bpf: speed up stacksafe check

Alexei Starovoitov · borkmann · commit b233920c97a6 · 2018-12-15T01:28:32.000+01:00
Don't check the same stack liveness condition 8 times.
once is enough.

Signed-off-by: Alexei Starovoitov &lt;ast@kernel.org&gt;
Acked-by: Edward Cree &lt;ecree@solarflare.com&gt;
Acked-by: Jakub Kicinski &lt;jakub.kicinski@netronome.com&gt;
Signed-off-by: Daniel Borkmann &lt;daniel@iogearbox.net&gt;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
@@ -5204,9 +5204,11 @@ static bool stacksafe(struct bpf_func_state *old,
 	for (i = 0; i < old->allocated_stack; i++) {
 		spi = i / BPF_REG_SIZE;
 
-		if (!(old->stack[spi].spilled_ptr.live & REG_LIVE_READ))
+		if (!(old->stack[spi].spilled_ptr.live & REG_LIVE_READ)) {
+			i += BPF_REG_SIZE - 1;
 			/* explored state didn't use this */
 			continue;
+		}
 
 		if (old->stack[spi].slot_type[i % BPF_REG_SIZE] == STACK_INVALID)
 			continue;
