netdev - [PATCH RFC bpf-next 14/15] bpf, verifier: Track when data

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Message-Id: <20251124-skb-meta-safeproof-netdevs-rx-only-v1-14-8978f5054417@cloudflare.com>
Date: Mon, 24 Nov 2025 17:28:50 +0100
From: Jakub Sitnicki <jakub@...udflare.com>
To: bpf@...r.kernel.org
Cc: netdev@...r.kernel.org, kernel-team@...udflare.com, 
 Martin KaFai Lau <martin.lau@...ux.dev>
Subject: [PATCH RFC bpf-next 14/15] bpf, verifier: Track when data_meta
 pointer is loaded

Introduce PA_F_DATA_META_LOAD flag to track when a BPF program loads the
skb->data_meta pointer.

This information will be used by gen_prologue() to handle cases where there
is a gap between metadata end and skb->data, requiring metadata to be
realigned.

Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 include/linux/bpf_verifier.h | 1 +
 kernel/bpf/verifier.c        | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 42ce94ce96ba..fa330e4dc14a 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -639,6 +639,7 @@ enum priv_stack_mode {
 
 enum packet_access_flags {
 	PA_F_DIRECT_WRITE = BIT(0),
+	PA_F_DATA_META_LOAD = BIT(1),
 };
 
 struct bpf_subprog_info {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index bb4e70913ab4..32989e29a5e1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6160,6 +6160,10 @@ static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off,
 		} else {
 			env->insn_aux_data[insn_idx].ctx_field_size = info->ctx_field_size;
 		}
+
+		if (base_type(info->reg_type) == PTR_TO_PACKET_META)
+			env->seen_packet_access |= PA_F_DATA_META_LOAD;
+
 		/* remember the offset of last byte accessed in ctx */
 		if (env->prog->aux->max_ctx_offset < off + size)
 			env->prog->aux->max_ctx_offset = off + size;

-- 
2.43.0