netdev - [PATCH net-next 4/7] bpf: improve verifier liveness marks

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Date:   Thu, 30 Nov 2017 21:31:38 -0800
From:   Alexei Starovoitov <ast@...com>
To:     "David S . Miller" <davem@...emloft.net>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        <netdev@...r.kernel.org>, <kernel-team@...com>
Subject: [PATCH net-next 4/7] bpf: improve verifier liveness marks

registers with pointers filled from stack were missing live_written marks
which caused liveness propagation to unnecessary mark more registers as
live_read and miss state pruning opportunities later on.

                     before  after
bpf_lb-DLB_L3.o       2285   2270
bpf_lb-DLB_L4.o       3723   3682
bpf_lb-DUNKNOWN.o     1110   1110
bpf_lxc-DDROP_ALL.o   27954  27876
bpf_lxc-DUNKNOWN.o    38954  38780
bpf_netdev.o          16943  16937
bpf_overlay.o         7929   7929

Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Acked-by: John Fastabend <john.fastabend@...il.com>
Acked-by: Daniel Borkmann <daniel@...earbox.net>
---
 kernel/bpf/verifier.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 14ad7c6e806a..46ff4e5b3fb7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -795,6 +795,11 @@ static int check_stack_read(struct bpf_verifier_env *env,
 		if (value_regno >= 0) {
 			/* restore register state from stack */
 			state->regs[value_regno] = state->stack[spi].spilled_ptr;
+			/* mark reg as written since spilled pointer state likely
+			 * has its liveness marks cleared by is_state_visited()
+			 * which resets stack/reg liveness for state transitions
+			 */
+			state->regs[value_regno].live |= REG_LIVE_WRITTEN;
 			mark_stack_slot_read(state, spi);
 		}
 		return 0;
-- 
2.9.5