Messages in this thread |  | | From | Andy Lutomirski <> | Date | Thu, 31 Oct 2013 16:50:44 -0700 | Subject | Re: ARM seccomp filters and EABI/OABI |
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On Tue, Oct 29, 2013 at 12:38 PM, Paul Moore <paul@paul-moore.com> wrote: > On Monday, October 28, 2013 11:16:20 PM Richard Weinberger wrote: >> Am 28.10.2013 22:53, schrieb Paul Moore: >> > On Thursday, October 24, 2013 09:55:57 PM Richard Weinberger wrote: >> >> On Wed, Oct 23, 2013 at 11:02 PM, Andy Lutomirski <luto@amacapital.net> >> > >> > wrote: >> >>> I'm looking at the seccomp code, the ARM entry code, and the >> >>> syscall(2) manpage, and I'm a bit lost. (The fact that I don't really >> >>> speak ARM assembly doesn't help.) My basic question is: what happens >> >>> if an OABI syscall happens? >> >>> >> >>> AFAICS, the syscall arguments for EABI are r0..r5, although their >> >>> ordering is a bit odd*. For OABI, r6 seems to play some role, but I'm >> >>> lost as to what it is. The seccomp_bpf_load function won't load r6, >> >>> so there had better not be anything useful in there... (Also, struct >> >>> seccomp_data will have issues with a seventh "argument".) >> >>> >> >>> But what happens to the syscall number? For an EABI syscall, it's in >> >>> r7. For an OABI syscall, it's in the swi instruction and gets copied >> >>> to r7 on entry. If a debugger changes r7, presumably the syscall >> >>> number changes. >> >>> >> >>> Oddly, there are two different syscall tables. The major differences >> >>> seem to be that some of the OABI entries have their argument order >> >>> changed. But there's also a magic constant 0x900000 added to the >> >>> syscall number somewhere -- is it reflected in _sigsys._syscall? Is >> >>> it reflected in ucontext's r7? >> >>> >> >>> I'm a bit surprised to see that both the EABI and OABI ABIs show up as >> >>> AUDIT_ARCH_ARM. >> >>> >> >>> Can any of you shed some light on this? I don't have an ARM system I >> >>> can test on, but if one of you can point me at a decent QEMU image, I >> >>> can play around. >> >> >> >> Maybe this helps: >> >> http://people.debian.org/~aurel32/qemu/armel/ >> > >> > Thanks for the pointer, although those images look quite old, has anyone >> > done a refresh? >> >> You are free to run "apt-get upgrade" within the said images. :-) > > Okay, true ;)
Except it didn't work... I fixed it with 'apt-key adv --recv-keys --keyserver keyserver.ubuntu.com <key id from update's error message>'.
I have yet to build a working kernel for this thing, though. Apparently kernels since 3.8 have something wrong in the "versatile" board file. Do any of you have a working .config and qemu -M option?
> > -- > paul moore > www.paul-moore.com >
-- Andy Lutomirski AMA Capital Management, LLC
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