Re: [PATCH bpf-next 1/2] bpf: add hardware timestamp field to __sk_buff

On 03.09.2021 09:22, Daniel Borkmann wrote:

On 9/3/21 12:15 AM, Vadim Fedorenko wrote:

quoted

BPF programs may want to know hardware timestamps if NIC supports
such timestamping.

Expose this data as hwtstamp field of __sk_buff the same way as
gso_segs/gso_size.

Also update BPF_PROG_TEST_RUN tests of the feature.

Signed-off-by: Vadim Fedorenko <redacted>
---
  include/uapi/linux/bpf.h       |  2 ++
  net/core/filter.c              | 11 +++++++++++
  tools/include/uapi/linux/bpf.h |  2 ++
  3 files changed, 15 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 791f31dd0abe..c7d05b49f557 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -5284,6 +5284,8 @@ struct __sk_buff {

      __u32 gso_segs;
      __bpf_md_ptr(struct bpf_sock *, sk);
      __u32 gso_size;
+    __u32 padding;        /* Padding, future use. */

nit, instead of explicit padding field, just use: __u32 :32;

Also please add test_verifier coverage for this in BPF selftests, meaning,
the expectation would be in case someone tries to access the padding field
with this patch that we get a 'bpf verifier is misconfigured' error given
it would have no bpf_convert_ctx_access() translation. But it would be overall
better to add this to bpf_skb_is_valid_access(), so we can reject access to
the padding area right there instead.

Thanks Daniel, I will update it in v2

quoted

+    __u64 hwtstamp;
  };
  struct bpf_tunnel_key {

diff --git a/net/core/filter.c b/net/core/filter.c
index 2e32cee2c469..1d8f8494d325 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c

@@ -8884,6 +8884,17 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type 

type,
                        si->dst_reg, si->src_reg,
                        offsetof(struct sk_buff, sk));
          break;
+    case offsetof(struct __sk_buff, hwtstamp):
+        BUILD_BUG_ON(sizeof_field(struct skb_shared_hwtstamps, hwtstamp) != 8);
+        BUILD_BUG_ON(offsetof(struct skb_shared_hwtstamps, hwtstamp) != 0);
+
+        insn = bpf_convert_shinfo_access(si, insn);
+        *insn++ = BPF_LDX_MEM(BPF_DW,
+                      si->dst_reg, si->dst_reg,
+                      bpf_target_off(struct skb_shared_info,
+                             hwtstamps, 8,
+                             target_size));
+        break;
      }
      return insn - insn_buf;

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 791f31dd0abe..c7d05b49f557 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h

@@ -5284,6 +5284,8 @@ struct __sk_buff {

      __u32 gso_segs;
      __bpf_md_ptr(struct bpf_sock *, sk);
      __u32 gso_size;
+    __u32 padding;        /* Padding, future use. */
+    __u64 hwtstamp;
  };
  struct bpf_tunnel_key {