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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>
hifive-unleashed-5.1
Alexei Starovoitov 2017-11-30 21:31:38 -08:00 committed by Daniel Borkmann
parent 19ceb4178d
commit 2f18f62ee1
1 changed files with 5 additions and 0 deletions
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5
kernel/bpf/verifier.c
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@ -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;