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@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 14ad7c6e806ab3650edd1860f587d9c2af1af8ab..46ff4e5b3fb7d5291afb33e6d8b676a99a55c796 100644 (file)
--- 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;