Messages in this thread | ![/](/images/icornerl.gif) | | Subject | Re: [RFC PATCH net-next 2/6] x86: bpf_jit_comp: support BPF_S_ANC_SECCOMP_LD_W instruction | From | Eric Dumazet <> | Date | Fri, 26 Apr 2013 08:11:34 -0700 |
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On Fri, 2013-04-26 at 10:50 -0400, Xi Wang wrote: > On Fri, Apr 26, 2013 at 10:18 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > > On Fri, 2013-04-26 at 03:51 -0400, Xi Wang 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? > > > This cannot have been tested at all. > > Thanks to QEMU for hiding bugs then. :)
1) 'current' at the time the code is jitted (compiled) is not the 'current' at the time the filter will be evaluated.
On x86_64, if CONFIG_IA32_EMULATION=y, syscall_get_arch() evaluates to :
if (task_thread_info(task)->status & TS_COMPAT) return AUDIT_ARCH_I386; return AUDIT_ARCH_X86_64;
So your code is completely wrong.
2) Calling a function potentially destroys some registers. %rdi,%r8,%r9 for instance, so we are going to crash very easily.
I dont know, I feel a bit uncomfortable having to explain this to someone sending security related patches...
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