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bpf: verifier: teach the verifier to reason about the BPF_JSET instruction 

Some JITs (nfp) try to optimize code on their own.  It could make
sense in case of BPF_JSET instruction which is currently not interpreted
by the verifier, meaning for instance that dead could would not be
detected if it was under BPF_JSET branch.

Teach the verifier basics of BPF_JSET, JIT optimizations will be
removed shortly.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Jiong Wang <jiong.wang@netronome.com>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Jakub Kicinski 2018-12-19 22:13:04 -08:00 committed by Daniel Borkmann
parent 5a8d5209ac
commit 960ea05656
1 changed files with 20 additions and 0 deletions
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20
kernel/bpf/verifier.c
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@ -3859,6 +3859,12 @@ static int is_branch_taken(struct bpf_reg_state *reg, u64 val, u8 opcode)
if (tnum_is_const(reg->var_off))
return !tnum_equals_const(reg->var_off, val);
break;
case BPF_JSET:
if ((~reg->var_off.mask & reg->var_off.value) & val)
return 1;
if (!((reg->var_off.mask | reg->var_off.value) & val))
return 0;
break;
case BPF_JGT:
if (reg->umin_value > val)
return 1;
@ -3943,6 +3949,13 @@ static void reg_set_min_max(struct bpf_reg_state *true_reg,
*/
__mark_reg_known(false_reg, val);
break;
case BPF_JSET:
false_reg->var_off = tnum_and(false_reg->var_off,
tnum_const(~val));
if (is_power_of_2(val))
true_reg->var_off = tnum_or(true_reg->var_off,
tnum_const(val));
break;
case BPF_JGT:
false_reg->umax_value = min(false_reg->umax_value, val);
true_reg->umin_value = max(true_reg->umin_value, val + 1);
@ -4015,6 +4028,13 @@ static void reg_set_min_max_inv(struct bpf_reg_state *true_reg,
*/
__mark_reg_known(false_reg, val);
break;
case BPF_JSET:
false_reg->var_off = tnum_and(false_reg->var_off,
tnum_const(~val));
if (is_power_of_2(val))
true_reg->var_off = tnum_or(true_reg->var_off,
tnum_const(val));
break;
case BPF_JGT:
true_reg->umax_value = min(true_reg->umax_value, val - 1);
false_reg->umin_value = max(false_reg->umin_value, val);