linux-kernel - RE: [RFC PATCH net-next 2/6] x86: bpf_jit_comp: support BPF_S_ANC_SECCOMP_LD

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Message-ID: <1366990066.8964.216.camel@edumazet-glaptop>
Date:	Fri, 26 Apr 2013 08:27:46 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Xi Wang <xi.wang@...il.com>, Daniel Borkmann <dborkman@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Russell King <linux@....linux.org.uk>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Will Drewry <wad@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: RE: [RFC PATCH net-next 2/6] x86: bpf_jit_comp: support
 BPF_S_ANC_SECCOMP_LD_W instruction

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]);




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