Re: [PATCH v2 bpf-next] bpf: Fix latent unsoundness in and/or/xor value tracking

[Daniel Borkmann <daniel@iogearbox.net>]

On 4/2/24 11:20 PM, Harishankar Vishwanathan wrote:
[...]
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index fcb62300f407..a7404a7d690f 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -13326,23 +13326,21 @@ static void scalar32_min_max_and(struct bpf_reg_state *dst_reg,
>   		return;
>   	}
>   
> -	/* We get our minimum from the var_off, since that's inherently
> +	/* We get our minimum from the var32_off, since that's inherently
>   	 * bitwise.  Our maximum is the minimum of the operands' maxima.
>   	 */
>   	dst_reg->u32_min_value = var32_off.value;
>   	dst_reg->u32_max_value = min(dst_reg->u32_max_value, umax_val);
> -	if (dst_reg->s32_min_value < 0 || smin_val < 0) {

The smin_val is now unused, triggering the following warnings :

../kernel/bpf/verifier.c:13321:6: warning: unused variable 'smin_val' [-Wunused-variable]
  13321 |         s32 smin_val = src_reg->s32_min_value;
        |             ^~~~~~~~
../kernel/bpf/verifier.c:13352:6: warning: unused variable 'smin_val' [-Wunused-variable]
  13352 |         s64 smin_val = src_reg->smin_value;
        |             ^~~~~~~~
../kernel/bpf/verifier.c:13386:6: warning: unused variable 'smin_val' [-Wunused-variable]
  13386 |         s32 smin_val = src_reg->s32_min_value;
        |             ^~~~~~~~
../kernel/bpf/verifier.c:13417:6: warning: unused variable 'smin_val' [-Wunused-variable]
  13417 |         s64 smin_val = src_reg->smin_value;
        |             ^~~~~~~~
../kernel/bpf/verifier.c:13451:6: warning: unused variable 'smin_val' [-Wunused-variable]
  13451 |         s32 smin_val = src_reg->s32_min_value;
        |             ^~~~~~~~
../kernel/bpf/verifier.c:13479:6: warning: unused variable 'smin_val' [-Wunused-variable]
  13479 |         s64 smin_val = src_reg->smin_value;
        |             ^~~~~~~~

Removing these builds fine then, please follow-up with a v3.

Thanks,
Daniel