RE: [RFC PATCH net-next 2/6] x86: bpf_jit_comp: support BPF_S_ANC_SECCOMP_LD_W instruction

David Laight
2013-04-26T15:15:02Z

> >> +#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