netdev - Re: [PATCH net-next] bpf: simplify verifier register state assignments

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Date:	Sun, 10 Apr 2016 22:43:56 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	ast@...com
Cc:	daniel@...earbox.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] bpf: simplify verifier register state
 assignments

From: Alexei Starovoitov <ast@...com>
Date: Wed, 6 Apr 2016 19:39:21 -0700

> verifier is using the following structure to track the state of registers:
> struct reg_state {
>     enum bpf_reg_type type;
>     union {
>         int imm;
>         struct bpf_map *map_ptr;
>     };
> };
> and later on in states_equal() does memcmp(&old->regs[i], &cur->regs[i],..)
> to find equivalent states.
> Throughout the code of verifier there are assignements to 'imm' and 'map_ptr'
> fields and it's not obvious that most of the assignments into 'imm' don't
> need to clear extra 4 bytes (like mark_reg_unknown_value() does) to make sure
> that memcmp doesn't go over junk left from 'map_ptr' assignment.
> 
> Simplify the code by converting 'int' into 'long'
> 
> Suggested-by: Daniel Borkmann <daniel@...earbox.net>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>

Applied, thanks Daniel.