netdev - [PATCH 2/5] Replace invocation of weak PRNG in kernel/bpf/core.c

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Date:   Mon, 12 Dec 2022 00:16:05 +0200
From:   david.keisarschm@...l.huji.ac.il
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     David <david.keisarschm@...l.huji.ac.il>, aksecurity@...il.com,
        ilay.bahat1@...il.com, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH 2/5] Replace invocation of weak PRNG in kernel/bpf/core.c

From: David <david.keisarschm@...l.huji.ac.il>

We changed the invocation of
 prandom_u32_state to get_random_u32.
 We deleted the maintained state,
 which was a CPU-variable,
 since get_random_u32 maintains its own CPU-variable.
 We also deleted the state initializer,
 since it is not needed anymore.

Signed-off-by: David <david.keisarschm@...l.huji.ac.il>
---
 include/linux/bpf.h   |  1 -
 kernel/bpf/core.c     | 13 +------------
 kernel/bpf/verifier.c |  2 --
 net/core/filter.c     |  1 -
 4 files changed, 1 insertion(+), 16 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index c1bd1bd10..0689520b9 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2572,7 +2572,6 @@ const struct bpf_func_proto *tracing_prog_func_proto(
   enum bpf_func_id func_id, const struct bpf_prog *prog);
 
 /* Shared helpers among cBPF and eBPF. */
-void bpf_user_rnd_init_once(void);
 u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
 u64 bpf_get_raw_cpu_id(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
 
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 4cb5421d9..a6f06894e 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2579,13 +2579,6 @@ void bpf_prog_free(struct bpf_prog *fp)
 }
 EXPORT_SYMBOL_GPL(bpf_prog_free);
 
-/* RNG for unpriviledged user space with separated state from prandom_u32(). */
-static DEFINE_PER_CPU(struct rnd_state, bpf_user_rnd_state);
-
-void bpf_user_rnd_init_once(void)
-{
-	prandom_init_once(&bpf_user_rnd_state);
-}
 
 BPF_CALL_0(bpf_user_rnd_u32)
 {
@@ -2595,12 +2588,8 @@ BPF_CALL_0(bpf_user_rnd_u32)
 	 * transformations. Register assignments from both sides are
 	 * different, f.e. classic always sets fn(ctx, A, X) here.
 	 */
-	struct rnd_state *state;
 	u32 res;
-
-	state = &get_cpu_var(bpf_user_rnd_state);
-	res = predictable_rng_prandom_u32_state(state);
-	put_cpu_var(bpf_user_rnd_state);
+	res = get_random_u32();
 
 	return res;
 }
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 264b3dc71..9f22fb3fa 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14049,8 +14049,6 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 
 		if (insn->imm == BPF_FUNC_get_route_realm)
 			prog->dst_needed = 1;
-		if (insn->imm == BPF_FUNC_get_prandom_u32)
-			bpf_user_rnd_init_once();
 		if (insn->imm == BPF_FUNC_override_return)
 			prog->kprobe_override = 1;
 		if (insn->imm == BPF_FUNC_tail_call) {
diff --git a/net/core/filter.c b/net/core/filter.c
index bb0136e7a..7a595ac00 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -443,7 +443,6 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 			break;
 		case SKF_AD_OFF + SKF_AD_RANDOM:
 			*insn = BPF_EMIT_CALL(bpf_user_rnd_u32);
-			bpf_user_rnd_init_once();
 			break;
 		}
 		break;
-- 
2.38.0