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

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Message-ID: <57060ECE.9020300@iogearbox.net>
Date:	Thu, 07 Apr 2016 09:39:58 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Alexei Starovoitov <ast@...com>
CC:	"David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] bpf: simplify verifier register state assignments

On 04/07/2016 04:39 AM, Alexei Starovoitov wrote:
> 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>

Acked-by: Daniel Borkmann <daniel@...earbox.net>