netdev - [PATCH RFC bpf-next 12/15] bpf, verifier: Turn seen_direct

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Message-Id: <20251124-skb-meta-safeproof-netdevs-rx-only-v1-12-8978f5054417@cloudflare.com>
Date: Mon, 24 Nov 2025 17:28:48 +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 12/15] bpf, verifier: Turn seen_direct_write
 flag into a bitmap

Convert seen_direct_write from a boolean to a bitmap (seen_packet_access)
in preparation for tracking additional packet access patterns.

No functional change.

Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 include/linux/bpf_verifier.h |  6 +++++-
 kernel/bpf/verifier.c        | 11 ++++++-----
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 4c497e839526..42ce94ce96ba 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -637,6 +637,10 @@ enum priv_stack_mode {
 	PRIV_STACK_ADAPTIVE,
 };
 
+enum packet_access_flags {
+	PA_F_DIRECT_WRITE = BIT(0),
+};
+
 struct bpf_subprog_info {
 	/* 'start' has to be the first field otherwise find_subprog() won't work */
 	u32 start; /* insn idx of function entry point */
@@ -760,7 +764,7 @@ struct bpf_verifier_env {
 	bool bpf_capable;
 	bool bypass_spec_v1;
 	bool bypass_spec_v4;
-	bool seen_direct_write;
+	u8 seen_packet_access;	/* combination of enum packet_access_flags */
 	bool seen_exception;
 	struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
 	const struct bpf_line_info *prev_linfo;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 64a04b7dd500..4c84b0cd399e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7625,7 +7625,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 					value_regno);
 				return -EACCES;
 			}
-			env->seen_direct_write = true;
+			env->seen_packet_access |= PA_F_DIRECT_WRITE;
 		}
 		err = check_packet_access(env, regno, off, size, false);
 		if (!err && t == BPF_READ && value_regno >= 0)
@@ -13768,7 +13768,7 @@ static int check_special_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_ca
 				verbose(env, "the prog does not allow writes to packet data\n");
 				return -EINVAL;
 			}
-			env->seen_direct_write = true;
+			env->seen_packet_access |= PA_F_DIRECT_WRITE;
 		}
 
 		if (!meta->initialized_dynptr.id) {
@@ -21200,6 +21200,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 	struct bpf_prog *new_prog;
 	enum bpf_access_type type;
 	bool is_narrower_load;
+	bool seen_direct_write;
 	int epilogue_idx = 0;
 
 	if (ops->gen_epilogue) {
@@ -21227,13 +21228,13 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
 		}
 	}
 
-	if (ops->gen_prologue || env->seen_direct_write) {
+	seen_direct_write = env->seen_packet_access & PA_F_DIRECT_WRITE;
+	if (ops->gen_prologue || seen_direct_write) {
 		if (!ops->gen_prologue) {
 			verifier_bug(env, "gen_prologue is null");
 			return -EFAULT;
 		}
-		cnt = ops->gen_prologue(insn_buf, env->seen_direct_write,
-					env->prog);
+		cnt = ops->gen_prologue(insn_buf, seen_direct_write, env->prog);
 		if (cnt >= INSN_BUF_SIZE) {
 			verifier_bug(env, "prologue is too long");
 			return -EFAULT;

-- 
2.43.0