On Tue, 2023-11-21 at 17:16 -0800, Andrii Nakryiko wrote:
> BPF verifier expects callback subprogs to return values from specified
> range (typically [0, 1]). This requires that r0 at exit is both precise
> (because we rely on specific value range) and is marked as read
> (otherwise state comparison will ignore such register as unimportant).
>
> Add a simple test that validates that all these conditions are enforced.
>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---
Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
[...]
> +SEC("?raw_tp")
> +__failure __log_level(2)
> +__flag(BPF_F_TEST_STATE_FREQ)
Nit: although it is redundant, but maybe also check precision log to
check that r0 is indeed marked precise?
> +__msg("from 10 to 12: frame1: R0=scalar(umin=1001) R10=fp0 cb")
> +__msg("At callback return the register R0 has unknown scalar value should have been in (0x0; 0x1)")
> +__naked int callback_precise_return_fail(void)
[...]
