On Wed, 19 Aug 2020 at 21:13, Yonghong Song <yhs@xxxxxx> wrote:
>
>
>
> On 8/19/20 2:24 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 | 40 ++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 40 insertions(+)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index b6ccfce3bf4c..47f9b94bb9d4 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -3872,6 +3872,38 @@ static int int_ptr_type_to_size(enum bpf_arg_type type)
> > return -EINVAL;
> > }
> >
> > +static int override_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:
> > + switch (*arg_type) {
> > + case ARG_PTR_TO_MAP_VALUE:
> > + *arg_type = ARG_PTR_TO_SOCKET;
> > + break;
> > + case ARG_PTR_TO_MAP_VALUE_OR_NULL:
> > + *arg_type = ARG_PTR_TO_SOCKET_OR_NULL;
> > + break;
> > + default:
> > + 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 +3936,14 @@ 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) {
>
> We probably do not need ARG_PTR_TO_UNINIT_MAP_VALUE here.
>
> Do we need ARG_PTR_TO_MAP_VALUE_OR_NULL? bpf_map_update_elem arg type
> is ARG_PTR_TO_MAP_VALUE.
I did this to be consistent: in a single function definition you
either get the map specific
types or the regular semantics. You don't get to mix and match them.
For the same
reason I included ARG_PTR_TO_UNINIT_MAP_VALUE: the semantics don't make
sense for sockmap, so a function using this doesn't make sense either.
>
> > + err = override_map_arg_type(env, meta, &arg_type);
> > + 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
