From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: RE: [RFC PATCH net-next 2/6] x86: bpf_jit_comp: support
 BPF_S_ANC_SECCOMP_LD_W instruction
Date: Fri, 26 Apr 2013 08:27:46 -0700
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Cc: Xi Wang <xi.wang@gmail.com>, Daniel Borkmann <dborkman@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Russell King <linux@arm.linux.org.uk>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Eric Dumazet <edumazet@google.com>,
	Will Drewry <wad@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
To: David Laight <David.Laight@ACULAB.COM>
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On Fri, 2013-04-26 at 16:15 +0100, David Laight wrote:
> > >> +#ifdef CONFIG_SECCOMP_FILTER
> > >> +                     case BPF_S_ANC_SECCOMP_LD_W:
> > >> +                             if (K == offsetof(struct seccomp_data, arch)) {
> > >> +                                     int arch = syscall_get_arch(current, NULL);
> > >> +
> > >> +                                     EMIT1_off32(0xb8, arch); /* mov arch,%eax */
> > >> +                                     break;
> > >> +                             }
> > >> +                             func = (u8 *)seccomp_bpf_load;
> > >> +                             t_offset = func - (image + addrs[i]);
> > >> +                             EMIT1_off32(0xbf, K); /* mov imm32,%edi */
> > >> +                             EMIT1_off32(0xe8, t_offset); /* call seccomp_bpf_load */
> > >> +                             break;
> > >> +#endif
> > >
> > > This seems seriously wrong to me.
> > 
> > Can you elaborate?
> 
> The 'call seccomp_bpf_load' needs a pc-relative offset,
> I assume that is what EMIT1_off32() generates.
> 
> The other two instructions want an absolute 32 bit value...

Hmm, this part is fine, we perform the relative adjustments in 
t_offset = func - (image + addrs[i]);