On Apr 24, Jesper Dangaard Brouer wrote:
>
>
> On 23/04/2025 19.44, Lorenzo Bianconi wrote:
> > In the current implementation if the program is dev-bound to a specific
> > device, it will not be possible to perform XDP_REDIRECT into a DEVMAP
> > or CPUMAP even if the program is running in the driver NAPI context and
> > it is not attached to any map entry. This seems in contrast with the
> > explanation available in bpf_prog_map_compatible routine.
> > Fix the issue introducing __bpf_prog_map_compatible utility routine in
> > order to avoid bpf_prog_is_dev_bound() check running bpf_check_tail_call()
> > at program load time (bpf_prog_select_runtime()).
> > Continue forbidding to attach a dev-bound program to XDP maps
> > (BPF_MAP_TYPE_PROG_ARRAY, BPF_MAP_TYPE_DEVMAP and BPF_MAP_TYPE_CPUMAP).
> >
> > Fixes: 3d76a4d3d4e59 ("bpf: XDP metadata RX kfuncs")
> > Signed-off-by: Lorenzo Bianconi<lorenzo@xxxxxxxxxx>
> > ---
> > Changes in v2:
> > - Introduce __bpf_prog_map_compatible() utility routine in order to skip
> > bpf_prog_is_dev_bound check in bpf_check_tail_call()
> > - Extend xdp_metadata selftest
> > - Link to v1:https://lore.kernel.org/r/20250422-xdp-prog-bound-fix-v1-1-0b581fa186fe@xxxxxxxxxx
> > ---
> > kernel/bpf/core.c | 27 +++++++++++++---------
> > .../selftests/bpf/prog_tests/xdp_metadata.c | 22 +++++++++++++++++-
> > tools/testing/selftests/bpf/progs/xdp_metadata.c | 13 +++++++++++
> > 3 files changed, 50 insertions(+), 12 deletions(-)
> >
> > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > index ba6b6118cf504041278d05417c4212d57be6fca0..a3e571688421196c3ceaed62b3b59b62a0258a8c 100644
> > --- a/kernel/bpf/core.c
> > +++ b/kernel/bpf/core.c
> > @@ -2358,8 +2358,8 @@ static unsigned int __bpf_prog_ret0_warn(const void *ctx,
> > return 0;
> > }
> > -bool bpf_prog_map_compatible(struct bpf_map *map,
> > - const struct bpf_prog *fp)
> > +static bool __bpf_prog_map_compatible(struct bpf_map *map,
> > + const struct bpf_prog *fp)
> > {
> > enum bpf_prog_type prog_type = resolve_prog_type(fp);
> > bool ret;
> > @@ -2368,14 +2368,6 @@ bool bpf_prog_map_compatible(struct bpf_map *map,
> > if (fp->kprobe_override)
> > return false;
> > - /* XDP programs inserted into maps are not guaranteed to run on
> > - * a particular netdev (and can run outside driver context entirely
> > - * in the case of devmap and cpumap). Until device checks
> > - * are implemented, prohibit adding dev-bound programs to program maps.
> > - */
> > - if (bpf_prog_is_dev_bound(aux))
> > - return false;
> > -
> > spin_lock(&map->owner.lock);
> > if (!map->owner.type) {
> > /* There's no owner yet where we could check for
> > @@ -2409,6 +2401,19 @@ bool bpf_prog_map_compatible(struct bpf_map *map,
> > return ret;
> > }
> > +bool bpf_prog_map_compatible(struct bpf_map *map, const struct bpf_prog *fp)
> > +{
> > + /* XDP programs inserted into maps are not guaranteed to run on
> > + * a particular netdev (and can run outside driver context entirely
> > + * in the case of devmap and cpumap). Until device checks
> > + * are implemented, prohibit adding dev-bound programs to program maps.
> > + */
> > + if (bpf_prog_is_dev_bound(fp->aux))
> > + return false;
> > +
> > + return __bpf_prog_map_compatible(map, fp);
> > +}
> > +
> > static int bpf_check_tail_call(const struct bpf_prog *fp)
> > {
> > struct bpf_prog_aux *aux = fp->aux;
> > @@ -2421,7 +2426,7 @@ static int bpf_check_tail_call(const struct bpf_prog *fp)
> > if (!map_type_contains_progs(map))
> > continue;
> > - if (!bpf_prog_map_compatible(map, fp)) {
> > + if (!__bpf_prog_map_compatible(map, fp)) {
> > ret = -EINVAL;
> > goto out;
> > }
>
> Does this change allow us to have a dev_bound BPF-prog that have
> tail-call BPF-progs that are not dev_bound?
>
> The use-case is a dev_bound BPF-prog that reads e.g. HW vlan, store this in
> data_meta (or a per CPU array), and then tail-calls another BPF-prog that
> reads the data stored (from data_meta area). Maybe this is already supported
> before?
I think this patch allows a dev-bound program to run hw-metadata kfuncs and
perform XDP_REDIRECT into a prog_array but you will not be able to read these
info via hw-metadata kfuncs in a tail-call program since just dev-bound
programs are currently allowed to do that (and you can't insert a dev-bound
programs in BPF_MAP_TYPE_PROG_ARRAY).
Regards,
Lorenzo
>
> --Jesper
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