linux-kernel - Re: [PATCH 2/2] ARM: net: bpf_jit_32: fix sp-relative load/stores offsets.

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Date:	Sat, 08 Dec 2012 00:15:56 +0100
From:	Mircea Gherzan <mgherzan@...il.com>
To:	Nicolas Schichan <nschichan@...ebox.fr>
CC:	rmk+kernel@....linux.org.uk, Russell King <linux@....linux.org.uk>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ARM: net: bpf_jit_32: fix sp-relative load/stores
 offsets.

Am 06.12.2012 15:38, schrieb Nicolas Schichan:
> The offset must be multiplied by 4 to be sure to access the correct
> 32bit word in the stack scratch space.
> 
> For instance, a store at scratch memory cell #1 was generating the
> following:
> 
> st	r4, [sp, #1]
> 
> While the correct code for this is:
> 
> st	r4, [sp, #4]
> 
> To reproduce the bug (assuming your system has a NIC with the mac
> address 52:54:00:12:34:56):
> 
> echo 0 > /proc/sys/net/core/bpf_jit_enable
> tcpdump -ni eth0 "ether[1] + ether[2] - ether[3] * ether[4] - ether[5] \
> 	== -0x3AA" # this will capture packets as expected
> 
> echo 1 > /proc/sys/net/core/bpf_jit_enable
> tcpdump -ni eth0 "ether[1] + ether[2] - ether[3] * ether[4] - ether[5] \
> 	== -0x3AA" # this will not.
> 
> This bug was present since the original inclusion of bpf_jit for ARM
> (ddecdfce: ARM: 7259/3: net: JIT compiler for packet filters).
> 
> Signed-off-by: Nicolas Schichan <nschichan@...ebox.fr>
> ---
>  arch/arm/net/bpf_jit_32.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
> index a64d349..b6f305e 100644
> --- a/arch/arm/net/bpf_jit_32.c
> +++ b/arch/arm/net/bpf_jit_32.c
> @@ -42,7 +42,7 @@
>  #define r_skb_hl	ARM_R8
>  
>  #define SCRATCH_SP_OFFSET	0
> -#define SCRATCH_OFF(k)		(SCRATCH_SP_OFFSET + (k))
> +#define SCRATCH_OFF(k)		(SCRATCH_SP_OFFSET + 4 * (k))
>  
>  #define SEEN_MEM		((1 << BPF_MEMWORDS) - 1)
>  #define SEEN_MEM_WORD(k)	(1 << (k))

Acked-by: Mircea Gherzan <mgherzan@...il.com>
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