Feedback-ID: i6a694271:Fastmail
From:   Daniel Xu <dxu@dxuuu.xyz>
To:     corbet@lwn.net, daniel@iogearbox.net, andrii@kernel.org,
        martin.lau@linux.dev, ast@kernel.org
Cc:     song@kernel.org, yhs@fb.com, john.fastabend@gmail.com,
        kpsingh@kernel.org, sdf@google.com, haoluo@google.com,
        jolsa@kernel.org, bpf@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH bpf-next v2 2/8] bpf: verifier: Support KF_CHANGES_PKT flag
Date:   Mon, 27 Feb 2023 12:51:04 -0700
Message-Id: <991bc64ee4013bc81d7d4ab908d541d8978595a8.1677526810.git.dxu@dxuuu.xyz>
In-Reply-To: <cover.1677526810.git.dxu@dxuuu.xyz>
References: <cover.1677526810.git.dxu@dxuuu.xyz>
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KF_CHANGES_PKT indicates that the kfunc call may change packet data.
This is analogous to bpf_helper_changes_pkt_data().

Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
---
 Documentation/bpf/kfuncs.rst | 7 +++++++
 include/linux/btf.h          | 1 +
 kernel/bpf/verifier.c        | 8 ++++++++
 3 files changed, 16 insertions(+)

diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
index 226313747be5..16c387ee987f 100644
--- a/Documentation/bpf/kfuncs.rst
+++ b/Documentation/bpf/kfuncs.rst
@@ -260,6 +260,13 @@ encouraged to make their use-cases known as early as possible, and participate
 in upstream discussions regarding whether to keep, change, deprecate, or remove
 those kfuncs if and when such discussions occur.
 
+2.4.10 KF_CHANGES_PKT flag
+-----------------
+
+The KF_CHANGES_PKT is used for kfuncs that may change packet data.
+After calls to such kfuncs, existing packet pointers will be invalidated
+and must be revalidated before the prog can access packet data.
+
 2.5 Registering the kfuncs
 --------------------------
 
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 49e0fe6d8274..ee3d6c3e6cc0 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -71,6 +71,7 @@
 #define KF_SLEEPABLE    (1 << 5) /* kfunc may sleep */
 #define KF_DESTRUCTIVE  (1 << 6) /* kfunc performs destructive actions */
 #define KF_RCU          (1 << 7) /* kfunc only takes rcu pointer arguments */
+#define KF_CHANGES_PKT  (1 << 8) /* kfunc may change packet data */
 
 /*
  * Tag marking a kernel function as a kfunc. This is meant to minimize the
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5cb8b623f639..e58065498a35 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8681,6 +8681,11 @@ static bool is_kfunc_rcu(struct bpf_kfunc_call_arg_meta *meta)
 	return meta->kfunc_flags & KF_RCU;
 }
 
+static bool is_kfunc_changes_pkt(struct bpf_kfunc_call_arg_meta *meta)
+{
+	return meta->kfunc_flags & KF_CHANGES_PKT;
+}
+
 static bool is_kfunc_arg_kptr_get(struct bpf_kfunc_call_arg_meta *meta, int arg)
 {
 	return arg == 0 && (meta->kfunc_flags & KF_KPTR_GET);
@@ -10083,6 +10088,9 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			mark_btf_func_reg_size(env, regno, t->size);
 	}
 
+	if (is_kfunc_changes_pkt(&meta))
+		clear_all_pkt_pointers(env);
+
 	return 0;
 }
 
-- 
2.39.1