bpf/verifier: fix bounds calculation on BPF_RSH

[linux-2.6-microblaze.git] / kernel / bpf / verifier.c

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e39b013..625e358 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2190,20 +2190,22 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env,
                        mark_reg_unknown(env, regs, insn->dst_reg);
                        break;
                }
-               /* BPF_RSH is an unsigned shift, so make the appropriate casts */
-               if (dst_reg->smin_value < 0) {
-                       if (umin_val) {
-                               /* Sign bit will be cleared */
-                               dst_reg->smin_value = 0;
-                       } else {
-                               /* Lost sign bit information */
-                               dst_reg->smin_value = S64_MIN;
-                               dst_reg->smax_value = S64_MAX;
-                       }
-               } else {
-                       dst_reg->smin_value =
-                               (u64)(dst_reg->smin_value) >> umax_val;
-               }
+               /* BPF_RSH is an unsigned shift.  If the value in dst_reg might
+                * be negative, then either:
+                * 1) src_reg might be zero, so the sign bit of the result is
+                *    unknown, so we lose our signed bounds
+                * 2) it's known negative, thus the unsigned bounds capture the
+                *    signed bounds
+                * 3) the signed bounds cross zero, so they tell us nothing
+                *    about the result
+                * If the value in dst_reg is known nonnegative, then again the
+                * unsigned bounts capture the signed bounds.
+                * Thus, in all cases it suffices to blow away our signed bounds
+                * and rely on inferring new ones from the unsigned bounds and
+                * var_off of the result.
+                */
+               dst_reg->smin_value = S64_MIN;
+               dst_reg->smax_value = S64_MAX;
                if (src_known)
                        dst_reg->var_off = tnum_rshift(dst_reg->var_off,
                                                       umin_val);