map_ptr */
> > meta->map_ptr = reg->map_ptr;
>
> I would probably have the semantics a bit different in the sense that I would
> update meta->map_ptr to the last ARG_CONST_MAP_PTR, meaning:
>
> meta->map_ptr = register_is_null(reg) ? NULL : reg->map_ptr;
Thanks for the suggestion. I will update it.
>
> > } else if (arg_type == ARG_PTR_TO_MAP_KEY) {
> >
>
> In combination with the set, this also needs test_verifier selftests in order
> to
> exercise BPF insn snippets for the good & [expected] bad case.
OK, I will add a test for this.
Thanks
Hangbin
