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

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Date:	Fri, 26 Apr 2013 16:15:02 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Xi Wang" <xi.wang@...il.com>,
	"Eric Dumazet" <eric.dumazet@...il.com>
Cc:	"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

> >> +#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...

	David



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