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| author | John Fastabend <john.fastabend@gmail.com> | 2020-09-24 21:45:06 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2020-09-26 02:47:21 +0300 |
| commit | 4fbb38a3b2cc7bf4340fe9bd9c73622760adc19d (patch) | |
| tree | 1e4be30e2794b80015074db7f3753054a11940f8 /kernel/bpf | |
| parent | 84085f877295b6b12d95262ec4082447214b09be (diff) | |
| download | linux-4fbb38a3b2cc7bf4340fe9bd9c73622760adc19d.tar.xz | |
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 <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf')
| -rw-r--r-- | kernel/bpf/verifier.c | 6 |
1 files 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; } |