On Thu, 20 Aug 2020 at 17:10, Yonghong Song <yhs@xxxxxx> wrote:
>
>
>
> On 8/20/20 6:57 AM, Lorenz Bauer wrote:
> > The verifier assumes that map values are simple blobs of memory, and
> > therefore treats ARG_PTR_TO_MAP_VALUE, etc. as such. However, there are
> > map types where this isn't true. For example, sockmap and sockhash store
> > sockets. In general this isn't a big problem: we can just
> > write helpers that explicitly requests PTR_TO_SOCKET instead of
> > ARG_PTR_TO_MAP_VALUE.
> >
> > The one exception are the standard map helpers like map_update_elem,
> > map_lookup_elem, etc. Here it would be nice we could overload the
> > function prototype for different kinds of maps. Unfortunately, this
> > isn't entirely straight forward:
> > We only know the type of the map once we have resolved meta->map_ptr
> > in check_func_arg. This means we can't swap out the prototype
> > in check_helper_call until we're half way through the function.
> >
> > Instead, modify check_func_arg to treat ARG_PTR_TO_MAP_VALUE* to
> > mean "the native type for the map" instead of "pointer to memory"
> > for sockmap and sockhash. This means we don't have to modify the
> > function prototype at all
> >
> > Signed-off-by: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>
> > ---
> > kernel/bpf/verifier.c | 37 +++++++++++++++++++++++++++++++++++++
> > 1 file changed, 37 insertions(+)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index b6ccfce3bf4c..24feec515d3e 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -3872,6 +3872,35 @@ static int int_ptr_type_to_size(enum bpf_arg_type type)
> > return -EINVAL;
> > }
> >
> > +static int resolve_map_arg_type(struct bpf_verifier_env *env,
> > + const struct bpf_call_arg_meta *meta,
> > + enum bpf_arg_type *arg_type)
> > +{
> > + if (!meta->map_ptr) {
> > + /* kernel subsystem misconfigured verifier */
> > + verbose(env, "invalid map_ptr to access map->type\n");
> > + return -EACCES;
> > + }
> > +
> > + switch (meta->map_ptr->map_type) {
> > + case BPF_MAP_TYPE_SOCKMAP:
> > + case BPF_MAP_TYPE_SOCKHASH:
> > + if (*arg_type == ARG_PTR_TO_MAP_VALUE) {
> > + *arg_type = ARG_PTR_TO_SOCKET;
> > + } else if (*arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL) {
> > + *arg_type = ARG_PTR_TO_SOCKET_OR_NULL;
>
> Is this *arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL possible with
> current implementation?
No, the only user is bpf_sk_storage_get and friends which requires
BPF_MAP_TYPE_SK_STORAGE.
I seemed to make sense to map ARG_PTR_TO_MAP_VALUE_OR_NULL, but I can
remove it as
well if you prefer. Do you think this is dangerous?
>
> If not, we can remove this "else if" and return -EINVAL, right?
>
> > + } else {
> > + verbose(env, "invalid arg_type for sockmap/sockhash\n");
> > + return -EINVAL;
> > + }
> > + break;
> > +
> > + default:
> > + break;
> > + }
> > + return 0;
> > +}
> > +
> > static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> > struct bpf_call_arg_meta *meta,
> > const struct bpf_func_proto *fn)
> > @@ -3904,6 +3933,14 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> > return -EACCES;
> > }
> >
> > + if (arg_type == ARG_PTR_TO_MAP_VALUE ||
> > + arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE ||
> > + arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL) {
> > + err = resolve_map_arg_type(env, meta, &arg_type);
>
> I am okay with this to cover all MAP_VALUE types with func
> name resolve_map_arg_type as a generic helper.
>
> > + if (err)
> > + return err;
> > + }
> > +
> > if (arg_type == ARG_PTR_TO_MAP_KEY ||
> > arg_type == ARG_PTR_TO_MAP_VALUE ||
> > arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE ||
> >
--
Lorenz Bauer | Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
www.cloudflare.com
