netdev - Re: [PATCH] s390/bpf: perform r1 range checking before accessing jit->seen

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Date:   Thu, 15 Jul 2021 19:02:01 +0200
From:   Ilya Leoshkevich <iii@...ux.ibm.com>
To:     Colin King <colin.king@...onical.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-s390@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] s390/bpf: perform r1 range checking before accessing
 jit->seen_reg[r1]

On Thu, 2021-07-15 at 13:57 +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently array jit->seen_reg[r1] is being accessed before the range
> checking of index r1. The range changing on r1 should be performed
> first since it will avoid any potential out-of-range accesses on the
> array seen_reg[] and also it is more optimal to perform checks on
> r1 before fetching data from the array.  Fix this by swapping the
> order of the checks before the array access.
> 
> Fixes: 054623105728 ("s390/bpf: Add s390x eBPF JIT compiler backend")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  arch/s390/net/bpf_jit_comp.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/s390/net/bpf_jit_comp.c
> b/arch/s390/net/bpf_jit_comp.c
> index 63cae0476bb4..2ae419f5115a 100644
> --- a/arch/s390/net/bpf_jit_comp.c
> +++ b/arch/s390/net/bpf_jit_comp.c
> @@ -112,7 +112,7 @@ static inline void reg_set_seen(struct bpf_jit
> *jit, u32 b1)
>  {
>         u32 r1 = reg2hex[b1];
>  
> -       if (!jit->seen_reg[r1] && r1 >= 6 && r1 <= 15)
> +       if (r1 >= 6 && r1 <= 15 && !jit->seen_reg[r1])
>                 jit->seen_reg[r1] = 1;
>  }
>  

Looks good to me, thanks!

Acked-by: Ilya Leoshkevich <iii@...ux.ibm.com>
Tested-by: Ilya Leoshkevich <iii@...ux.ibm.com>