[PATCH bpf-next 2/3] bpf: verifier: teach the verifier to reason about the BPF_JSET instruction

[Jakub Kicinski]

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.kicin...@netronome.com>
Reviewed-by: Jiong Wang <jiong.w...@netronome.com>
---
 kernel/bpf/verifier.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8b511a4fe84a..50bb45aa4f26 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3788,6 +3788,12 @@ 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;
@@ -3872,6 +3878,13 @@ 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);
@@ -3944,6 +3957,13 @@ 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);
-- 
2.17.1