[PATCH bpf-next 1/2] bpf: xdp: allow offloads to store into rx_queue_index

[Jakub Kicinski]

It's fairly easy for offloaded XDP programs to select the RX queue
packets go to.  We need a way of expressing this in the software.
Allow write to the rx_queue_index field of struct xdp_md for
device-bound programs.

Skip convert_ctx_access callback entirely for offloads.

Signed-off-by: Jakub Kicinski <jakub.kicin...@netronome.com>
Reviewed-by: Quentin Monnet <quentin.mon...@netronome.com>
---
 include/linux/bpf.h   | 2 +-
 kernel/bpf/verifier.c | 2 +-
 net/core/filter.c     | 9 ++++++++-
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 321969da67b7..a38e474bf7ee 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -627,7 +627,7 @@ bool bpf_offload_dev_match(struct bpf_prog *prog, struct 
bpf_map *map);
 #if defined(CONFIG_NET) && defined(CONFIG_BPF_SYSCALL)
 int bpf_prog_offload_init(struct bpf_prog *prog, union bpf_attr *attr);
 
-static inline bool bpf_prog_is_dev_bound(struct bpf_prog_aux *aux)
+static inline bool bpf_prog_is_dev_bound(const struct bpf_prog_aux *aux)
 {
        return aux->offload_requested;
 }
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d5e1a6c4165d..d92d9c37affd 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5215,7 +5215,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env 
*env)
                }
        }
 
-       if (!ops->convert_ctx_access)
+       if (!ops->convert_ctx_access || bpf_prog_is_dev_bound(env->prog->aux))
                return 0;
 
        insn = env->prog->insnsi + delta;
diff --git a/net/core/filter.c b/net/core/filter.c
index cf0d27acf1d1..2336b90e8b26 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4911,8 +4911,15 @@ static bool xdp_is_valid_access(int off, int size,
                                const struct bpf_prog *prog,
                                struct bpf_insn_access_aux *info)
 {
-       if (type == BPF_WRITE)
+       if (type == BPF_WRITE) {
+               if (bpf_prog_is_dev_bound(prog->aux)) {
+                       switch (off) {
+                       case offsetof(struct xdp_md, rx_queue_index):
+                               return __is_valid_xdp_access(off, size);
+                       }
+               }
                return false;
+       }
 
        switch (off) {
        case offsetof(struct xdp_md, data):
-- 
2.17.0