From 4fbb38a3b2cc7bf4340fe9bd9c73622760adc19d Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Thu, 24 Sep 2020 11:45:06 -0700 Subject: bpf, verifier: Remove redundant var_off.value ops in scalar known reg cases In BPF_AND and BPF_OR alu cases we have this pattern when the src and dst tnum is a constant. 1 dst_reg->var_off = tnum_[op](dst_reg->var_off, src_reg.var_off) 2 scalar32_min_max_[op] 3 if (known) return 4 scalar_min_max_[op] 5 if (known) 6 __mark_reg_known(dst_reg, dst_reg->var_off.value [op] src_reg.var_off.value) The result is in 1 we calculate the var_off value and store it in the dst_reg. Then in 6 we duplicate this logic doing the op again on the value. The duplication comes from the the tnum_[op] handlers because they have already done the value calcuation. For example this is tnum_and(). struct tnum tnum_and(struct tnum a, struct tnum b) { u64 alpha, beta, v; alpha = a.value | a.mask; beta = b.value | b.mask; v = a.value & b.value; return TNUM(v, alpha & beta & ~v); } So lets remove the redundant op calculation. Its confusing for readers and unnecessary. Its also not harmful because those ops have the property, r1 & r1 = r1 and r1 | r1 = r1. Signed-off-by: John Fastabend Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d4ba29fb17a6..b25ba989c2dc 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5849,8 +5849,7 @@ static void scalar_min_max_and(struct bpf_reg_state *dst_reg, u64 umax_val = src_reg->umax_value; if (src_known && dst_known) { - __mark_reg_known(dst_reg, dst_reg->var_off.value & - src_reg->var_off.value); + __mark_reg_known(dst_reg, dst_reg->var_off.value); return; } @@ -5920,8 +5919,7 @@ static void scalar_min_max_or(struct bpf_reg_state *dst_reg, u64 umin_val = src_reg->umin_value; if (src_known && dst_known) { - __mark_reg_known(dst_reg, dst_reg->var_off.value | - src_reg->var_off.value); + __mark_reg_known(dst_reg, dst_reg->var_off.value); return; } -- cgit v1.2.3