@@ -14343,7 +14343,43 @@ static void regs_refine_cond_op(struct bpf_reg_state *reg1, struct bpf_reg_state
}
break;
case BPF_JNE:
- /* we don't derive any new information for inequality yet */
+ if (!is_reg_const(reg2, is_jmp32))
+ swap(reg1, reg2);
+ if (!is_reg_const(reg2, is_jmp32))
+ break;
+
+ /* try to recompute the bound of reg1 if reg2 is a const and
+ * is exactly the edge of reg1.
+ */
+ val = reg_const_value(reg2, is_jmp32);
+ if (is_jmp32) {
+ /* u32_min_value is not equal to 0xffffffff at this point,
+ * because otherwise u32_max_value is 0xffffffff as well,
+ * in such a case both reg1 and reg2 would be constants,
+ * jump would be predicted and reg_set_min_max() won't
+ * be called.
+ *
+ * Same reasoning works for all {u,s}{min,max}{32,64} cases
+ * below.
+ */
+ if (reg1->u32_min_value == (u32)val)
+ reg1->u32_min_value++;
+ if (reg1->u32_max_value == (u32)val)
+ reg1->u32_max_value--;
+ if (reg1->s32_min_value == (s32)val)
+ reg1->s32_min_value++;
+ if (reg1->s32_max_value == (s32)val)
+ reg1->s32_max_value--;
+ } else {
+ if (reg1->umin_value == (u64)val)
+ reg1->umin_value++;
+ if (reg1->umax_value == (u64)val)
+ reg1->umax_value--;
+ if (reg1->smin_value == (s64)val)
+ reg1->smin_value++;
+ if (reg1->smax_value == (s64)val)
+ reg1->smax_value--;
+ }
break;
case BPF_JSET:
if (!is_reg_const(reg2, is_jmp32))
We can derive some new information for BPF_JNE in regs_refine_cond_op(). Take following code for example: /* The type of "a" is u32 */ if (a > 0 && a < 100) { /* the range of the register for a is [0, 99], not [1, 99], * and will cause the following error: * * invalid zero-sized read * * as a can be 0. */ bpf_skb_store_bytes(skb, xx, xx, a, 0); } In the code above, "a > 0" will be compiled to "jmp xxx if a == 0". In the TRUE branch, the dst_reg will be marked as known to 0. However, in the fallthrough(FALSE) branch, the dst_reg will not be handled, which makes the [min, max] for a is [0, 99], not [1, 99]. For BPF_JNE, we can reduce the range of the dst reg if the src reg is a const and is exactly the edge of the dst reg. Signed-off-by: Menglong Dong <menglong8.dong@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com> --- v2: - fix a typo in the subject - add some comments, as Eduard advised --- kernel/bpf/verifier.c | 38 +++++++++++++++++++++++++++++++++++++- 1 file changed, 37 insertions(+), 1 deletion(-)