linux-kernel - [PATCH bpf-next 2/6] bpf: verifier: Support KF_CHANGES

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Message-Id: <fc37530d6cf954c3ebd1173d2bdc6b731c733134.1671049840.git.dxu@dxuuu.xyz>
Date:   Wed, 14 Dec 2022 16:25:29 -0700
From:   Daniel Xu <dxu@...uu.xyz>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Jonathan Corbet <corbet@....net>
Cc:     ppenkov@...atrix.com, dbird@...atrix.com, bpf@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next 2/6] bpf: verifier: Support KF_CHANGES_PKT flag

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@...uu.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 9fd7fb539f85..061ab392a02f 100644
--- a/Documentation/bpf/kfuncs.rst
+++ b/Documentation/bpf/kfuncs.rst
@@ -200,6 +200,13 @@ single argument which must be a trusted argument or a MEM_RCU pointer.
 The argument may have reference count of 0 and the kfunc must take this
 into consideration.
 
+2.4.9 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 5f628f323442..0575f530e40b 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 */
 
 /*
  * Return the name of the passed struct, if exists, or halt the build if for
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a5255a0dcbb6..0ac505cbd6ba 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8213,6 +8213,11 @@ 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);
@@ -9313,6 +9318,9 @@ 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;
 }
 
-- 
2.39.0